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Zendra, O.: Visualization of the static aspects of software: a survey. IEEE Trans. Vis. Comput. Graph. 17(7), 913-933

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Abstract and Figures

Software is usually complex and always intangible. In practice, the development and maintenance processes are time-consuming activities mainly because software complexity is difficult to manage. Graphical visualization of software has the potential to result in a better and faster understanding of its design and functionality, thus saving time and providing valuable information to improve its quality. However, visualizing software is not an easy task because of the huge amount of information comprised in the software. Furthermore, the information content increases significantly once the time dimension to visualize the evolution of the software is taken into account. Human perception of information and cognitive factors must thus be taken into account to improve the understandability of the visualization. In this paper, we survey visualization techniques, both 2D- and 3D-based, representing the static aspects of the software and its evolution. We categorize these techniques according to the issues they focus on, in order to help compare them and identify the most relevant techniques and tools for a given problem.
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Visualization of the Static Aspects
of Software: A Survey
Pierre Caserta and Olivier Zendra
Abstract—Software is usually complex and always intangible. In practice, the development and maintenance processes are time-
consuming activities mainly because software complexity is difficult to manage. Graphical visualization of software has the potential to
result in a better and faster understanding of its design and functionality, thus saving time and providing valuable information to
improve its quality. However, visualizing software is not an easy task because of the huge amount of information comprised in the
software. Furthermore, the information content increases significantly once the time dimension to visualize the evolution of the
software is taken into account. Human perception of information and cognitive factors must thus be taken into account to improve the
understandability of the visualization. In this paper, we survey visualization techniques, both 2D- and 3D-based, representing the static
aspects of the software and its evolution. We categorize these techniques according to the issues they focus on, in order to help
compare them and identify the most relevant techniques and tools for a given problem.
Index Terms—Visualization of software, software comprehension, software maintenance, human perception.
Ç
1INTRODUCTION
SOFTWARE quickly becomes very complex when its size
increases, which hinders its development. The very large
amount of information represented in software, at all
granularity levels, especially the tremendous number of
interactions between software elements, make understand-
ing software a very difficult, lengthy, and error-prone task.
This is even truer when one has not been involved in its
original development.
The maintenance process is indeed known to be the most
time-consuming and expensive phase of the software life
cycle [54]. Most of the time spent in this maintenance
process is devoted to understanding the maintained system.
Hence, tools designed to help understand software can
significantly reduce development time and cost [55], [56].
Moreover, software is virtual and intangible [14]. With-
out a visualization technique, it is thus very hard to make a
clear mental representation of what a piece of software is.
Basically, visualizing a piece of software amounts to
drawing a picture of the software [57], because humans
are better at deducing information from graphical images
than numerical information [58], [59], [60]. One way to ease
the understanding of the source code is to represent it
through suitable abstractions and metaphors. This way,
software visualization provides a more tangible view of the
software [61], [62]. Experiments have shown that using
visualization techniques in a software development project
increases the odds of succeeding [63], [64].
Visual representation of software relies on the human
perceptual system [65]. Using the latter effectively is
important to reduce the user cognitive load [66], [67], [68].
Indeed, how people perceive and interact with a visualiza-
tion tool strongly influences their understanding of the
data, hence the usefulness of the system [65], [69], [70]. In
this paper, we survey 2D and 3D visualizations as a whole,
since both have pros and cons [71], [72]. 2D visualizations
have actually been the subject of many studies and began to
appear in commercial products [73], [74], but the recent
trend is to explore 3D software visualizations [75], [76]
despite the intrinsic 3D navigation problem [77].
Software visualization can address three distinct kinds of
aspects of software (static, dynamic, and evolution) [62]. The
visualization of the static aspects of software focuses on
visualizing software as it is coded, and dealing with
information that is valid for all possible executions of the
software. Conversely, the visualization of the dynamic aspects
of software provides information about a particular run of the
software and helps understand program behavior. Finally,
the visualization of the evolution of the static aspects of software
adds the time dimension to the visualization of the static
aspect of software. We tackle only the visualization of the
static aspects of software and its evolution in this paper;
dynamic aspects of software fall beyond its scope.
Over the past few years, researchers have proposed many
software visualization techniques and various taxonomies
have been published [78], [79], [80], [81]. Some prior works
[82], [83], [84], [85] dealt with the state of the art of similar
fields at the time they were written, but they do not include
the most recent developments. Other more recent works [76],
[86] cover only a particular subset of the domain. Conversely,
our paper is an up-to-date survey on the whole domain of
visualization of the static aspects of software and its
evolution. We present a very wide coverage of different
kinds of visualization techniques, explaining each one and
giving its pros and cons.
IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011 913
.P. Caserta is with the LORIA Laboratory, INPL Nancy University, Office
C-123, 615 Rue du Jardin Botanique, CS 20101, 54603, Villers-les-Nancy
Cedex, France. E-mail: Pierre.Caserta@loria.fr.
.O. Zendra is with the INRIA Nancy Grand-Est, Office C-124, 615 Rue du
Jardin Botanique, CS 20101, 54603, Villers-les-Nancy Cedex, France.
E-mail: Olivier.Zendra@inria.fr.
Manuscript received 7 Oct. 2009; revised 19 Mar. 2010; accepted 29 July
2010; published online 20 Aug. 2010.
Recommended for acceptance by A. MacEachren.
For information on obtaining reprints of this article, please send e-mail to:
tvcg@computer.org, and reference IEEECS Log Number TVCG-2009-10-0240.
Digital Object Identifier no. 10.1109/TVCG.2010.110.
1077-2626/11/$26.00 ß2011 IEEE Published by the IEEE Computer Society
inria-00546158, version 2 - 28 Oct 2011
Author manuscript, published in "IEEE Transactions on Visualization and Computer Graphics 17, 7 (2011) 913-933"
DOI : 10.1109/TVCG.2010.110
We categorized the visualization techniques according
to their characteristics and features so as to make this
paper valuable both to academia and industry. One of our
goals is to help find promising new research directions and
select tools to tackle a specific concrete development issue,
related to the understanding of the static aspects of
software and its evolution.
Visualization of the static aspects of software can be split
into two main categories: visualization that gives a picture
of the software at time T on the one hand and visualization
that shows the evolution of software across versions on the
other hand. Both pertain to the static aspects of software but
the notion of time is added in the second category. In each
of these categories, we consider three levels of granularity,
based on the level of abstraction : source code level, middle
level (package, class or method level), and architecture level
[87], [88].
Our paper is organized as follows: In the first part
(Sections 2-4), we consider visualization of the static aspects
of software at time T. Section 2 presents visualization
techniques that help visualize source code at line level. In
Section 3, we discuss visualization techniques that provide
insight into classes and help understand their internals.
Section 4 deals with visualization techniques that focus on
visualizing three different architectural aspects of software.
The first (Section 4.1) looks at the overall source code’s
organization packages, classes, and methods. The second
(Section 4.2) looks at relationships between components, be
they based on inheritance or static call graph. The third
(Section 4.3) looks at metrics to visualize and manage the
quality of the software.
In the second part of our paper (Section 5), we present
the smaller number of visualization techniques dealing
with the evolution of the static aspects of software. This
part of the paper is organized in a similar way to the first
part. Section 5.1 thus presents visualization techniques that
help visualize source code line changes across versions. In
Section 5.2, we discuss visualization techniques that
provide insight into how classes evolve across versions of
the software. Section 5.3 deals with visualization techni-
ques that focus on visualizing two different architectural
aspects of software evolution. The first one (Section 5.3.1)
visualizes the overall source code organization changes.
The second one (Section 5.3.2) visualizes how software
metrics evolve. Note that we are not aware of any
visualization technique that focuses on visualizing how
relationships change across software versions. Finally, we
draw our conclusion in Section 6.
To help the reader, Table 1 provides a summary
overview of the classification of the visualization methods
and the section describing the method in our paper. The
table also specifies the year in which each method
appeared, thus helping to outline how the software
visualization field has evolved.
2CODE-LINE-CENTERED VISUALIZATION
This section deals with visualization at the source code line
level (see details in Section 2 in Table 1). Nevertheless, the
visualizations presented here have a higher degree of
914 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
TABLE 1
Synthetic View of Our Paper Organization and the Classification We Propose for Methods Visualizing the Static Aspects of Software
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abstraction than just displaying the source code itself.
Source code editors thus fall outside the scope of this
section and paper.
SeeSoft [1], [2] is a source-code-based visualization
technique by Eick and coworkers. This visualization
technique is a miniaturized representation of the source
code lines of the software. A line of code is represented by a
colored line with a height of one pixel and a length
proportional to the length of the code line. Indentation of
the code is preserved so the structure of the source code
stays visible even when a large volume of code is displayed.
To fill the window and to display large quantities of source
code simultaneously, a line of code can be represented by a
single colored square (Fig. 1a). This square representation
reduces the visualization of the source code to a minimum,
allowing the visualization of several source code files at a
time by placing their representations side-by-side, thus
providing rapid access to the overall source code of the
software in a single view.
Marcus et al. [3], [4] based their visualization technique
on SeeSoft and added a third dimension to create the sv3D
visualization technique. The latter maps each line of source
code to a rectangular cuboid in the same manner as the SeeSoft
visualization technique. Files are represented as a group of
rectangular cuboids placed on a 2D surface (Fig. 1b). To
visualize the entire software, groups of rectangular cuboids
(classes) are positioned in a 3D space. With this third
dimension, sv3D is richer in terms of actions and interactions
than SeeSoft. Users can move and rotate groups of cuboids to
arrange the visualization as they wish. Zooming provides an
efficient way to focus on a precise part of the visualization.
The displayed information can be filtered and managed by
adding transparency [89] or dispersing and regrouping
rectangular cuboids of the same color at distinct heights.
The color of each pixel corresponds to a particular
characteristic of the source code line. In both Figs. 1a and
1b, the color shows the type of source code line control
structure. The developer is generally able to mentally re-map
colored pixels to lines of code, which helps navigate through
the source code. Various mappings are possible, for instance,
the age of the line can be represented by a red (most recent) to
blue (oldest) color scale. The creators of SeeSoft mentioned
that even though individual colored squares are small, their
color is perceivable and often follows a regular pattern.
In the sv3D visualization technique, the third dimension
enables mapping of more source code line numerical
properties. This visualization technique is very expressive
because of the large number of visual parameters available
to display information (height, depth, shape, x-position, y-
position, and color above and below the Z axis). However,
the simultaneous displaying of all the available visual
parameters is likely to lead to an information overload and
to fail to effectively represent the software. Balancing
expressiveness and effectiveness is thus a very important
criterion to obtain an understandable visualization techni-
que [90]. In Fig. 1b, the height of the cuboid represents the
nesting level of the control structure (the higher the cuboid,
the higher the nesting). This mapping uses few parameters
to avoid a cognitive overload.
SeeSoft was used by Bell Laboratories during the 1990s
on a software containing millions of lines of code and
developed by thousands of software developers. Their
feedback on the Seesoft visualization technique was
positive [2]. They especially appreciated being able to have
both a global overview and a finely detailed view, by
simply moving the mouse over a colored pixel.
Comparing the two previous visualizations shows that
the SeeSoft visualization technique cannot display the
control structure’s nesting level at the same time as the
control structure itself. sv3D, on the other hand, is able to
show both the nesting level and the control structure by
using the third dimension.
As far as we know, the sv3D visualization, introduced in
2003, was the last visualization of the static aspects of
software to directly map source code lines to a visual
representation. The more recent visualizations rely on
higher level representations, more loosely associated with
the source code lines.
3CLASS-CENTERED VISUALIZATION
In this section, we present a visualization technique that
helps understand the inner functioning of a class, alone or
in the context of its immediate inheritance hierarchy (see
details in Section 3 in Table 1).
Understanding the functioning of a single class helps
grasp the way in which larger parts of the overall system
work. Some research has been done on visualizing the
cohesion within a class [91]. Cohesion metrics describe the
degree of connectivity among software components and
indicate whether a system has been well designed. How-
ever, a cohesion metric (as a numerical value) is difficult to
define precisely and to quantify. Visualizing cohesion can
therefore be useful to detect several design problems and
give clues about the design quality.
The class blueprint [5], [6], [7] is a lightweight visualiza-
tion technique that displays the overall structure of a class,
the control flow among the methods of the class, and how
methods access attributes. This visualization technique was
introduced by Lanza and Ducasse.
The class blueprint (bottom left of Fig. 2) is divided into
five layers (left to right): initialization, interface, implemen-
tation, accessors, and attributes. Methods and attributes are
represented as nodes placed in the layer they have been
assigned to. For instance, a method responsible for creating
an object and initializing its attributes is placed in the first
layer. Method invocation sequences are represented by
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 915
Fig. 1. (a) SeeSoft and (b) sv3D from [3].
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edges directed from left to right. Node size is mapped to
software metrics. Semantic information is mapped to the
colors of nodes and links (for instance, a red node is a
“getter” method).
The class blueprint visualization technique shows the
purpose of methods within a class and the relationship
between methods and attributes. It conveys information
that is otherwise hard to notice because that would require
a line-by-line understanding of the entire class. It also uses
metrics to show information pertaining to methods and
attributes. The metrics mapped to nodes corresponding to
attributes are the number of external accesses (width) and
number of internal accesses (height). The metrics mapped to
nodes corresponding to methods are the number of
invocations (width) and the number of lines of code
(LOC) in the method (height). All these metrics except
LOC are related to the coupling between modules in the
software and help locate modules that require the highest
maintenance effort.
With this visualization, visual patterns can be quickly
detected, which improves the understanding of the class.
Visual patterns use node size, distribution layers, node
color, edges, and the way the attributes of a class are
accessed. For example, in a class blueprint:
.several big methods can reveal an important class of
the system.
.a predominant interface layer means a class that acts
as an interface.
.many accessor methods (red) and many attributes
(blue) with few other methods describe a class that
mainly defines accessors to attributes.
.a cluster of methods structured in a deep, and often,
narrow invocation tree pattern means that the
developer has decomposed an implementation
(probably a complex algorithm) into methods that
invoke each other and, possibly, reuse some parts.
.attribute nodes that are accessed uniformly by
groups of method nodes reveal a certain cohesion
of the class regarding its state management since
multiple methods access the same state.
More examples can be found in [5], [6], [7].
Few available visualization tools cover class understand-
ing, like this one. Furthermore, the class blueprint visualiza-
tion technique supports class understanding within the
context of the immediate inheritance hierarchy, by display-
ing how a subclass fits within the context of its parent,
brothers, and children. Visual patterns in the context of
inheritance may thus be found as well. Experiments in [7]
have shown that the class blueprint visualization is useful to
better understand classes compared to source code reading.
4ARCHITECTURE VISUALIZATION
Visualizing the architecture of software [93] is one of the
most important topics in the visualization of software field
[86], [94], [95], [96]. Object-oriented software is generally
structured hierarchically, with packages containing sub-
packages, recursively, and with classes structured by
methods and attributes. Visualizing the architecture con-
sists in visualizing the hierarchy and the relationships
between software components. As is clear in Table 1, many
visualization techniques tackle the architecture level.
Being able to have a global overview of the system is
considered very important [97] to decide which components
need further investigation and to focus on a specific part of
the software without losing the overall visual context [18].
This section deals with representations of the overall
architecture, such as tree, graph, and diagram model
representations. We present visualization techniques focus-
ing on visualizing three different aspects of the software
architecture. First, the software global architecture, includ-
ing code source organization, to see how packages, classes,
and methods are organized. Second, relationships between
components, be they based on inheritance or call graphs.
Third, metric-centered visualizations to visualize the qual-
ity of the software. As we will detail, some representations
are better to visualize an aspect of software but less efficient
to visualize another.
4.1 Visualizing Software Organization
A tree model is perfect for representing packages, classes,
and methods organization. But the classic node-link
diagram is inappropriate for tree representation, quickly
becoming too large and making poor use of the available
display space (Fig. 3a). Moreover, the amount of textual
information contained in nodes should be limited because
too much will quickly clutter the display space, causing
information overload [87], [98]. For this reason, many tree
layout algorithms have been developed to optimize the
visual representation of the tree [99], [100], [101], [102].
These visualizations are mainly 2D representations but they
can be extended to 3D representations. This section presents
several visualization techniques that show the source code
organization. Most of them use tree representations that are
not specific to software visualization but are applied to
software (see details in Section 4.1 in Table 1, p. 2).
The Treemap visualization was introduced by Johnson and
Shneiderman [8], [9]. It provides an overall view of the entire
software hierarchy by efficiently using the display area [10]
(Fig. 3b). This visualization is generated by recursively
slicing a box into smaller boxes for each level of the
hierarchy, using horizontal and vertical slicing alternatively.
The resulting visualization displays all the elements of the
hierarchy, while the paths to these elements are implicitly
encoded by the Treemap nesting. Figs. 3a and 3b represent,
respectively, a common tree and its equivalent Treemap
(color helps understand the transformation mechanism).
916 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 2. Class Blueprint from [92].
inria-00546158, version 2 - 28 Oct 2011
Acircular Treemap is a visualization technique based on
nested circles, where circles contain subcategories in
smaller circles. Sibling nodes are at the same level and
share the same parent (Fig. 3c). Representing the hierarchy
using circles instead of rectangles makes it easier to see
groupings and hierarchical organization, because all the
edges and leaves of the original tree remain visible.
Different layouts have been studied to have circles
efficiently fill the available space [11].
Stasko and Zhang proposed the Sunburst visualization
technique [18], which is an alternative to nested geometry,
to represent tree models. This visualization technique relies
on a circular or radial display to represent the hierarchy
(Fig. 3d). It uses nested discs or portions of discs to
compactly visualize each level of the hierarchy [16], [17]. Its
main principle is that the deepest in the hierarchy is the
furthest from the center. The smallest disc at the center of
the visualization thus represents the root element, while the
child nodes are drawn further from the center within the arc
subtended by their parents. Experiments in [103] have
shown that the performance of typical tasks (such as
localization, comparison, and identification of files and
directories inside huge hierarchies) with a Sunburst and a
Treemap visualization is equivalent but the Sunburst is
easier to learn and more pleasant than a Treemap. The size
of packages, classes, and methods of the hierarchy are
represented in all techniques, i.e., Treemap, circular
Treemap, or Sunbust.
One drawback of the nested tree representation is that
elements are hard to differentiate. Research has therefore
been undertaken on a Treemap to explore the hypothesis of
giving irregular shape to the elements. This is the main idea
of the Voronoi Treemap [21] since various shapes allow a
much better differentiation than mere rectangles (Fig. 4).
Every package, class, and method will therefore have its
own unique shape.
Another drawback of a Treemap is that the implicit
hierarchical structure is hard to discern. To help distinguish
the structure level in the Voronoi Treemap visualization,
elements high in the hierarchy are colored dark red while
objects further down the hierarchy are blurred (Fig. 4). A
Shadowed Cushions Treemap [104] is another visual
technique designed to provide a better insight into the
internal structure of the Treemap. Experiments in [105]
have shown that users prefer interacting with this sha-
dowed cushion Treemap and are faster in performing a
substructure identification.
Some works aim to represent a Treemap and a circular
Treemap in three dimensions by displaying the substruc-
ture at different levels of elevation in the 3D space [106],
[107], [108], [109]. A circular Treemap can be displayed in
3D by turning circles into cylinders [11] and by linking the
height of each cylinder with the depth of the element in the
hierarchy (Fig. 5). Experiments in [107], [108] have shown
that 3D Treemaps are better than 2D Treemaps to visualize
depth in the hierarchy. Like a 3D Treemap, the 3D circular
Treemap provides a better perception of the depth of
elements in the tree. The notion of depth of elements in the
tree is linked to the height of cylinders in the 3D
visualization (Fig. 5d).
Storey et al. developed the Simple Hierarchical Multi-
perspective (SHriMP) tool [110], [111], [112]. SHriMP
combines several graphical high-level visualizations with
textual lower level views to ease navigation within large
and complex software (Fig. 6). In fact, SHriMP regroups a
set of visualization techniques among which the user can
easily switch depending on his/her needs. Fig. 6 shows a
Treemap visualization technique to display the software
organization in a single window. Colored boxes represent
packages (yellow), classes (light green), methods (green and
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 917
Fig. 4. Voronoi Treemap from [21]. Fig. 5. (a) Level 0. (b) Level 1. (c) Level 2. (d) 3D view.
Fig. 3. (a) Node-link diagrams. (b) Treemap. (c) Circular Treemap. (d) Sunburst. These figures display the same system.
inria-00546158, version 2 - 28 Oct 2011
blue), and attributes (red). The most interesting feature is
that each box can display its corresponding source code.
This feature makes it possible to have both the source code
organization and a miniaturized view of the source code
itself in a single visualization. Documentation can be seen in
the same way.
To ease browsing source code, SHriMP features a
hypertext browsing technique on object types, attributes,
and methods. The hyperlinks can be used to navigate over
the source code using animated translation and zooming
motions over the software visualization. The fully zoomable
interface of SHriMP supports three zooming approaches:
geometric, semantic, and fisheye zooming. Geometric
zooming consists in scaling a specific node in the nested
graph while hiding information in the rest of the system.
Fisheye zooming [113] allows the user to zoom in on a
particular piece of the software, while simultaneously
shrinking the rest of the graph to preserve contextual
information. Semantic zooming displays a particular view
inside a node depending on the task at hand.
With all these features, SHriMP is a very good visualiza-
tion tool to explore software structures and browse
program source code. Human cognitive and perceptual
capabilities are effectively exploited using smooth, inter-
active animations to show the part of the hierarchy focused
upon. These animations allow the human perceptual
system to immediately track the position of the software
component focused upon [68]. This technique represents a
lower cognitive burden than if the selected part is just
highlighted without animated transition. In addition,
according to [114], [115], it makes the visualization more
understandable and more enjoyable.
SHriMP views have been very successful and integrated
into several systems [116] such as the Rigi reverse engineer-
ing environment, which significantly impacted research
tools and industry [117], [118], [119]. Experiments in [56]
have shown that the ability to switch seamlessly between
visualization techniques, as well as regrouping code, doc-
umentation, and graphical high-level views, were useful
features to ease navigation and software understanding. A
visualization that focuses on facilitating source code ex-
ploration can indeed enhance development and mainte-
nance activities.
Visualizing software, using a real-world metaphor, consists
in representing software with a familiar context, by using
graphic conventions the user immediately understands [14],
[89], [120], [121], [122]. According to Dos Santos et al. [123],
this technique allows faster recognition of the global
software structure and better and faster understanding of
complex situations, preventing the most problematic aspect
of 3D software visualization, i.e., disorientation. Visualiza-
tion based on real-world metaphors relies on the human
natural understanding of the physical world, including
spatial factors in perception and navigation.
In 1993, Dieberger proposed to represent information as
aCity metaphor to solve the navigation problem [12], [13],
[124]. In our paper, we use the term City metaphor when the
whole software is represented by a single city whose
buildings represent classes, whereas, we created the term
Cities metaphor when the whole software is represented by
several cities. In the Cities metaphor, the cities can represent
packages (where buildings symbolize classes) or classes
(where the buildings symbolize methods).
Our world, as it is structured [125], provides a natural
way of splitting elements into subelements. For instance,
the Earth is divided into countries, countries into cities,
cities into districts, and districts contain streets, buildings,
gardens, and monuments that themselves comprise build-
ings and gardens. These different degrees of granularity are
used as an analogy for the software hierarchy. For instance,
in a possible mapping, the Earth represents the overall
system, countries packages, cities files, districts classes, and
buildings methods. This kind of software visualization
provides a large-scale understanding of the overall system.
Knight and Munro [126] were the first to try representing
software as Cities. They named their visualization “The
Software World” [14], [127].
Panas et al. [15], developed a very detailed Cities
metaphor to represent software. Their metaphor is as close
as possible to real cities, with an extremely detailed and
realistic visualization, with trees, streets, street lamps (Fig. 7).
By doing this, the authors intend to enable a very intuitive
interpretation of a software system. The user is free to zoom
and navigate through the city representing the software.
It is strongly believed that real-world metaphors do not
have to correspond exactly with reality and that small
discrepancies do not hinder understanding. In fact, we
consider that small discrepancies, especially simplification
of the reality, can help focus on the important information
of the visualization.
Graham et al. proposed another real-world metaphor to
represent software: the Solar system [19], [20]. This
918 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 6. The Treemap visualization from the SHriMP application.
Fig. 7. Realistic City metaphor representing software from [15].
inria-00546158, version 2 - 28 Oct 2011
visualization represents the software as a virtual galaxy
made up of many solar systems (Fig. 8). Each solar system
represents an entire package. Its central star is an icon that
symbolizes the package itself, while planets, in orbit
around it, represent classes within the package. The orbit
level indicates the depth of a class in the inheritance tree:
the farther from the star, the deeper in the inheritance tree.
Blue planets represent classes, light blue planets interfaces.
Solar systems are shown as a circular formation to improve
readability, but the position of planets and solar systems
can be moved by the user, which is a very interesting
feature that few visualizations offer.
The Solar System metaphor has several interesting
properties but if we compare the two real-world metaphors,
it could be argued that the Solar System metaphor offers
fewer levels to represent the organization of software
source code. Broadening the Solar System metaphor to a
Universe metaphor could, nonetheless, offer extra levels to
represent packages brought together within upper-
packages symbolized by Galaxies.
4.2 Visualizing Relationships in the Software
Visualizing relationships in the software is a harder task
than visualizing the software hierarchy, because compo-
nents can have a much larger number of relations of many
kinds, such as inheritance, method calls, accesses (see
details in Section 4.2 in Table 1, p. 2).
Graphs have all the characteristics needed to represent
relationships between components by considering software
items as nodes and relationships as edges [128], [129], [130],
[131], [132]. However, visualizing all software relationships
can be equivalent to visualizing a huge graph with many
different interconnections, especially for large software
applications. The resulting visual representation can thus
be very confusing, with plenty of edge congestions, over-
lapping, and occlusions, which makes it almost impossible
to investigate an individual node or edge.
A solution to avoid cluttered 2D graphs is 3D represen-
tation of the graphs [133], [134]. With 3D, the user can
navigate to find a view without occlusions. However,
navigation through a 3D graph is difficult and quickly
disorientating, sometimes requiring that navigation be
started again from scratch [123]. Solutions have been
proposed, such as restricting the user’s navigation freedom
[135], or by generating automatic camera paths through the
3D graph [136].
One visual alternative to the node-link representation of
graphs is a square matrix with identical row and column
labels. The number of relations between a row element and
a column element is shown in the matrix. Also called the
Dependency Structure Matrix (DSM) [22], [23], [24], it
provides a simple, compact, and visual representation of
relations in a complex system. This technique has been
successfully applied to identify software dependencies
among packages and subsystems. DSM has been enriched
with more visual information to identify cycles [137], [138],
and class coupling [139].
UML class diagrams are probably the most popular graph-
based software visualization. Their purpose is to display
inter-class relations, such as inheritance, generalization,
associations, aggregations, and composition. Like other
graphs, when UML class diagrams grow, they become
gradually visually complex and prone to information
overload (Fig. 9a).
One way to reduce the visual complexity of a UML class
diagrams is to reduce the number of overlapping edges. But
this is not the only criterion, some studies [140], [141] point
out some important esthetic preferences such as the use of
an orthogonal layout (produces compact drawings with no
overlap, few crossings, and few bends), the horizontal
writing of the labels, the join of inheritance edges that have
the same target, correctly labeled edge.
To do this, the GoVisual UML visualization takes into
account esthetic preferences [25] (Fig. 9b) to provide a better
perception, by drawing generalization relationships within
the same class hierarchy in the same direction, avoiding
nesting of class hierarchies, and using colors to highlight
distinct class hierarchies and generalizations. Fig. 9b is
obviously more understandable than Fig. 9a, which con-
firms that esthetic preferences described above are very
important [142].
UML class diagrams were originally created to be drawn
on 2D surfaces. Several works represent UML diagrams in
3D, using the third coordinate to display more information
[26], [27], [28].
Irani et al. used geon diagrams to represent UML class
diagrams 10(a) [143], [144]. Geons are object primitives
consisting of 3D solids, such as cones, cylinders, and
ellipsoids, along with information about how they are
interconnected. The technique is based on an elaborate theory
of structural object recognition by Biederman [59], which
suggests that if the information structure can be mapped onto
structured objects then the structure will be automatically
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 919
Fig. 8. Solar System metaphor from [19].
Fig. 9. (a) Classical Layout. (b) GoVisual Layout from [25].
inria-00546158, version 2 - 28 Oct 2011
extracted as part of normal perception [58]. An interesting
characteristic of the geon diagram is that color and texture
play a secondary role in perceptual object recognition, so they
can be used to represent secondary characteristics. In
Figs. 10a and 10b, we can see a UML class diagram and its
equivalent geon diagram. Any UML class diagram can be
turned into its equivalent geon diagram [145].
Several experiments in [146] showed that a geon diagram
is both easier to understand and easier to remember than
traditional UML class diagrams because of the use of simple
3D primitives.
We have already described in Section 4.1 the SHriMP
multi-view visualization tool. SHriMP also embeds some
visualization techniques to display relationships in the
software.
One of them shows the static call graph of the software,
representing methods by boxes and calls between methods
by edges (Fig. 11). The source code of the method can thus
be seen without losing the call graph context, which is very
convenient to understand communications between meth-
ods. The hypertext browsing and zooming, explained in
Section 4.1, are still valid for this visualization technique.
Another visualization technique, embedded in SHriMP,
aims at showing every relationship in the software at once.
Fig. 12 features a nested graph representing the source code
hierarchy. The technique used is very similar to the SHriMP
source code organization visualization described in Sec-
tion 4. Relationships are directly visible as colored arcs
layered over the nested graph. Arcs are labeled with the
text: “extends by,” “implemented by,” “is type of,” “calls,”
“accesses,” “creates,” “has return type,” “has parameter
type,” “cast to type.” Fig. 12 shows that a box can be turned
into a source code editor on demand, without loosing the
high-level visualization.
Since displaying many arcs over a nested graph can lead
to confusion, work has been done to reduce this visual
complexity by filtering features to keep only the nodes and
links that are needed to answer a specific question (e.g.,
display only “calls” edges that target package A)[147].
The Extravis tool uses a Hierarchical Edge Bundles
visualization technique to visualize hierarchical and non-
hierarchical relationships of the software created by Holten
[31]. The main idea is to display connections between items
on top of a hierarchical representation. Fig. 13 shows a
software system and its associated static call graph. Soft-
ware elements are placed on concentric circles according to
their depth in the hierarchical tree. The edges are displayed
above the hierarchical visualization, and represent the
actual call graph. The same technique can be used on top
of other visualizations of the hierarchy, such as Treemaps,
circular trees, and others.
Some studies use spline edges to naturally indicate the
relationship direction with no explicit arrow [148]. The
Hierarchical Edge Bundles use a color interpolation on
edges to represent the communication direction from caller
(green) to callee (red). Thus, Fig. 13 shows that the packages
at the bottom receive many calls from other packages.
To reduce the visual clutter and edge congestion, [149]
bundles edge together by bending them. The edge bundling
strength is controlled by a parameter, which alters the
920 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 10. (a) UML diagram. (b) Equivalent geon diagram.
Fig. 11. Call graph visualization from the SHriMP application.
Fig. 12. Nested boxes visualization from SHriMP.
Fig. 13. Hierarchical Edge Bundles from [31]. (a) ¼0. (b) ¼0:75.
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shape of the spline edges (Fig. 13). Ambiguity problems are
thus partially resolved, and relationships between compo-
nents can be displayed in a better manner. The visualization
also allows selecting a specific edge for further inspection.
To emphasize short edges, individual edges and sub-
groups of edges, visual alpha blending is used to draw long
edges at lower opacity than short edges. This result
provides an efficient rendering for visualization of edges.
Experiments in [31] show that the majority of the
participants regarded the technique as useful for quickly
gaining insight into class relationships. In general, the
visualization was also found esthetically pleasing. Hierarch-
ical Edge Bundles can be displayed on top of many different
hierarchical structure representations but most participants
preferred the radial layout over the other alternatives.
The City or Cities metaphors can also be used to depict
relationships. The Cities visualization, presented in Sec-
tion 4.1, proposes a “satellite view” to observe the cities from
above. From this point of view, the user sees cities
(packages) connected via streets and water. Streets represent
two-directional calls between packages. Water shows uni-
directional calls. Clouds cover cities that are not of current
interest to the user, which provides a realistic way of
filtering information.
Alam and Dugerdil proposed another way to visualize
relationships with a City metaphor. Their visualization
technique named Evospaces [32], [33] displays relationships
as solid curved pipes between buildings (classes) or
between objects inside buildings (methods). A colored
segment moving along a pipe suggests the direction of the
relation from the origin to the destination (Fig. 14). For
instance, if the user wants to display call relationships of a
selected class, pipes will be drawn from the selected
building, and segments will move to callee classes. Curved
pipes are used instead of straight ones to avoid overlapping
and visual occlusions.
Textured buildings increase the feeling of navigating
through a real city. This visualization provides more details
when focusing on a class. The user can enter a building and
see that it contains objects representing methods and local
variables. Like for buildings, relationships can be displayed
at method level.
Evospaces allow many interactions, such as seeing metric
values, changing the appearance of objects, opening the
corresponding source code file, etc. To reduce disorientation,
a 2D minimap can be displayed in a corner of the screen to
show the user current position in the city. This combination
of 3D and 2D views helps the user make precise situation
assessments for his/her navigation [150].
Panas et al. [34] use a Cities metaphor to represent
software. We name it “The Unified Single-View City.” In their
visualization (Fig. 15), methods are represented by build-
ings, which are placed on blue plates that symbolize classes.
These blue plates are spread on green plates that represent
packages. The height of a green plate (package) depends on
the depth of the package in the hierarchy, which creates
virtual mountains. The resulting visualization looks like an
Island metaphor, with sky and water between islands added
for better esthetics.
Relationships between components are represented by
several graphs that can be displayed alone or simulta-
neously. Available graphs comprise function calls, class
calls, and class inheritance. Since cities are placed on plates,
the resulting visualization looks like a graph with cities
drawn on each node. The fact that plates are positioned on
several planes, eases the display of relationships.
The visualization of Fig. 15 was created with the Vizz3d
tool [151], [152]. Vizz3d helps create new representations by
defining only graphical objects and the mapping, instead of
hard-coding them. Vizz3D is very versatile, and the
resulting visualizations can be completely different.
One drawback of City and Cities metaphors is that they
can only be laid out on a two-dimensional plane that makes
displaying relationships between components problematic.
A solution could be walkways or roads. However, placing
buildings to minimize roadways overlapping is a compli-
cated task [19]. The Unified Single-View City tries to solve
this by putting cities on several planes at different heights.
With the 3D Solar System layout presented in Section 4.1,
relationships can be more efficiently displayed (Fig. 8),
because every Solar System can be moved (in the 3D space)
to avoid crossing edges. The Solar system visualization
technique may display relationships, such as coupling and
inheritance, using colored edges. This has no real-world
connection but does not distort the user’s understanding
(Fig. 8). Nevertheless, if too many relations are displayed
simultaneously, the visualization and 3D graph representa-
tion would be unclear. The authors of the 3D Solar system
thought that using gravity to represent coupling seems a
little too esoteric.
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 921
Fig. 14. Evospaces visualization from [33].
Fig. 15. The Cities and Island metaphor from [34].
inria-00546158, version 2 - 28 Oct 2011
Balzer and Deussen proposed the Software landscape
metaphor [29], [30] that can be considered a hybrid metaphor
borrowing from the Solar system, the Island and the Cities
metaphors. Its authors use 3D nested hemispheres to
represent package hierarchy (Fig. 16). The outermost hemi-
sphere represents the root package, and it contains hemi-
spheres corresponding to the packages that are directly
contained in the root package. Classes are represented as
circles on a platform representing its package, while
methods and attributes are displayed as simple colored
boxes on the circle (Fig. 16a).
Another interesting point is how the Software landscape
metaphor represents relationships between components,
with a Hierarchical net technique. The idea is to route
relationship links according to the hierarchy levels in the
software (Fig. 16b). The edges of objects from a hierarchy
level are grouped together and forwarded to the next (higher)
level. The resulting visualization looks like a 3D tree with no
overlap. This technique avoids overlapping but makes
tracking a single edge difficult. Various kinds of relationships
can be shown by using colors to represent the connection,
whose size indicates the number of relationships.
Soon after the Software Landscape visualization, Balzer
and Deussen [35] developed another 3D visualization also
based on a clustered graph layout, to display large and
complex graphs (Fig. 17). Their technique uses clustering,
dynamic transparency, and edge bundling to visualize a
graph without altering its structure or layout. The main idea
is to group remote vertices and classes into clusters. The
contents of a cluster are visible when the user focuses on a
subpart of the graph, without being bothered with the
details of distant clusters. The degree of transparency is
dynamically adapted to the viewer location [153]. The
nearer the viewer, the more transparent the cluster, with the
most remote ones hiding their contents. This is a very
interesting feature, because it allows a comprehensible
interactive visualization of large systems with detailed
information on focused parts. In addition, edges are routed
and bundled together visually as one port of communica-
tion between two clusters, which makes it easier to track an
individual edge. An edge shows more details when the user
view is focused on it.
The visibility of nodes and links is thus changing
continuously, with smooth transitions in terms of detail
levels while navigating through the visualization, which
makes large graphs manageable. Fig. 17 shows a graph with
more than 1,500 nodes and 1,800 edges within 126 clusters,
representing the inheritance relationships between classes
of a large piece of software.
The clustered graph layout produces a more compre-
hensible representation of complex graphs. The example in
Fig. 17 shows inheritance relationships, but another inter-
esting use of this technique is to represent coupling between
classes. Since coupled classes are likely to be considered
together during development, these classes are placed close
to one another in the 3D space, so as to be considered as a
big cluster.
4.3 Metric-Centered Visualization
A software metric is a numeric measure of some property of
a piece of software or its specifications [154], [155], [156],
[157], [158]. Its purpose is to quantify a particular
characteristic of a software. Software metrics are interesting
because they provide information about the quality of the
software design [159], [160], [161] and provide ways to
monitor this quality throughout the development process
[162]. Static software metrics effectively describe various
aspects of complex systems, e.g., system stability, resource
usage, and design complexity.
The visualization of software can transform the numer-
ical data provided by metrics into a visual form that
enables users to conceptualize and better understand the
information [70], [163], [164]. The main challenge is to find
effective mappings from software metrics to graphical
representations [165].
In this section, we describe several visualization techni-
ques that use static software metrics. Most of these
visualization techniques use an existing visualization but
properties on graphical elements are related to software
metrics. For instance, a software metric related to the size of
the software component can be mapped to the size of the
graphical elements (see details in Section 4.3 in Table 1, p. 2).
Software metrics can effectively describe various aspects
of complex architectures, and are thus worth combining
with UML class diagrams. UML class diagrams provide a
representation of the software design but they show little
information. Termeer et al. [38] proposed the MetricView
visualization that displays metric icons on top of UML
diagram elements (Fig. 18) [36]. Bar and pie charts are
mapped to metric values, in a configurable way. A 3D
mode of this visualization is available just by turning 2D
bars in 3D cuboids.
922 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 16. (a) 3D nested spheres from [29]. (b) Hierarchical net from [30].
Fig. 17. Clustered graph layout from [35].
inria-00546158, version 2 - 28 Oct 2011
The main drawback of this technique is the occlusion of
the diagram by the icons, especially with 3D icons. This can
be partially solved by using sliders to control the transpar-
ency of the UML diagram and the metric icons.
Instead of drawing icons on top of UML elements, Byelas
and Telea [44], [45] developed a method named area of
interest (AOI) that brings together software elements that
share some common properties (Fig. 19) by building a
contour that encloses these elements, and by adding colors
within the AOI to display software metrics. The AOIs are
shown on top of the UML class diagrams without changing
its layout, to prevent disorientation.
Each AOI has its own texture such as horizontal lines,
vertical lines, diagonal lines, and circles. These simple
textures differentiate better when they overlap, creating a
visually different pattern. Visual techniques, such as
shading and transparency, are also used for a better
perception of several areas, thus minimizing the visual
clutter. One different metric can be associated to each AOI
and its value is added to the texture using a red (high) to
blue (low) color scale. This helps to show how metric values
change over one AOI. When AOIs overlap, the color
information for each AOI still can be seen on the texture.
The system shown in Fig. 19, represents over 50 classes
with seven areas of interest. Here, the AOIs regroup classes
that have a high level functional property in common, for
instance classes containing the user interface code (A1:
GUI), classes that are the application entry point (A5:main),
and classes containing the application control code (A6:
core). Byelas and Telea defined the participation degree pi;j
of a class Cjin an area Aias the code percentage of Cj
specific to Ai: an OpenGL class has p¼0:5if it has 50
percent OpenGL-specific code. The authors consider that
their participation degree metric helps understand how the
identified property maps to actual classes, i.e., whether the
code follows the intended design, and whether there are
modularity problems.
Several facts can be noticed from Fig. 19:
.Few AOI overlap, so few classes participate in two
high level functional properties, and none takes part
in three, which indicates a good functional mod-
ularity.
.The B class is over a red color in A5 and A6, so the
class is strongly involved in two different AOIs.
.The E class is over a red color in A6 and a blue color
in A1, so the class participates strongly in the former
and weakly in the latter.
Authors have mentioned that if more than three AOIs
overlap then information becomes hard to understand.
Nevertheless their visualization can show up to 10 areas of
interest, each with its own metric, on a diagram of up to 80
classes. However, we think this visualization may be prone to
eyestrain because of the large number of colors and textures.
Polymetric views [5], [36], [37], created by Lanza et al., is a
lightweight visualization of software enriched with soft-
ware metrics (Fig. 20). They implemented this technique in
the “CodeCrawler” tool [166] built on top of the Moose
reengineering framework [167], [168]. This visualization
technique is also available as a stand-alone tool and as an an
open-source software visualization plug-in for the Eclipse
framework. Polymetric views propose a completely config-
urable graph-based representation to create multiple visua-
lizations, depending entirely on the mapping between
metrics and visual characteristics. The authors wanted to
have a very clear definition of each metric, so only direct
ones are available, which means that their computation
does not depend upon another metric [169].
All the graph characteristics are based on metrics that
define node width, height, x and y-coordinates and color,
and edge width and color. This freedom of mapping makes it
possible to visualize several aspects of the software, using the
most appropriate visualization. For instance, Fig. 20a shows
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 923
Fig. 19. Areas Of Interest from [45].
Fig. 20. Polymetric views from [36]: (a) Inheritance Tree. (b) Correlation
graph.
Fig. 18. (a) MetricView height bars. (b) MetricView pie charts.
inria-00546158, version 2 - 28 Oct 2011
an inheritance tree where nodes represent classes and edges
represent the inheritance relationship between them. Node
width and height represent the number of all descendants of
the class and the number of methods in the class, respec-
tively. Node color is used to represent the number of
immediate children. The goal of this mapping is to show
how classes share methods through the inheritance hier-
archy. Fig. 20a shows that mand nseem to be well designed
because every subclass is higher than it is wide, which means
they inherit parent methods and have not many immediate
children. On the contrary, oand pare small, wide, and black,
because they have few methods and many immediate
children that are at the end of the inheritance hierarchy.
In Fig. 20b, nodes represent methods, while both node
color and x-coordinate represent the number of code lines.
The y-coordinate node represents the number of statements.
This mapping provides a method size overview, to detect
empty methods and very big methods. Fig. 20b shows that
method Odoes not include any statement, and method N
contains several lines of code but no statement at all. These
methods have to be checked further and maybe deleted. In
contrast, method Phas more statements than lines of code,
which indicates bad code formatting. Class M, that has
many statements and lines of code, seems to be a good
candidate for a split.
Other visualization techniques, such as histogram,
checker, staple, confrontation, circle, and others, can be
designed in a similar way [5], [36], [37].
Holten et al. used texture and color to show two software
metrics on a Treemap (Fig. 21) [39]. This choice is based on
the fact that human visual perception enables rapid
processing of texture [170]. The authors used the color
range to visualize one software metric and a synthesized
texture distortion to visualize another one. The use of these
two visual characteristics provides a high information
density, helps find correlation between metrics, and can
reveal interesting patterns and potential problem areas.
In Fig. 21, methods are the deepest level of the hierarchy
and are visualized as boxes, while packages and classes are
implicitly represented (see Section 4.1). This mapping is
composed of two metrics:
.the number of callers (FANIN) is shown by a color
scale white-pink-red-black.
.the number of callees (FANOUT) is represented by a
texture distortion scale. The higher the metric, the
more distorted the texture.
In the object-oriented paradigm, it is generally desirable
that methods with high FANIN (critical methods) have low
FANOUT to keep them from depending on too many other
methods. The first ellipsis from the top shows methods with
high FANIN and low FANOUT. The second ellipsis shows
methods with low FANIN and high FANOUT. The third
shows methods with fairly high FANIN and medium
FANOUT, which may reveal a design issue.
Langelier et al. [40] think that the simplicity of the chosen
visual representation is crucial for human perception. Their
visualization, named “VERSO,”usessimpleboxesto
represent classes, and cylinders for interfaces (Fig. 22). The
human visual system is a pattern seeker of enormous power
and subtlety [164], and relying on these simple shapes
fosters a better and faster recognition of the underlying
information without overloading the visualization.
Three graphical properties of the boxes (height, color,
and angle) can be used to represent metrics. Although any
metric can be mapped to any of the properties, the default
mappings have the following underlying semantics:
.Box height is naturally related to code size.
.Box color is related to coupling. Since red is
associated with danger, red symbolizes high cou-
pling, which is dangerous in the object-oriented
paradigm.
.Box angle represents the lack of cohesion, because
twisted boxes look more chaotic.
The software architecture is shown either by a Treemap
or a sunburst layout (Section 4) representing the package
hierarchy, while classes are represented by boxes within
their package.
The inheritance hierarchy is not represented but the user
can select a class and see classes that have an inheritance
relationship with it. Several types of relationships are
available such as “in,” “out,” and “in/out,” “aggregation,”
“generalization,” “implementation,” “invocation.” The vi-
sual importance of useless elements can be reduced to focus
on a subset of elements. A global view of the system is kept
by only modifying the colors of filtered boxes. Filters are
based on metric values or inheritance relationships.
This visualization places the human at the center of the
decision process to help semiautomatically detect anomalies
that are tricky to fully automatically detect [41]. One
example is the detection of a Blob antipattern [171], which
requires checking numerous criteria. Indeed a Blob class is a
924 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 21. Treemap with color and texture from [39].
Fig. 22. VERSO from [40].
inria-00546158, version 2 - 28 Oct 2011
class that has a high complexity, low cohesion, and whose
classes related by an “out” association have little complex-
ity, high cohesion and are deep in the inheritance tree. To
help detect a Blob, complexity is first mapped to height,
lack of cohesion is mapped to twist, and depth in the
inheritance tree is mapped to color. A filter is then applied
to select only the classes with a very high level of
complexity (to reduce the search space, classes with an
extremely high value are colored in black). Then twisted
classes are checked to identify potential suspects. Finally, a
filter is applied on each potential Blob to see if associated
“out” classes are small (low complexity), straight (high
cohesion), and blue (deep in the inheritance tree). If so, the
selected class is indeed a Blob antipattern.
The process to find design anomalies may be a bit complex
but Dhambri et al. point out some important facts about
automatic design anomaly detection [41]. First, there is no
consensus on how to decide whether a particular design
violates a quality heuristic. Second, detecting dozens of
anomaly candidates is not helpful, if they contain many false
positives. The authors said that the detection is more effective
and useful when it is seen as an inspection task supported by
a software visualization tool. We agree. Experiments in [41]
confirmed that using VERSO to find anomalies is easier than
manual inspection, and that the variability of the number of
anomalies detected is lower when using VERSO than when
conducting a full manual search.
CodeCity is a visualization tool proposed by Wettel and
Lanza that represents the software with a City metaphor [42].
This visualization is also available as a stand-alone tool and
as an an open-source 3D software visualization plug-in for
Eclipse. CodeCity displays classes as buildings, and
packages as city districts. Classes within the same package
are grouped together, using a Treemap layout to slice the
city into districts (Fig. 23).
Another idea to define building location in the city is
proposed in [15]. The authors chose the amount of coupling
between software components to determine building layout:
the closer the buildings, the higher the coupling. This layout
is interesting, because seeing coupling this way is very
intuitive and very efficient for detecting problematic areas
within the software. But the overall layout may drastically
change between versions, which confuses the user [172].
In CodeCity, many metrics can be mapped to city
characteristics. The default mapping creates an intuitive
semantic mapping that helps reason about the system. The
Number Of Methods (NOM) metric is mapped to building
height, thus showing the amount of functionality in classes,
while the Number Of Attributes (NOA) metric is repre-
sented as the width of a building. A class with many
methods, but few attributes, is thus represented as a tall and
thin building, whereas a class with a large number of
attributes and few methods appears as a platform. The
authors claim that this visualization reveals big and thin
class extremes, and also gives a feeling of the magnitude of
the system and the distribution of the system intelligence.
However, the resulting city looks unrealistic because
very diverse building shapes appear. This is problematic
because it goes against the gestalt principles [173] that
state that humans efficiently distinguish at most six
different shapes. The authors [174] think that having only
five different building heights can reduce the cognitive
load, because humans tend to organize visual elements
into groups or patterns when objects look alike [175].
Moreover, using only five different heights of building
decreases the visual complexity and makes a more
realistic and familiar city, hence easing navigation. In
the EvoSpace visualization (Section 4.2), the authors push
this principle a bit further by accentuating the differences
with textures on buildings. The textures used from the
smallest kind of building to the highest are: house texture,
city hall texture, apartment block texture, and office
buildings texture (Fig. 14).
The color and transparency of several buildings can be
changed by the user to visually focus on a subset of
buildings. The point of view can be moved around the
visualization with a high degree of freedom, but to limit
disorientation, it is not possible to pass through buildings or
go underground.
The CodeCity visualization helps detect high-level de-
sign problems, using software metrics [43]. Classes with
design issues are singled out by coloring their representa-
tive building with a vivid color corresponding to the issue.
This creates a visual “disharmonies map” of the city,
providing a way to focus on problematic classes (Fig. 23).
CodeCity also features a finer-grained representation that
extends the previous one by explicitly depicting the methods
[43]. Each building is now composed of a set of bricks
representing methods within the class. The disharmonies
map can be shown at the method-level, and thus provide a
very precise localization of design problems (Fig. 24).
Other techniques to spot potential design issues have
been proposed. In the realistic City metaphor presented in
Section 4.1, the authors of [15] mapped building texture to
a metric related to the quality of the class source code. Old
and collapsed buildings indicate source code that needs to
be refactored, which is a realistic and intuitive way to
indicate design problems. A second technique, the
CocoViz” visualization proposed by Boccuzzo and Gall
[176], [177], focuses on visualizing whether a system is
well-designed or not. Their main idea is that misshaped
objects symbolize potentially badly designed software
elements. In addition, misshaped objects draw attention;
so they are very easy to spot. Simplified 3D real objects
represent classes. For instance, the house metaphor is
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 925
Fig. 23. CodeCity class-level disharmonies map from [43].
inria-00546158, version 2 - 28 Oct 2011
composed of a cone for the roof and a cylinder for the
body. Each visual characteristic of these two objects may
represent a normalized software metric. If the house is out
of proportion, then the class may have a design problem.
In the Cities and Island metaphor presented in Section 4.2,
the authors claimed that showing a lot of information in a
single view was better than in multiple views [67], because a
single view is easier to navigate through and always
presents the same familiar picture of the system. Their
visualization thus displays a lot of information (architecture,
relationships, metrics) through a unique unified single-view
visualization [34] (Fig. 15).
As all available metrics have to be displayed in one
single view, the authors add 2D icons on top of each
building to convey information. The height, width, depth,
and texture of every visual object can express metrics as
well. This visualization technique thus provides a very
complete summary of the overall system but the underlying
problems of single view are information overload and
disorientation [67]. The key asset of this visualization, in
order to overcome information overload, is the use of the
cities metaphor to represent the structure of the system
architecture. However, no empirical experiments were
conducted on this visualization technique.
Nevertheless, we agree that the city metaphor is adapted
to implicitly represent the software structure and metrics,
displaying a lot of information at the same time.
On the contrary, the Solar system metaphor presented in
Section 4 can only show one metric at a time, because
planet size is the only parameter available to map a metric.
So the visualization is split into five modes, where five
different metrics are mapped to planet size: lines of code
(LOC), weighted methods per class (WMC), depth of
inheritance tree (DIT), number of children (NOC), and
coupling. These metrics are part of the well-known CK
metric set, which has been empirically validated as a good
quality indicator and as a useful predictor of fault-prone
classes [178], [179], [180]. In addition to mapping the
chosen metric to the planet size, the metric value is also
displayed as text under each planet. Filters can be applied
to the overall system to display only the planets that have
metric values within the defined interval.
5VISUALIZING SOFTWARE EVOLUTION
Visualizing software evolution is not easy because adding
the time dimension implies a lot of extra data. Nevertheless,
visualizing software evolution helps explain the current
state of the software and depict important changes such as
refactoring and growing modules [181], [182]. It provides
useful information such as the modules that have been
under heavy maintenance, or, on the contrary, barely
touched along their entire evolution [183].
The field of software evolution visualization also includes
visualizations to understand how different developers
interacted on various parts of the system [184], [185], [186].
This type of visualization will not be treated in this paper
because it falls beyond its scope, since we exclusively
consider the software itself and not its development process.
Most techniques to visualize evolution are based on a
static visualization technique, but show one “image” for
each version of the software and animate the transition
between them. Other types of visualization of the evolution
display the entire evolution in a single image.
This section about evolution follows the same pattern as
the previous parts of this paper. First, we present source code
evolution visualizations in Section 5.1. Section 5.2 then
tackles the visualization of single class evolution. Finally, we
look into architecture evolution visualization in Section 5.3.
5.1 Visualizing Source Code Line Changes
This section presents a visualization technique to understand
how the detailed structure of source code changes during
development (see details in Section 5.1 in Table 1, p. 2).
Telea et al. proposed the Code flows visualization
technique that displays source code line evolution across
file versions [46], [47]. Code flows look like a complex cable-
and-plug wiring metaphor (Fig. 25). They make it possible to
visually track a given code fragment throughout its
evolution with guaranteed visibility. It also highlights more
complex events such as code splits and merges (S and M in
Fig. 25). This level of details gives a lot of information and
means that it is possible to focus on the evolution of one
specific source code file. In Fig. 25, four versions of a source
code class are represented from left to right, using code
flows with an icicle layout [102]. Bundled edges show what
a specific source code line becomes in the next version of the
class. For more readability, source code lines that remain
the same are colored in black.
This visualization technique provides a good general
overview of a class code changes. It shows whether source
code changed significantly or remained unaltered. It can
display large classes with more than 6,000 lines.
926 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 25. Code flow from [47] (modified).
Fig. 24. CodeCity method-level disharmonies map from [43].
inria-00546158, version 2 - 28 Oct 2011
5.2 Visualizing Class Evolution
This section presents a visualization technique to under-
stand how class methods evolve with software releases (see
details in Section 5.2 in Table 1, p. 2).
Wettel and Lanza created the timeline visualization
technique to depict class evolution (Fig. 26). It relies on a
detailed Building metaphor where every building represents a
class and every brick represents a method. Each method
stays at the same spot across versions of the class; when the
method disappears, the spot remains empty. Color is used to
depict the age of methods, from light yellow for recent or
revised methods to dark blue for the most long-standing. The
age of a method is an integer value representing the number
of versions that the method “survived” up to that version.
The timeline visualization is very useful to show how
many methods the class defines and when new methods are
created and disappear. Some evolutionary patterns can be
found, for instance a building (class) that evolves and loses
an ever-increasing number of bricks (methods) looks
unstable. Another example is when a large number of
bricks are suddenly added from one version to another,
meaning that the class is becoming more important in the
software. Correlating the timeline visualizations of several
classes enables the detection of massive refactoring as well
as files that participate in the same change [187].
5.3 Visualizing Software Architecture Evolution
Visualizing the evolution of the software architecture is one
of the most important topics in the field of software evolution
visualization. Having a global overview of the entire system
evolution is considered very important, because it can
explain and document the current state of software design.
In this section, we present visualization techniques that
focus on visualizing three different aspects of the evolution.
First, how the global architecture of the software, including
code source organization, changes over versions. Second,
how relationships between components evolve. Third, how
metrics evolve with releases. Some representations are
better to visualize an aspect of software but less efficient to
visualize another. We will thus detail all the pros and cons
of each visualization.
5.3.1 Visualizing Organizational Changes
In this section, we present a visualization technique to
depict changes in source code organization (see details in
Section 5.3.1 in Table 1, p. 2).
Holten and Wijk proposed a technique to compare the
software hierarchies of two software versions [49]. It is
inspired by the visualization of source code evolution
presented in Section 5.1. This visualization shows both
versions of the hierarchies and how the hierarchies
are related. To facilitate comparisons, both hierarchies are
organized so that matching nodes are positioned opposite
each other, as much as possible.
To reduce visual clutter, the Edge Bundles technique
presented in Section 4.2 is used. In Fig. 27, the source code
organization of Azureus v2.2 is displayed on the left (2,283
leaves), while v2.3 (3,179 leaves) is on the right. Red
shading is used to depict nodes that are present in one
release but not in the other. With the Edge Bundles
technique, it is easier to precisely select a group of edges
to highlight the selected hierarchy (Fig. 27) or directly select
a node in a hierarchy.
5.3.2 Visualizing Software Metrics Evolution
Static software metrics are abstractions of the source code.
They are a means to better understand, control, manage,
predict, and improve software, as well as its development
and maintenance processes. These metrics can reveal
important characteristics pertaining to the quality of the
product, thus helping develop better software during all the
phases of the software life cycle. Visualizing the evolution of
software metrics gives information about how the software
quality evolves. In this section, we look into several
visualization techniques of metric evolution across software
versions (see details in Section 5.3.2 in Table 1, p. 2).
The Evolution Matrix is a lightweight visualization
technique that displays the entire system evolution in
one picture (Fig. 28) [50], [51]. In their visualization, Lanza
and Ducasse combine software visualization and software
metrics by using two-dimensional boxes and mapping the
number of methods metric to width and the number of
attributes metric to height. Each version of the software
is displayed as a column, and each line represents a
different class.
This visualization technique shows the evolution of the
system size, additions, and removals of classes, growth and
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 927
Fig. 26. Timeline from [48]: Evolution of the “Graphics3D” class of the
Jmol software.
Fig. 27. Comparison of source code organization from [49].
inria-00546158, version 2 - 28 Oct 2011
stagnation phases in the evolution. Several other patterns
can be detected. For instance, classes that grow and shrink
repeatedly during their lifetime can be seen as hotspots in
the system; classes that suddenly grow may be the sign of
unclear design or new bugs; classes that had a certain size
but lost many methods may be removed.
The Evolution Matrix is thus a simple visualization
approach that displays little but useful data. Its creators
consider that one limitation is that the context of the
inheritance hierarchy is lost with the current evolution
matrix visualization. They think that introducing inheri-
tance relationships between classes will increase the
usefulness of this visualization technique.
The VERSO visualization by Langelier et al., presented in
Section 4.3, allows the analysis of software over many
versions [53]. Fig. 29a shows the appearance with VERSO of
a preliminary version of a software. Fig. 29b shows the next
version. A linear interpolation animation is used to go from
one version to the next, the three graphical characteristics
(color, height, and twist) being simultaneously incremen-
ted. The animations last only a second, but attract the visual
attention of the viewer, helping understand program
modifications [188].
During the visualization of the software evolution, small
local changes in the software design can cause relatively
large changes in the Treemap layout [189]. To solve this
problem, the animation of the layout maintains all classes in
the same position during the visualization of all versions, so
that classes are much easier to track. However, this is a
significant waste of space because of classes that have been
deleted in past versions, or have not been created yet in
the current version (Fig. 29). VERSO offers an alternative
animation of the layout to reduce the wasted space in the
early versions when only a few classes are present. It simply
tries to shrink the Treemap of each version in order to use
less space, but with the added constraint that all classes
must keep their relative position.
Visualizing three different metrics, evolving across
versions of the software, can reveal interesting patterns.
Anomalies such as the God Class antipattern or the
Shotgun Surgery can be detected. The former can be
detected as a class, constantly growing in terms of coupling
and complexity. The latter is a class constantly growing in
coupling and whose complexity globally increases but with
an up-and-down local pattern.
The Wettel and Lanza CodeCity visualization tool,
presented in Section 4.3, shows the evolution of a software
by stepping back and forth through the history of the system
while the city updates itself to reflect the currently
displayed version [48]. The age map color mapping (defined
in Section 5.2) is used to depict the age distribution of classes
in the software. Fig. 30 shows the City metaphor at the
method granularity level. Color ranges from light yellow for
the most recent entities to dark blue for the oldest ones.
One drawback of this visualization is that, at a given
time, it is impossible to know when a particular class or
method disappeared, since its representation is an empty
space. Furthermore, it is impossible to single out the
methods whose bodies have been changed from the others.
Finally, the methods of a class are hard to track when
visualizing complete systems. To remedy this, Wettel and
Lanza proposed the Timeline visualization technique,
which focuses on one class or one package but depicts its
entire evolution (Section 5.2).
Pinzger et al. proposed the RelVis visualization technique
that can display the evolution of numerous software metrics
pertaining to modules and relationships [52], [190]. This
visualization technique uses a simple graph and Kiviat
diagrams to graphically depict several metric values by
plotting each value on its corresponding line (Fig. 31). Low
values are placed near the center of the Kiviat, high values
are far from the center. Moreover, the RelVis visualization
technique shows metrics of many versions of the software
by encoding the temporal order of release with a rainbow
color gradient. The different colors indicate the time periods
between two subsequent releases. The width of edges
connecting Kiviat diagrams represents the amount of
coupling between two modules. To keep the graphs
understandable, relationships are drawn in the background
928 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 17, NO. 7, JULY 2011
Fig. 29. Visualization of evolution with VERSO from [53].
Fig. 30. Fine-grained Age Map of JHotDraw from [48].
Fig. 28. Evolution Matrix from [51].
inria-00546158, version 2 - 28 Oct 2011
with a smooth color with low contrast. The RelVis
visualization technique features two representations: one
to visualize a module’s metrics (Fig. 31a), and the other to
visualize metrics on relationships (Fig. 31b).
Fig. 31a displays 3 Kiviat diagrams representing 3
Mozilla modules. Each diagram shows 20 metrics across
seven subsequent releases (numbers from 1 to 7 identify the
versions). This figure is an extract of a larger one from [52].
Metrics that characterize the same property (e.g., size
metrics) are grouped together. Fig. 31a highlights the DOM
module as the largest and most complex module of the
seven releases. Logical couplings increased over all seven
releases. Almost all size metrics increased across versions
showing that the DOM module constantly grew, especially
from release 2 to 3 (cyan). An interesting fact is the number
of global functions that dramatically increased from release
1 to 2 (blue), but decreased in the next release (cyan) and
then remained constant. The number of incoming method
calls increased from release 1 (blue) to the last release 7
(red) with an interesting peak from release 5 to 6 (orange).
The outgoing method calls constantly increased up to
release 6 (orange) but then decreased a lot from release 6 to
7 (red). Apparently, programmers resolved a reasonable
amount of method call coupling.
Fig. 31b presents relationship metrics with half-Kiviat
diagrams. The half-Kiviat diagram that is the closest to a
node corresponds to its incoming metrics. For each relation-
ship between source code entities, RelVis draws a straight
line to indicate the relationship. Fig. 31b shows that
interesting “hot-spots” are, for instance, the relationships
between the module at the bottom right and the module at
the top. We can notice that coupling from the module at the
bottom center to the module at the bottom left decreased
from release 6 to 7 (red). Apparently, release 7 tried to
decouple these two modules.
This visualization contains a vast quantity of information
and can be very useful to identify critical source code
entities or critical couplings. However, this visualization
requires a good knowledge of software metrics even though
some patterns can be easily detected. A good feature of this
visualization technique is the fact that all the information
about metrics and evolution is displayed in one picture
without using animation.
The drawback of this approach is that the colored stripes
sometimes overlap. As a result, the corresponding metric
values cannot be seen. An approach presented in [191] uses
3D Kiviat diagrams to display every version of the software
on a different level of elevation and thus solve the problem
of overlapping.
6CONCLUSION
In this paper, we provide a comprehensive and up-to-date
review of the literature available in the field of visualization
of the static aspects of software and their evolution. The
abundance of conferences, workshops, and symposia in this
research field shows that it is very active and that the
significance of software visualization is growing, both in
academia and industry [192].
In Table 1, p. 2, we summarize the reviewed visualiza-
tion techniques and categorize them according to their
characteristics and features in order to help readers peruse
the paper, be they academics or not.
As indicated in this paper, the software visualization
domain has greatly evolved over the past few years (see
the “Year” column of Table 1, p. 2), giving developers
new tools to analyze, understand and develop software
and helping managers to monitor the overall project to
make effective decisions about its design and refactoring.
However, despite the fact that software visualization tools
have great potential, they are not, as yet, widespread.
Substantial research is still needed to make research
prototypes full-fledged tools. Even so, new commercial
products recently appeared on the market, like SolidFX,
an Integrated Reverse-Engineering environment for C and
C++. This product includes the area of interest visualiza-
tion technique and the Hierarchical Edge Bundles
technique presented in this paper. Particular attention
must be paid to usability issues, and usability evaluation
must be improved.
A trend of this decade is to experiment with new 3D
visualizations. Promising results have been obtained even
though 3D navigation and interactions are problematic.
They can be improved by using new technologies to interact
with and display information (such as large screens, stereo
views, Cave Automatic Virtual Environments, gaze track-
ing, motion tracking).
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 929
Fig. 31. RelVis from [52] (modified). (a) Metrics on modules. (b) Metrics
on relationships.
inria-00546158, version 2 - 28 Oct 2011
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Pierre Caserta received the master’s degree in
computer science in 2008 from the Universite
´
Henri Poincare
´of Nancy in France. He is
currently working toward the PhD degree at the
LORIA Institute, Institut National Polytechnique
de Lorraine, Nancy, France. He teaches at
the Universite
´de Nancy 2, IUT Charlemagne.
His research interests include the visualization
of software, reverse engineering, and immersive
software visualization.
Olivier Zendra received the PhD degree in
computer science with highest honors in 2000
from the the Universite
´Henri Poincare
´of Nancy,
France. He is a tenured researcher at INRIA,
France. His main research interests include the
compilation and optimization of programs, mem-
ory management and automatic garbage collec-
tion, impact of the hardware-software interface
on performance, and power- and energy-saving
optimizations for embedded systems. He was a
key designer of SmartEiffel, The GNU Eiffel Compiler.
.For more information on this or any other computing topic,
please visit our Digital Library at www.computer.org/publications/dlib.
CASERTA AND ZENDRA: VISUALIZATION OF THE STATIC ASPECTS OF SOFTWARE: A SURVEY 933
inria-00546158, version 2 - 28 Oct 2011
... Treemaps allow for the visualization of tree-structured data while supporting mappings to multiple visual variables, including size and color (Johnson and Shneiderman 1991;Carpendale 2003). They are applied for visualization in domains such as business intelligence and software development and facilitate data observation over time (Roberts and Laramee 2018;Caserta and Zendra 2011). Treemaps can be used in static and interactive contexts, i.e., using static images or interactive clients to support interactive visual analytics tasks. ...
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Treemaps depict tree-structured data while maintaining flexibility in mapping data to different visual variables. This work explores how changes in data mapped to color can be represented with rectangular 2.5D treemaps using procedural texture patterns. The patterns are designed to function for both static images and interactive visualizations with animated transitions. During rendering, the procedural texture patterns are superimposed onto the existing color mapping. We present a pattern catalog with seven exemplary patterns having different characteristics in representing the mapped data. This pattern catalog is implemented in a WebGL-based treemap rendering prototype and is evaluated using performance measurements and case studies on two software projects. As a result, this work extends the toolset of visual encodings for 2.5D treemaps by procedural texture patterns to represent changes in color. It serves as a starting point for user-centered evaluation. Graphical abstract
... These characteristics should be considered when specifying map themes or developing visualization techniques for visual information display using software maps. An overview of visualization techniques for static aspects and their evolution, including visualization techniques besides treemaps and software maps, is listed in surveys by Caserta and Zendra (2011) and Merino et al. (2016). ...
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Software maps provide a general-purpose interactive user interface and information display in software analytics. This paper classifies software maps as a containment-based treemap embedded into a 3D attribute space and introduces respective terminology. It provides a comprehensive overview of advanced visual metaphors and techniques, each suitable for interactive visual analytics tasks. The metaphors and techniques are briefly described, located within a visualization pipeline model, and considered within a software map design space. The general expressiveness and applicability of visual variables are detailed and discussed. Consequent applications and use cases w.r.t. different types of software system data and software engineering data are discussed, arguing for versatile use of software maps in visual software analytics.
Chapter
OpenGL is the most widely used API and programming language in college-level computer graphics courses. However, OpenGL programs are difficult to comprehend and debug because they involve programming for both CPU and GPU and the data transfer between them. Modern OpenGL is a complex data flow machine with multiple programmable stages, and it is difficult to trace the partially hidden data flows in the source code written in C++, OpenGL, and OpenGL Shading Language. We have developed a web-based data visualization tool to analyze OpenGL source code and generate interactive data flow diagrams from the source code. The diagrams can help novice programmers build clear mental images of complex data flows. The source code viewer and the data flow diagram are synchronized so that a user can select an OpenGL API call, and the corresponding component in the data flow diagram is highlighted, and vice versa. A programmer can visually step through the data flows and detect specific bugs that are otherwise difficult to find. The main contribution of this paper is an interactive learning tool for computer graphics education.KeywordsSoftware visualizationDebuggingCode comprehensionComputer graphicsComputer science education
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A Software City is an established way to visualize metrics such as the test coverage or complexity. As current layouting algorithms are mainly based on the static code structure, dependencies that are orthogonal to this structure often clutter the visualization and are hard to grasp. This paper applies layered graph drawing to layout a Software City in 3D. The proposed layout takes both the dependencies and the static code structure into account. While having the static dependencies encoded in the layout, we can additionally display dynamic dependencies as arcs atop the city in the night view of the Layered Software City. By applying a trace clustering technique we can further reduce the number of shown arcs. We evaluate the advantages of our layout over a classic layouting algorithm in a controlled study on a real-world project and also report on a short study that evaluates the visualization of dynamic dependencies. The source code of the layouting algorithm and the raw data of the quantitative evaluations are available from https://github.com/qaware/holoware-software-city.
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In recent years, the field of industrial automation is experiencing a dramatic increase of software development and maintenance effort. Driven by shorter product life-cycles and customizable products, production systems are becoming more and more complex, presenting new challenges for control software engineers. In this paper, we report on a visualization concept we applied to industrial automation software. It allows automation software developers to take a look at their software system from a new perspective. Various ways of interacting with the visualization offer further benefits, such as the convenient tracing of control and information flow across multiple hierarchies. We conducted a workshop with five industrial domain experts as a first evaluation of the usefulness of the visualization. Based on their feedback, we discuss open questions and next steps.
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Aspect-oriented software development is a programming paradigm that supports the modularization of crosscutting concerns. The paradigm introduces a new concept, call aspect, along with other concepts and components to capture crosscutting concerns. However, introducing aspects adds difficulties in understanding the structure of program, especially at the maintenance phase. In order to increase understandability of aspect-oriented programs, we propose a visualization approach that uses city transportation system as a metaphor for viewing the structure of aspect-oriented programs. Additionally, we built a prototype tool, called AspectCity, that implements the presented approach. We demonstrated how AspectCity can be used to visualize aspect-oriented programs using two examples. The demonstration shows that the proposed approach can help in understanding aspect-oriented programs. Moreover, the concepts used in AspectCity facilitate ease of communication and do not require effort from the reader to understand the approach due to the use of real life metaphors. AspectCity is a promising approach that can help in solving understandability problem of aspect-oriented programs and decrease their maintenance cost. The approach used in AspectCity can be further extended to be used in visualizing software that contains complex relations between its components.
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SUMMARY Software visualization is concerned with the static visualization as well as the animation of software artifacts, such as source code, executable programs, and the data they manipulate, and their attributes, such as size, complexity, or dependencies. Software visualization techniques are widely used in the areas of software maintenance, reverse engineering, and re-engineering, where typically large amounts of complex data need to be understood and a high degree of interaction between software engineers and automatic analyses is required. This paper reports the results of a survey on the perspectives of 82 researchers in software maintenance, reverse engineering, and re-engineering on software visualization. It describes to which degree the researchers are involved in software visualization themselves, what is visualized and how, whether animation is frequently used, whether the researchers believe animation is useful at all, which automatic graph layouts are used if at all, whether the layout algorithms have deficiencies, and—last but not least—where the medium-term and long-term research in software visualization should be directed. The results of this survey help to ascertain the current role of software visualization in software engineering from the perspective of researchers in these domains and give hints on future research avenues. Copyright c � 2003 John Wiley & Sons, Ltd.
Book
Software Visualization: From Theory to Practice was initially selected as a special volume for "The Annals of Software Engineering (ANSE) Journal", which has been discontinued. This special edited volume, is the first to discuss software visualization in the perspective of software engineering. It is a collection of 14 chapters on software visualization, covering the topics from theory to practical systems. The chapters are divided into four Parts: Visual Formalisms, Human Factors, Architectural Visualization, and Visualization in Practice. They cover a comprehensive range of software visualization topics, including *Visual programming theory and techniques for rapid software prototyping and graph visualization, including distributed programming; *Visual formalisms such as Flowchart, Event Graph, and Process Communication Graph; *Graph-oriented distributed programming; *Program visualization for software understanding, testing/debugging and maintenance; *Object-oriented re-design based on legacy procedural software; *Cognitive models for designing software exploration tools; *Human comprehensibility of visual modeling diagrams in UML; *UML extended with pattern compositions for software reuse; *Visualization of software architecture and Web architecture for better understanding; *Visual programming and program visualization for music synthesizers; *Drawing diagrams nicely using clustering techniques for software engineering.
Conference Paper
Software systems are complex and difficult to analyze. Reengineering is a complex activity that usually involves combining different techniques and tools. MOOSE is an reengineering environment designed to provide the necessary infrastructure for building new tools and for integrating them. MOOSE centers on a language independent meta-model, and offers services like grouping, querying, navigation, and meta-descriptions. Several tools have been built on top of MOOSE dealing with different aspects of reengineering like: visualization, evolution analysis, semantic analysis, concept analysis or dynamic analysis.