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Automatic Generation of Configuration Files: an Experience Report from the Railway Domain.

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Journal of Object Technology | RESEARCH ARTICLE
Automatic Generation of Configuration Files: an
Experience Report from the Railway Domain
Enxhi Ferko, Alessio Bucaioni, Jan Carlson, and Zulqarnain Haider
Mälardalen University, Sweden
Bomdardier Railway Transportation, Sweden
ABSTRACT
In recent years, software product line development has been adopted by a growing number of companies. Within
software product line development, one way of creating specific products is by using configuration files to control a given set
of parameters of the product at run time. Often, configuration files are created manually and this may lead to a sub-optimal
process with respect to development effort and error proneness. In this experience report, we describe our work in enabling the
automatic generation of configuration files in the railway domain. We discuss a four-step approach whose generation mechanism
uses concepts of generative programming. The approach is the outcome of a bottom-up effort leveraging the experiences
and the results from our technology transfer activities with our industrial partner, Bombardier Transportation. We evaluate
the applicability and the correctness of the proposed approach using the Aventra train family from Bombardier Transportation.
Besides, we evaluate the ability of the proposed approach in mitigating the development effort and error proneness typical of
traditional manual approaches. We performed expert interviews to assess the industrial relevance of the proposed approach
and collect qualitative feedback on the perceived benefits and drawbacks. Eventually, for each of the four steps composing the
proposed approach, we identify factors that might affect the adoption of the approach and use these factors for discussing the
lessons we have learned.
KEYWORDS Software Product Line, Configuration File, Automatic generation.
1. Introduction
In recent years, many companies have witnessed an increasing
demand for customised software-intensive systems able to ad-
dress different market needs, regional standards, certifications
as well as software and hardware requirements. Bombardier
Transportation (BT) is one such company.
1
To meet this increas-
ing demand for customisation, BT has been shifting its product
development towards Software Product Line (SPL) (Klaus Pohl
2005). SPL is a software development paradigm where a single
system is developed to meet the needs of a product family, hence
several products with commonality and variability (Metzger &
JOT reference format:
Enxhi Ferko, Alessio Bucaioni, Jan Carlson, and Zulqarnain Haider.
Automatic Generation of Configuration Files: an Experience Report from
the Railway Domain. Journal of Object Technology. Vol. 20, No. 3, 2021.
Licensed under Attribution 4.0 International (CC BY 4.0)
http://dx.doi.org/10.5381/jot.2021.20.3.a4
1https://www.bombardier.com/en/transportation.html
Pohl 2014). In a nutshell, SPL focuses on identifying and mod-
elling similarities and differences of a product family and using
this information for deriving and configuring specific products
of the family. SPL differentiates between two processes, namely
domain engineering and application engineering (Klaus Pohl
2005). Domain engineering focuses on defining the commonal-
ity and variability of the product family, as well as developing
the common and distinguishing software assets. Application
engineering uses these assets to derive specific products of the
family by selecting variability options for matching product
requirements and functionalities. SPL provides the opportunity
of decreasing the overall development cost while providing for
higher quality and shorter development time compared to the
development of multiple independent systems.
In BT, the adoption of SPL has brought some challenges and
difficulties, too (Metzger & Pohl 2014). One of the main open
challenges that BT is facing is how to derive specific products
from a family. Once a product has been designed, there are
An AITO publication
Figure 1 Mapping proposed steps to the SPL process
several ways in which the design can be turned into a concrete
product. One common option, which is used by BT and is
the focus of this work, is to realise individual products using
configuration files. A configuration file is part of the concrete
realisation of the system and determines, at run time, some of its
aspects. A typical example of a configuration file would be an
XML data file with parameters that enable or disable different
portions of the common source code according to the features
selected for that particular product. In BT, configuration files
are currently created manually starting from a set of heteroge-
neous documents. These documents often provide for a general
and informal description of the products and their features, only.
Besides, they might not be stored and managed systematically.
Starting from these documents, BT engineers manually create
configuration files for the different products in the family. Expe-
riences from BT show that manually creating configuration files
starting from a set of heterogeneous and informal documents
is time-consuming and error-prone. The most common errors
reported by engineers are categorised as (i) omitting informa-
tion, (ii) wrong semantics, and (iii) inconsistencies. Besides,
this manual process does not allow exploiting product common-
alities, meaning that common information needs to be specified
for each product.
In this experience report, we describe our experience in au-
tomating the generation of SPL configuration files in the rail-
way domain within BT. We enable the automatic generation
of configuration files defining a four-steps approach whose
generation mechanism leverages concepts of generative pro-
gramming (Czarnecki & Eisenecker 2000). We demonstrate the
applicability and correctness of the proposed approach using an
industrial SPL from BT being the Aventra train SPL. Besides,
we evaluate the ability of the proposed approach in mitigating
the development effort and error proneness typical of traditional
manual approaches. The application on the Aventra SPL sug-
gest that the proposed approach has helped BT in lowering the
development effort and mitigating the error proneness typical of
the traditional, manual approaches already for SPL containing
more than 3 products. Eventually, we use experts interviews to
the Aventra Development team for assessing the industrial rele-
vance of the proposed approach and for collecting qualitative
feedback on the perceived benefits and drawbacks. For each
step of the proposed approach, we identify a number of factors
and alternatives to take into account for adapting the approach
to other development process and domain. Eventually, we use
these factors and alternatives for discussing the lessons we have
learned.
The remainder of this paper is structured as follows. In Sec-
tion 2, we present the proposed approach, its steps, and the
generation mechanism. In Section 3, we show the application
of the proposed approach on the Aventra SPL. In Section 4
and Section 5, we evaluate the proposed approach and discuss
lessons learnt and generalisability, respectively. In Section 6,
we present some related researches documented in literature.
In Section 7, we conclude the paper with final remarks and
possible future work.
2. Proposed Approach
In this section, we describe the proposed approach for automati-
cally generating configuration files within the BT development
process. Figure 1 provides a graphical representation of the
approach in relation to a simplified version of the SPLE frame-
work presented by Pohl et al. (Klaus Pohl 2005). the two main
phases of a typical SPLE process are Domain Engineering and
Application Engineering, which are represented as white rect-
angles in Figure 1. Each main phase consists of a number of
sub-phases represented as red rectangles.
The proposed approach consists of four steps being Feature
Categorisation,Creation of the Variability Model,Variant Con-
straints Categorisation and Generation of Configuration Files.
Figure 1 represents these steps as circled numbers and places
them in relation to the sub-phase they occur in. In the remainder
of this section, we describe each step of the proposed approach.
2.1. Feature Categorisation
Feature Categorisation is the first step of the proposed approach
and should be performed during the Domain Analysis sub-phase.
Domain Analysis is responsible for defining, documenting, and
validating all the shared and individual requirements of the SPL.
These requirements are further mapped to features, which are
used for defining the variability model of the SPL during the
Domain Design sub-phase. An example of this could be the
requirement that a train has two driver cabins, which would
translate in the feature direction indicating the orientation of
2 Ferko et al.
the train. Industrial SPLs often consist of thousands of features,
which are typically neither organised nor prioritised. Managing
such a huge number of unorganised features is a complex task,
which negatively affects the product derivation process (Loesch
& Ploedereder 2007). The categorisation of the features identi-
fied in the Domain Analysis sub-phase is of crucial importance
for BT.
Feature Categorisation focuses on grouping the elicited fea-
tures into Primary Features and Secondary Features. Primary
features are all those features whose combinations can uniquely
identify products in the SPL. Within BT, voltage,number of
cars, and side of consist are primary features as the combination
of their values can uniquely identify a certain train. Secondary
features are all those features, which do not explicitly define
a product. Max speed is an example of a secondary feature in
the case of BT. The output of the Feature Categorisation step
is a list of features labelled as primary or secondary. Based on
the complexity of the SPL and the result of the categorisation,
secondary features can be included or excluded from the feature
model of the SPL. In the first case, the secondary features will
be automatically added to the configuration files. This strat-
egy leads to a complete, but potentially unmanageable feature
model. In the second case, the secondary features need to be
added manually to the configuration files. Such a strategy leads
to an incomplete, but light-weight feature model. In Section 5,
we discuss the advantages and drawbacks of each strategy and
discuss the lessons we have learned in our work with BT.
2.2. Creation of the Variability Model
Creation of the Variability Model is the second step of the
proposed approach and should be performed during both the
Domain Design and Domain Realisation sub-phases. Domain
Design and Domain Realisation are responsible for defining
the variability model and implement the related domain arte-
facts. The variability model represents the commonalities and
differences of the SPL products. The variability model con-
sists of variation points, variants, and their relationships and
constraints. A variation point is a representation of a loca-
tion, where a feature can have different values.
2
For instance,
voltage is a variation point with values being Dual Voltage
(DV),Direct Current (DC) and Alternating Current (AC). A
variant is a realisation of a variation point. Creation of the
Variability Model focuses on the creation of a model capturing
this information and the output of this step is a formalisation
of the variability model. Currently, there is no standard way
of representing variability models (Arboleda & Royer 2012)
and different companies may use different notations and tools.
One of the most used notations for representing the variabil-
ity model is feature model (Danilo Beuche 2006). Feature
modelling is a well-defined formalism, which is currently sup-
ported by several open-source and commercial tools, such as
FeatureIDE (Meinicke et al. 2017). Another possibility for rep-
resenting variability models is using metamodelling for building
a domain-specific language (DSL) describing the SPL variation
points and variants. Most of the commercial tools supporting
2
In the remainder of this paper, we use the terms feature and variation points
analogously.
feature modelling are built around ad-hoc DSLs. In Section 5,
we discuss some aspects to consider when choosing one ap-
proach over the other that have emerged as pivotal during our
work with BT.
2.3. Variant Constraints Categorisation
Variant Constraints Categorisation is the third step of the pro-
posed approach and should be performed during the Product
Analysis and Product Design sub-phases. These sub-phases are
focused on configuring all the products within the SPL. This
involves the selection of a valid and complete set of variants
together with possible constraints on them. We have observed
that in BT, variant constraints and their management have a di-
rect impact on the complexity of the generation of configuration
files and the complexity of the product realisation. To ease the
management of variant constraints, we propose to categorise
them into Technical Constraints and Customer-specific Con-
straints. Technical constraints are all those constraints, which
prevent the engineer to select erroneous or invalid variants. An
example of this could be a constraint preventing the selection
of pantograph and diesel engine variants for trains not having
the electrical engine variant. Customer-specific constraints are
all those constraints, which bind the choice of variants based on
customer preferences. An example of this can be the orientation
of a car (same or different from the leading car), which can dif-
fer from a customer to another. Technical and customer-specific
constraints can refer indiscriminately to primary and secondary
features. While most of the time technical constraints would
be specified on primary features, there might be cases when
technical constraints would be specified on a secondary feature,
too, so to avoid erroneous configuration of a product. Similarly,
customer-specific constraints can be specified on primary fea-
tures. The output of this step is the categorisation of variant
constraints into technical and customer-specific. Based on the
total number of constraints, customer-specific constraints can be
specified or omitted. In the case they are omitted, the customer-
specific constraints need to be added directly during the configu-
ration file generation. This solution yields towards a lighter and
more malleable SPL with respect to addition, modification and
deletion of products, variation points and variants. However,
such a solution might reduce the degree of automation. Specify-
ing both technical and customer-specific constraints yields to
a less malleable solution with respect to the above-mentioned
cases, but it enables full-fledged automation. In Section 5, we
discuss the advantages and drawbacks of both solutions when
applied in the Aventra SPL.
2.4. Generation of Configuration Files
Generation of Configuration File is the last step of the proposed
approach and should be performed during the Product Realisa-
tion sub-phase. In this phase, products are configured based on
the identified variants and variant constraints. For each derived
product, technical values of the variants are expressed in the
configuration files, which are part of the concrete realisation of
the software and determines at run-time the set-up of the actual
software. Hence this step focuses on the automatic generation
of such configuration files.
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 3
Collector
Features and
constraints
List of variations
points and variants
Executor
Translation
file
Configuration
file
Figure 2
Mechanism for the automatic generation of configu-
ration files
There might be several alternatives in how to achieve such
an automatic generation. One option is by using transformation
languages and model transformations (Sendall & Kozaczynski
2003). Model transformations are automated processes that take
one or more source models as input and produce one or more
target models as output, according to a set of transformation
rules. An example of this could be the use of the template-
based language Acceleo (Nesrine & Bennouar 2018) for the
automatic generation of configuration files starting from models
representing the SPL. These models should be conforming to
metamodels. This solution benefits from the tooling, which
usually accompanies such transformation languages. One draw-
back is that model-based solutions usually entail the knowledge
of concepts as modelling, metamodelling, and model transfor-
mation. We have noticed that this knowledge is rarely possessed
and mastered by the engineers at BT, which are also unfamil-
iar with model-based tooling (Liebel et al. 2014). Another
drawback of this solution is the certification process. Being a
safety-critical domain, the railway domain needs to comply with
several safety standards, e.g., IEC 61508 (Bell 2006). In par-
ticular, the European standard EN 50128 specifies the process
and technical requirements for the development of software for
programmable electronic systems for use in railway control and
protection applications (CENELEC 2020). EN 50128 defines
three classes of tools of ascending criticality, which are T1, T2,
and T3 (CENELEC 2020). According to this categorisation,
modelling and transformation languages and environments fall
in the T3 category as they could introduce errors in the final
executable. Among other requirements, tools in the T3 category
need (i) to demonstrate a suitable history of successful tool
use in a similar environment, (ii) have diverse redundant code,
which allows the detection and control of failures, (iii) comply
with the safety integrity levels, and (iv) demonstrate a record of
validation activities (CENELEC 2020). Such requirements are
assessed by external certification bodies in a process, which may
take up to several years and add a development cost overhead
between 25 and 100% (Pop et al. 2016).
Another possibility to achieve the automatic generation of
configuration files is by using traditional programming lan-
guages for realising concepts of generative programming (Czar-
necki & Eisenecker 2000). In a nutshell, generative program-
ming refers to programs that are written for creating software
components in an automated fashion. Generative programming
is considered the ancestor of metamodelling and model trans-
formation. This solution may allow mitigating the certification
cost in the case it can be realised using programming languages
and tools already used within the company, hence already cer-
tified. In Section 5, we discuss the advantages and drawbacks
of both alternatives. In this research effort, we have developed
one such mechanism for the automatic generation of configu-
ration files using C# and leveraging the concepts of generative
programming.
2.4.1. Mechanism for the Automatic Generation of Con-
figuration Files
Figure 2 shows a simplified representation
of the functional architecture of the mechanism for the auto-
matic generation of configuration files. It consists of two main
modules, namely Collector and Executor (represented as red
rectangles in Figure 2) and one Translation File (represented as
a red note in Figure 2). The Executor module is implemented in
C# while the Collector module represents any feature modelling
environment. The mechanism takes the following as input: the
list of features and constraints, and a translation file. In the
first step, the Collector module is used for gathering the list
of features and their values. Besides, it considers the speci-
fied technical and customer-specific constraints for establishing
relationships among the selected features. These constraints
might be expressed in formal or informal notation. For each
product, the Collector resolves these constraints and produces
an XML data file where each feature is marked as automatically
selected, automatically deselected, or manually selected to spec-
ify all features selected for one final product. In particular, a
feature can be automatically selected or deselected based on
the resolution of a technical constraint. A feature can be manu-
ally selected as a result of the resolution of a customer-specific
constraint. Listing 1 shows an excerpt of one of such files in
which the maxSpeed feature is selected automatically and the
caro feature is selected manually. If using a feature modelling
environment, these steps correspond to the modelling of the
SPL. In the second step, the Executor translates the information
about selected features into a configuration file, according to the
relations specified in the Translation File. In a nutshell, these
relations link selected features to corresponding objects in the
configuration files. An example of these relations are:
Parameter-to-Features each parameter in the configuration
file is associated to the list of features that might contribute
to its specification. For instance, in Listing 2 parameter1
is associated to variant1 and variant2, to variant1 or to
variant1 and variant3
Features-to-ParameterValue the value of the parameter is
selected considering the list of features actually contribut-
ing to that parameter.
Listing 2 shows an excerpt of the general structure of the trans-
lation file developed for this research effort using the JavaScript
Object Notation (JSON). In Section 3, we show the concrete
Translation File developed for the Aventra SPL.
4 Ferko et al.
1<configuration>
2...
3<feature automatic="selected" name="maxSpeed"/>
4<feature manual="selected" name="caro"/>
5...
6</configuration>
Listing 1 Example of list of active feature for a product
1{"parameterName1": {
2"Type": "Type of parameter1",
3"Comment": "Comment for parameter1",
4"Values": [
5{"Features": [ "variant1", "variant2" ],
6"Value": "technicalValue1"},
7{"Features": [ "variant1" ],
8"Value": "technicalValue2"},
9{"Features": [ "variant1", "variant3" ],
10 "Value": "technicalValue3"}]
11 },
12 "parameterName2": {...},
13 ....,
14 "DefaultValue": −1
15 }
Listing 2 Example of the translation file
The Executor uses the relations in the Translation File for au-
tomatically creating configuration files, and it is realised as
a console application. It takes as inputs the path to the folder
where the files from FeatureIDE are stored, the path to the folder
where the generated configuration files will be stored, and the
path to the translation file. First, the Executor collects the infor-
mation expressed in the JSON file and stores it in a data structure
called Translation Collection. The Translation Collection has
the information expressed in the JSON file such as the parame-
ters to be generated, their possible mapping options to features,
and respective technical values. Then, starting from the list of
variants and variation points, the Executor extracts the features
marked as selected (either manually or automatically) and stores
this information in a data structure called Feature Collection.
Eventually, for each parameter in the Translation Collection, the
Executor checks which combination of features are selected in
the Feature Collection and assigns the corresponding technical
value. This is done for all the products. For instance, using the
relations in Listing 2, the Executor will derive parameter1 from
the features variant1 and variant2 with value technicalValue1 if
the features variant1 and variant2 are selected. Alternatively, it
derives it from the feature variant1 with value technicalValue2
if only feature variant1 is selected. Or, it can derive it from
the features variant1 and variant3 with value technicalValue3 if
the features variant1 and variant3 are selected. A default value
is added in case none of the options is triggered. Engineers
can filter all configuration files with parameters that have a de-
fault value to find any possible inaccuracy when configuring
the products. The result of this step is a configuration file for
each product in the SPL. In Section 3, we provide an example
of configuration files.
3. Applying the Proposed Approach to the
Aventra SPL
In this section, we demonstrate the industrial applicability of
the proposed approach using the Aventra SPL from Bombardier
Transportation. The Aventra SPL is a family of passenger trains
designed by Bombardier for the British market. The trains in the
Aventra SPL might be of three types: the London Overground
train (LOT), the East Anglia train (EAA), and the South West-
ern Rail train (SWR). Each train might have a specific number
(e.g., four, five, ten) and type (e.g., passengers carrying cabin,
drivers cabin) of cars, power supply (e.g., Dual Voltage(DV),
Alternative Current (AC), Direct Current (DC)) and other char-
acteristics. In addition to differences at the train level, there
might be differences at car level, too. An example of this could
be the orientation (same or opposite direction as the leading
car) or the position of the car. All the train functions such as,
on-board communication, passenger information, entertainment,
are controlled by the Train Control and Management System
(TCMS), which is a complex system consisting of different soft-
ware and hardware units connected via different communication
links, such as Internet Protocol (IP) networks. Most of the func-
tionalities of TCMS units are common for different types of
trains. Some of the generic functions in TCMS units are:
Doors control function — controlling the opening and
closing of train doors.
Passenger information function — displaying real-time
information to the passenger
Pantograph up/down function — indicating if the panto-
graph is in contact with the electric lines.
In addition, each of these units might have few modules de-
veloped differently for each train to accommodate the train
differences. In total, the Aventra SPL composes of 12 different
trains, 17 variation points, and 63 variants.
3.1. Aventra SPL Feature Categorisation
According to the proposed methodology, the first step to be per-
formed is the elicitation and categorisation of the SPL features.
We have elicited the Aventra SPL features from the Software
Architecture and Design Specification (SAS) of Aventra TCMS
Applications using the third degree of data collection technique
introduced by Lethbridge et al. (Lethbridge et al. 2005). This
activity has identified 63 variants grouped in 17 variation points.
In sum, 12 final products are configured starting from the 4 pri-
mary features and related constraints. Table 1 shows the elicited
features together with their values.
We have decided to include the secondary features with cor-
responding options in the variability model for a number of
reasons, including the following. In the Aventra SPL, we had
a small number of secondary features. Hence, including them
in the variability model, did not lead to an unmanageable vari-
ability model. Omitting secondary features from the variability
model would have hampered the automatic generation of config-
uration files and required a considerable amount of additional
work for manually specifying these features in each and every
configuration file. In addition, having secondary features in the
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 5
Feature
name
Categorisation Description
type Primary
Type of train. It can be t_LOT, t_EAA,
t_SWR
carNr Primary
Number of car per consist. It can be 4,
5 or 10.
voltage Primary
High voltage configuration in the con-
sist. It can be AC, DC, DV.
maxSpeed Secondary
It can be unknown, 140kph/87mph,
180kph/111mph or 250kph/155mph.
doorsPerCar
Secondary
Number of doors per car. It can be 1, 2,
3, 4 or 5.
sideOfConsist
Primary Side of the consist. It can right or left.
cartype Secondary
Type of car in the consist. It can be A,
B, C, D, E.
carOrient Secondary
Orientation of the car with respect the
leading car. It can be unknown, same or
opposite.
Table 1 Features for the Aventra SPL
variability model gave us the possibility of specifying variants
constraints on such features.
3.2. Aventra SPL Variability Model
In the second step of the proposed approach, the elicited fea-
tures and their values are used to create a model of the SPL
variability model. We have created the model of the SPL using
the FeatureIDE tool, which is an Eclipse-based framework for
feature-oriented software development. FeatureIDE provides
for a user-friendly visualisation of the features and their rela-
tionships in the model. It supports multi-views configuration of
each product. It provides support for the evolution of the feature
model simply enabling the addition or deletion of features in
the feature model. In addition, FeatureIDE provides variant
constraints management and constraints can be added, deleted,
or modified in accordance with user needs. Figure 3 to Fig-
ure 5 show the FeatureIDE model of the Aventra SPL variability
model. For the sake of readability, we have split the model
into three figures: Figure 3 shows the primary features together
with their possible values while Figure 4 and Figure 5 show the
secondary features and their possible values. It is worth noting
that the categorisation of features in primary and secondary in
the feature model is only logical hence has no direct impact on
the variability model or configuration files. FeatureIDE allows
to mark features as mandatory,optional,concrete and abstract.
Mandatory features are those features that hold for all the prod-
ucts in the SPL. For instance, all the trains will have the type
feature, but only ten-cars-per-consist trains will have the side-
OfConsist feature. Optional features are features that might be
omitted for given products. Concrete features are features that
will be included in the configuration file. We have used concrete
features for representing variants. Abstract features represent
features that will not be included in the configuration file. We
have used abstract features for representing variation points. In
addition, features can be assigned in the so-called alternative
group. Features in an alternate group are mutually exclusive.
In the variability model in Figure 3 to Figure 5, we have used
alternative group features for representing variants of a variation
point. When features are marked within an alternative group,
FeatureIDE generates implicit constraints to ensure the correct
semantic.
3.3. Avetra SPL Variant Constraints
In FeatureIDE, variant constraints (also known as cross-tree
constraints (Seidl et al. 2016)) are expressed using Boolean-
like formulas via the create constraint functionality. Variant
constraints can be updated and new variant constraints can be
added at any point in time. In the Aventra SPL, we have decided
to add only technical constraints to the variability model. The
main reason for such a decision was to ensure the separation
of concerns between domain knowledge, expressed by techni-
cal constraints, and customer preferences. The Aventra SPL
technical constraints were:
1. tLOT carNr4carNr5
2. tLOT carNr5vDV
3. tLOT carNr4→ ¬vD C
4. tEAA vAC
5. tSWR carNr5car Nr10
6. tSWR → ¬ vAC
7. carNr10 sid eO f Consi st
8. carNr4carNr5→ ¬s ideO f Con sist
9. carNr5carNr10 car5ty pe
10. carNr5carNr10 car5o
11. carNr4→ ¬car5ty pe
12. carNr4→ ¬car5o
Technical constraints impose restrictions on variants of different
variation points. The first constraint specifies that a train of type
LOT can only have four-cars or five-cars consists. The second
constraint specifies that a train of type LOT having five-cars con-
sists will have a dual voltage system. The third imposes direct
current systems for trains of type LOT. The fourth constraint
states that all trains of type EAA must have an alternating cur-
rent system. The fifth and sixth constraints specify that trains of
type SWR must have five-cars or ten-cars consists and that can
not have an alternating current system. The seventh constraint
specifies that the feature sideOfConsist can be specified only
for ten-cars consists. In fact, a ten-car consist is composed of a
permanent linking of two five-car sets hence the two sides of con-
sists might have different configurations of cars and functions.
The eighth constraint specifies that the feature sideOfConsist
can not be specified for four-cars or five-cars consists. Ninth and
tenth constraints specify that features car5type and car5o can
be specified only for trains having five-cars or ten-cars consists,
while constraints number eleven and twelve states that car5type
and car5o features can not be specified for trains having four-
cars consists. FeatureIDE provides a graphical editor for the
6 Ferko et al.
Figure 3 Primary Features of the Aventra SPL variability model.
Figure 4 Secondary Features of the Aventra SPL variability model (I).
Figure 5 Secondary Features of the Aventra SPL variability model (II).
visualisation of products and their features. For each product,
features are organised in a tree structure where leaves represent
possible values of features as shown in Figure 6 and Figure 7.
Each feature and feature value are provided with a checkbox,
which can be used for selecting or deselecting that feature or
value (selected features are marked with a green plus in Figure 6
and Figure 7). FeatureIDE prevents users from selecting invalid
combinations of features or values meaning combinations that
violate the specified constraints. All the features and the values
specified as mandatory in the constraints are automatically se-
lected. Similarly, features and values excluded by the specified
constraints are automatically disabled and cannot be selected.
For instance, Figure 6 shows that the value v_DC is deselected
because of a technical constraint and that value v_DV is manu-
ally selected, instead. Similarly, Figure 7 shows that the feature
car5type is automatically deselected because of the specified
constraint.
3.4. Generating Aventra SPL Configuration Files
The generation of the Aventra SPL configuration files is en-
trusted to the automation mechanism described in Section 2.
FeatureIDE provides a mechanism for creating XML data files
containing the list of features along with their values. These files
are created starting from the three structures described above
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 7
Figure 6
Tree constraint in configuration editor for
LOT4carDV
Figure 7
Cross-tree constraint in configuration editor for
LOT4carDV
and for each product of the SPL. In the context of the mech-
anism presented in Section 2 these files are equivalent to the
list of variation points and variants created from the Collector
module. We have used such a feature for creating the files con-
taining the list of features that are selected for one product and
their values of the Aventra SPL. Listing 3 describes a fragment
of the file containing the list of variation points and variants for
the LOT4carDV product.
1<configuration>
2...
3<feature automatic="selected" name="type"/>
4<feature manual="selected" name="t_LOT"/>
5<feature automatic="unselected" name="t_EAA"/>
6<feature automatic="unselected" name="t_SWR"/>
7<feature automatic="selected" name="carNr"/>
8<feature manual="selected" name="carNr_4"/>
9<feature automatic="unselected" name="carNr_5"/>
10<feature automatic="unselected" name="carNr_10"/>
11<feature automatic="selected" name="voltage"/>
12<feature automatic="unselected" name="v_AC"/>
13<feature automatic="unselected" name="v_DC"/>
14<feature manual="selected" name="v_DV"/>
15<feature automatic="selected" name="maxSpeed"/>
16<feature manual="selected" name="sp_140kph87mph"/>
17<feature automatic="unselected" name="sp_180kph111mph"/>
18<feature automatic="unselected" name="sp_250kph155mph"/>
19<feature automatic="selected" name="DoorsPerCar"/>
20<feature automatic="unselected" name="D_one"/>
21<feature manual="selected" name="D_two"/>
22<feature automatic="unselected" name="D_three"/>
23<feature automatic="unselected" name="D_four"/>
24<feature automatic="unselected" name="D_five"/>
25...
26</configuration>
Listing 3
List of variation points and variants for the
LOT4carDV product.
This product is a LOT train characterised by four cars and a dual
voltage system. Its max speed is 140 kilometres per hour and
it has two doors per car. Accordingly, the variation points and
variants corresponding to these values are marked as selected.
For the sake of space, we only show a portion of the file contain-
ing the list of variation points and variants for the LOT4carDV
product. The interested reader can find the other files here.
3
It should be noted that the higher the number of constraints in
the SPL model, the higher is the number of features that can be
automatically selected or deselected. However, the complexity
of specifying new constraints increases with the total number
of constraints as each of these is specified through Boolean
expression (which needs to take into account already specified
ones). All these files are provided as input to the generation
mechanism together with the translation file described in Sec-
tion 2. In Listing 4, we report an excerpt of the translation file
developed for the Aventra SPL. In particular, Listing 4 shows
the relations responsible for the translation of S_B_Project and
ST_B_MaxSpdHmi parameters. For the sake of space, we only
report portions of these files. Listing 5 shows the generated
configuration file for the LOT4carDV product. In particular, we
can see that the features have been translated into parameters
according to the relations specified in the translation file in List-
ing 4. For instance, the combination of features type and carNr
has been translated into the S_B_Project parameter and their
values t_LOT and carNr_4 into the parameter value 1(lines 1
to9ofListing 4).
3https://zenodo.org/record/4737049#.YJFBwy0Rrxh
8 Ferko et al.
1{"S_B_Project": {
2"Type": "Integer",
3"Comment": "Customer project: 1: Lotrain 4 cars, 2: Lotrain 5 cars, 3: East
Anglia 5 cars, 4: East Anglia 10 cars (side A or B of 5 car consist), 5:
intentionally empty, 6: South West 5 cars, 7: South West 10 cars (side A
or B of 5 car consist)...",
4"Values": [
5{ "Features": [ "t_LOT", "carNr_4" ],
6"Value": 1},
7{"Features": [ "t_LOT", "carNr_5" ],
8"Value": 2},
9...]},
10 "ST_B_MaxSpdHmi": {
11 "Type": "Integer",
12 "Comment": "Max speed dial value;Value interpretation: 0−unknown, 1−
140kph/87mph, 2−180kph/111mph, 3−250kph/155mph,,",
13 "Values": [
14 {"Features": [ "sp_140kph87mph" ],
15 "Value": 1},
16 {"Features": [ "sp_180kph111mph" ],
17 "Value": 2},
18 {"Features": [ "sp_250kph155mph" ],
19 "Value": 3},
20 ]},...,
21 "DefaultValue": −1
22 }
Listing 4 Example of the translation file for the Aventra SPL
1<ParameterSet>
2...
3<Parameters>
4<Parameter Name="S_B_Project" Type="Integer" Value="1" />
5<Parameter Name="ST_B_MaxSpdHmi" Type="Integer" Value="1" />
6<Parameter Name="HV_config" Type="Integer" Value="1" />
7<Parameter Name="Nr_of_cars_in_consist" Type="Integer" Value="4" />
8<Parameter Name="Nr_of_doors_per_car" Type="Integer" Value="2"/>
9<Parameter Name="Type_car1" Type="String" Value="D" />
10 <Parameter Name="Orientation_car1" Type="Integer" Value="2" />
11 ...
12 </Parameters>
13 </ParameterSet>
Listing 5
Generated configuration file for the LOT4carDV
product.
4. Evaluation
In this experience report, we describe our experience in au-
tomating the generation of SPL configuration files in the railway
domain with BT.
In this section, we evaluate the correctness of the pro-
posed approach together with its ability in lowering the error-
proneness and the developing effort typical of the manual ap-
proach. We use expert interviews for assessing the industrial
relevance of the proposed approach and collecting qualitative
feedback on its benefits and drawbacks. Eventually, we dis-
cuss the main threats to validity for this research and related
mitigation strategies.
When defining the automation mechanism, we have created
both the Executor and the Translation file so that they would
generate configuration files identical to the handcrafted ones
that were previously used within BT. It is important to note that
having identical configuration files was of crucial importance
for BT. In fact, differences in the configuration files would
affect the software running in the trains, which would need to
be updated. Assuming that the correct set of variation points
and variants are selected, there is only one factor that could
undermine the generation of identical configuration files, which
is the presence of errors in the Translation file. In order to show
that the Translation file is free from errors, we have compared
the 12 generated configuration files for the Aventra SPL with
the handcrafted ones using a visual difference tool focusing on
files, directories, and version controlled projects comparison.
The results of the comparison have shown that all the generated
configuration files were 100% identical to the manually created
ones. The interested reader can access the comparison here.
4
Hence, the proposed mechanism is correct. One may argue that,
in general, there is still the possibility to introduce errors when
writing the mappings in the Translation file. While this is a valid
concern, such a risk can not be completely removed although
we have identified several mitigation strategies that could be
added to our automation mechanism (we discuss this in the
following section). Moreover, it should be noted that this risk is
more likely to happen in a traditional manual approach as the
engineer would need to rely on the mappings that we formalise
in the translation file each time she writes the configuration file
for a product in the SPL (while in the proposed process the
Translation file is written only once per SPL).
One of the main goals of the proposed approach is to miti-
gate the error proneness typical of manual approaches. When
working on the Aventra SPL, engineers in BT have identified
three main categories of errors that can be made when manually
creating the configuration files, being (i) omitting information:
parameters or technical values are omitted from configuration
files, (ii) wrong semantics: the parameters and their value are
inserted in the document, but they are interpreted wrongly, (iii)
inconsistencies: parameters or technical values are inconsistent
among the configuration files. Errors in the first and third cate-
gories are implicitly avoided using the proposed approach. In
fact, both parameters and values are automatically generated
starting from the same SPL model and Translation file. This
means that it is not possible to have two or more configuration
files having, for instance, a different set of parameters. Besides,
all the parameters and their value are generated taking into ac-
count the set of identified variation points and variants. Hence,
no information is omitted or lost in the process of generating
configuration files. The above mentioned comparison among
generated and manually created configuration files shows that
the proposed mechanism is free from inconsistencies and in-
formation loss. Within the proposed approach, errors in the
second category may arise if an erroneous Translation file is
created. However, compared to the traditional manual approach,
the proposed mechanism drastically reduces the possibility of
such errors. In fact, the Translation file is only written once per
4https://zenodo.org/record/4737049#.YJFAXC0Rrxg
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 9
SPL as opposite to the manual approach where such errors can
happen each time an engineer writes a configuration file for a
product in the SPL.
Another important goal of the proposed approach is to lower
the development effort of the configuration files. In order to
evaluate this aspect, we have compared the number of artefacts
that need to be manually created with the proposed approach
and with the traditional one. If
n
is the number of products
in a SPL, then the number
N
of manually created or modified
artefacts for the proposed approach is
Nproposeda pproach =3
.
Within the proposed approach, an engineer needs to manually
create the Collector, Executor, and Translation file. If
n
is the
number of products in a SPL, then the number
N
of manually
created or modified artefacts for the traditional manual approach
is
Nmanuala p proach =n
. With manual approaches, the engineers
would need to manually create a configuration file for each of
the
n
products in the SPL. By estimating the number of manu-
ally created artefacts with both approaches, it is evident that the
proposed mechanism is able to reduce the development effort
for the configuration files. This suggests that the proposed ap-
proach discloses the opportunity of lowering development effort
already for SPLs containing three products. In this comparison,
we assume that the effort of eliciting and managing features
is the same with both approaches and that the SPL is newly
created. If that is not the case, then the number
N
of manu-
ally created or modified artefacts for the proposed approach
is
Nproposeda pproach =4
. In fact, an engineer would need to
manually create the SPL model besides the already mentioned
artefacts. It is worth mentioning that the complexity of the SPL
model is directly related to the number
n
of products in the SPL.
However, we can reasonably state that for reasonable
n
-values,
the development effort related to manual models in traditional
approaches is greater than the effort related to the creation of
the SPL model, Collector, Executor, and Translation file in the
proposed approach.
In order to discuss the development effort needed in the
case of evolving SPLs, we have identified three different sce-
narios. The first scenario involves adding new functionality
for any existing product in a SPL as the result of a customer
need. In the context of the Aventra SPL, this could be the in-
stallation of a new air conditioning system for the EAA trains.
This scenario requires updating all the configuration files of all
the products in the SPL so to reflect the new parameter along
with its technical value. If
n
is the number of products in the
SPL, manual approaches would require
n
modifications while
the proposed approach would require
1
modification. In fact,
manual approaches would require the modification of all the
configuration files. The proposed approach would require mod-
ification of the translation file, only, as the configuration files
will be updated automatically by a subsequent execution of the
automation mechanism. The second scenario involves changing
a feature for a subset of existing products in the SPL. In the
context of the Aventra SPL, this could be requiring that all the
LOT trains would switch from having two doors per car to four
doors per car. This scenario requires the modification of the
configuration files of the involved products, only. If
k
is the
number of the products in the subset being modified, manual
approaches would require the modification of
k
configuration
files, while the proposed approach would require
1
modification
for modifying the constraint related to the feature. The third
scenario involves the addition of a new product to the SPL. This
scenario has two sub-scenario. In the first sub-scenario, the
product is added with the same set of features as the existing
ones. In the Aventra context, this sub-scenario could be to
have a LOT train with 10 cars. This scenario would require the
creation of the configuration file for the new product. Manual
approaches would require the manual creation of one configu-
ration file, while the proposed approach would not require any
manual modification as the new product would be captured by
the variability model prior to the generation phase. The second
sub-scenario is when the new product is added with additional
features. In the Aventra context, an example of this scenario
could be a customer requiring a LOT train with 10 cars and a
new maximum speed of 300kph/186mph. This scenario would
require the modification of all the configuration files. If
n
is
the number of products in the SPL, manual approaches would
require
n
modifications, while the proposed approach would
require the modification of the translation file, only.
We have performed expert interviews for assessing the indus-
trial relevance of the proposed approach and collecting feedback
on perceived benefits and drawbacks. The questionnaire encom-
passes thirteen questions being a mix of open-ended and closed-
ended questions. The questions assessing the industrial rele-
vance draw on the model for assessing the industrial relevance
of technology transfers introduced by Ivarsson et al. (Ivarsson
& Gorschek 2011). This model focuses on four aspects being
subjects, context, scale, and research method. The survey was
shared with the engineers from the BT Aventra development
team and we got six respondents. For the sake of space, we omit
the list of the questions, which can be found here.
5
To sum up,
66,7% of the respondents have found the problem of manually
creating configuration files to be relevant and 16,7% extremely
relevant (on a scale from not relevant at all to extremely rel-
evant). One respondent has said that: this is a problem that
will only be more extensive in the future, when trying to pro-
vide generic software”. When asked about the suitability of the
proposed approach, 83,4% of the respondents found it to be
suitable (on a scale from not suitable at all to extremely suit-
able). Some of the perceived benefits are: “easy to maintain and
extend”, “this approach can improve quality of Aventra software
deliveries: reducing time for generating the configuration files,
mitigating risk for a failure, etc.”. Among the main drawbacks,
the respondents have identified that: “in the (unlikely) event
of major changes in the parameters, the feature model and the
automation pipeline could require huge and time consuming
refactoring” and “ challenging to have it reused in other do-
mains/projects”. When evaluating the industrial relevance of
the proposed approach, 83,7% of the respondents have found
the subjects, the context, the method, and the scale aspects to
be industrially relevant.
5https://zenodo.org/record/4737049#.YJFAXC0Rrxg
10 Ferko et al.
4.1. Threats to Validity
Hereafter, we discuss and classify potential threats to validity
and describe our mitigation strategies according to the scheme
proposed by Runeson et al. (Runeson & Höst 2009). The work
presented in this experience report is an example of applied
research. According to Wohlin et al., the threats to validity
for applied researches can be prioritised as follow (from the
most to the least important): internal, external, construct, and
conclusion validity (Wohlin et al. 2012).
4.1.1. Internal Validity
Threats to internal validity affect
the ability to draw correct relationships between treatment and
outcome. In order to mitigate possible threats to internal validity,
we have decided to work on a real-life example coming from our
industrial partner: the Aventra SPL. This has ensured the validity
of the artefacts and of the use case set up. When developing the
proposed approach, we have made an effort not introducing new
tools and limiting the impact of tool performance. For instance,
we have decided to measure the number of created/modified
artefacts rather than the developing or modifying time as this
could have been affected by the tools and underlying hardware.
Although we have used only a single group, we believe this did
not affect the response of the subjects involved as all of them had
prior and established experience in BT and SPL development.
4.1.2. External Validity
Threats to external validity affect
the ability to generalise the results beyond the experiment set-
tings. In order to mitigate such threats, we have made an effort
for selecting the most representative subjects. Within BT, we
have only had subjects that had prior experience with SPL de-
velopment. When it comes to the selection of the use case, we
have referred to the real-world use case from BT being the Aven-
tra SPL. The Aventra SPL was among the latest SPLs being
developed at BT. We have designed, developed, and applied
the proposed mechanism within the BT premises within the
same context where the production takes place. Eventually, we
have proposed a discussion for each step composing the pro-
posed approach for adapting it in different scenarios as a way
of generalising the finding of this research.
4.1.3. Construct Validity
Threats to construct validity re-
late to the extent to which the setting of an experiment reflects
the theory. In order to mitigate such threats, we have tried to
evaluate different aspects of the proposed approach as opposite
in focusing on one single factor. Besides, we have comple-
mented the evaluation with a qualitative survey. The design,
development, and application of the proposed approach have
been carried out within BT and using a real-world example.
When preparing the questionnaire, we have made an effort in
avoiding any possible hypothesis guess and treatment testing.
4.1.4. Conclusion Validity
Threats to conclusion validity
affect the ability to derive a correct conclusion from the rela-
tions between treatment and outcome. To minimise threats to
conclusion validity, we have asked independent practitioners to
analyse the outcome of our experience report. Besides, we have
made an effort in evaluating the proposed mechanism using
objective measures as in the case of the number of artefacts. We
have found the number of artefacts to be more reliable since
it does not involve human skills. When constructing the quali-
tative questionnaire, we have tried to use simple wording and
have remained available for possible explanations. Eventually,
we have submitted the questionnaire only to the BT engineers
having a proven experience in SPL development.
5. Discussion and Lessons Learnt
In Section 2, we have introduced the proposed approach and
its steps. For each of these steps, we have identified a set
of alternatives or decisions that could potentially impact the
generation process. In this section, we discuss the benefits and
drawbacks of these alternatives with the aim of highlighting
important aspects contributing to the generalisability of the
proposed approach. In addition, we discuss our choices and
describe lessons learnt.
The first step of the proposed approach is the categorisa-
tion of features in primary and secondary features. Here the
decision is whether or not to include the secondary features in
the variability model to build in the second step. Including the
secondary features in the variability model leads to a more de-
tailed model of the SPL and enables the automatic generation of
configuration files. However, including the secondary features
can contribute to a very complex and potentially unmanage-
able variability model especially when secondary features are
the majority in the architecture. Omitting secondary features
from the variability model would reduce the complexity and the
size of the architecture leading to a more manageable model.
However, it would dramatically increase the number of manual
modifications as the secondary features and their values would
need to be added later as variation points and variations of each
product. In addition, omitting secondary features would also
hamper the specification of constraints on these features hence
the automatic generation of valid configuration files. Here the
trade-off is between completeness and manageability. The rele-
vance of such a trade-off has been stressed by an expert in the
survey: “in the (unlikely) event of a major change in the parame-
ters, the feature model could require a huge and time consuming
refactoring” In the case of the Aventra SPL, we have decided
to include the secondary features and mark them as mandatory
features in the feature model developed using FeatureIDE. In
this way, they were automatically selected for every product and
we could easily configure them and add put constraints. Our
decision was mainly affected by two factors being the level of
automation we wanted to achieve and the limited number of
secondary features for the Aventra SPL.
The second step of the proposed approach is creating the
variability model. The main decision to take is on the notation
to be used for representing the variability model hence variation
points and variants. We have identified two alternatives being
to use feature modelling or to use metamodelling. Feature mod-
elling is a well-established formalism, which has been widely
used for SPLs. The second alternative is using metamodelling
for creating an ad-hoc language. It is worth mentioning that
feature modelling is often achieved using metamodelling tech-
niques. In our experience, the crucial factors affecting this step
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 11
are the set of competencies and skills in the company and the
available resources in terms of time and costs. In the survey,
one respondent has highlighted that: “It’s not easy to find prac-
titioners with modelling skills.” Here the trade-off is between
development effort, flexibility, and prior knowledge. In the
case of the Aventra SPL, we have decided to use feature mod-
elling and the FeatureIDE tool as it was already known within
Bombardier Transportation and did not require further training.
Other reasons behind our choice were ease of use, graphical
interface, and support for SPL evolution.
The third step of the proposed approach is the categorisa-
tion of variant constraints in technical and customer-specific.
The main decision in this step is whether or not to specify
customer-specific constraints on the variability model. Spec-
ifying customer-specific and technical constraints leads to a
precise definition of products, whose configuration files can be
derived using automation mechanisms. However, this would
require more development effort for engineers to write all the
constraints and deep knowledge of the products. In addition,
this could have an impact even when a product is added or
modified as a higher number of constraints might potentially
need to be updated. Defining only technical constraints has
resulted to be a more flexible solution and supports the evolu-
tion of SPL with less effort than in the first option. Moreover,
with this approach, tasks can be easily divided through differ-
ent teams. Engineers with domain knowledge are involved in
creating technical constraints and other engineers would deal
with the customer requirements in later stages and at the product
level. In this step, the trade-off is between development effort
and completeness. In the case of Aventra SPL, we have decided
to specify only technical constraints to ease possible future ex-
tensions and to be able to separate tasks into teams with different
levels of domain knowledge and customer-specific requirements
knowledge.
The last step of the proposed approach is the generation of
configuration files. The main discussion here is how to realise
the automation mechanism. The first alternative is to use ad-
hoc transformation languages. The second alternative is to use
traditional programming languages leveraging concepts of gen-
erative programming. The first alternative can rely on a wide
set of transformation languages and supporting tools, may en-
able a round-trip process (Eramo & Bucaioni 2013), and would
seem the natural choice in the case metamodelling is used in the
second step. However, this solution comes with several prac-
tical drawbacks, including the following. Metamodeling and
transformation languages require specific skills to be mastered.
Usually, these skills are rarely found in the industry. In addition,
tools supporting transformation languages are usually not in
the technological stack of companies hence they would require
prior training to be effectively used. Finally, transformation
languages and supporting tools would need to undergo the certi-
fication processes and this is a major drawback for a company
operating in safety-critical domains such as the railway domain
as discusses in Section 2. Metamodelling and domain-specific
languages (DSLs) could have been used for creating the transla-
tion file, with a concise syntax and semantics. A simple tooling
infrastructure could have build on this language so to achieve
e.g., code completion, type checking, etc. As mentioned above,
we have decided not to use metamodelling techniques for the
lack of competencies in the company, which would have made it
difficult to maintain and evolve the automation mechanism. Be-
sides, the use of a DSL would have not improved the mappings
between parameter and features value that can not be changed in
favour of more meaningful ones as the feature technical values
come from the actual software (which in many cases is inherited
from previous related projects). Eventually, we have provided
the translation file with a default value that is added in case none
of the correct mappings is triggered. With such a mechanism,
engineers can filter all configuration files with parameters that
have a default value to find any possible inaccuracy or mistakes
when configuring the products. It should be noted that despite
we do not use external (modelling) tools, the proposed mecha-
nism still needs to undergo verification and validation activities
in accordance with the safety standards.
6. Related Work
In this section, we survey the principal strands of research that
relate to the work we present in this paper.
In the last decades, researchers and practitioners have pro-
posed several notations and approaches for representing the
variability model of SPLs along with its variability. In this
respect, one of the most used techniques is feature mod-
elling (Danilo Beuche 2006). Other commonly used techniques
are modelling and metamodelling. In their work, Fang et al.
have presented an approach for automating software derivation
where feature modelling is integrated with domain-specific mod-
elling languages for variability expression (Fang et al. 2016).
Bergen et al. in their study present a comparison of Kconfig
and Component Description Language (CDL), two variability
modelling languages that adopt the concepts of feature mod-
elling. Both languages are used in practice to describe the
variability of the Linux kernel and eCos operating system for
embedded devices, respectively (Berger et al. 2010). Compare
to our approach, the work by Fang et al. and Bergen et al. have
a narrower scope as they mostly focus on variability expression
and not on product derivation.
The work by Czarnecki et al. proposes to split the configu-
ration process into different stages. Each stage yields a feature
model where a subset of the system described on the initial
feature model can be specified. An example of this could be
to address the requirements from individual manufacturers in
the first stage while configuring product components in a later
stage. The process by Czarnecki et al. has some similarities
with Variant Constraint Categorisation in our proposed process.
Both approaches propose to split the configuration process into
stages. While correspondences between staged-configurations
and primary and secondary features can be drawn, in the general
case they are not equivalent. To the best of our understanding,
our categorisation of features is more restrictive, while in the
process by Czarnecki et al. an engineer can decide to split the
requirements in any way she wants and assign each category to
a given stage (Czarnecki et al. 2004).
12 Ferko et al.
In the domain of train signaling, Svendsen et al. (Svend-
sen et al. 2010) have proposed an approach for representing
SPLs and generating their products, which uses the interplay of
two domain-specific modelling languages being the Train Con-
trol Language and the Common Variability Language (CVL).
Vasilevskiy et al. have investigated the use of domain-specific
modellling languages for representing variability and deriving
new products (Vasilevskiy et al. 2015). In particular, they have
introduced the Base Variability Resolution language as an ex-
tension of CVL and have provided the BVR tool bundle as
a set of Eclipse plugins. The BVR tool bundle supports the
resolution, realisation, and derivation of products. The same
authors have introduced an approach to build robust realisations,
too (Vasilevskiy et al. 2016). In the scope of their work, realisa-
tions define mappings between abstract features in a feature tree
and their implementation artefacts. The goal of their approach
was to ensure that small changes in the SPL model would result
in small changes in the realisations. Although targeting product
realisation, the approaches of Svendsen et al. and Vasilevskiy
et al. use different techniques as compared to our approach.
The approach in this paper achieves product realisation using
configuration files. Besides being a possible technique, this was
a strong requirement inherited from our business partner. In the
proposed approach we use the concepts of generative program-
ming, while in their approaches Svendsen et al. and Vasilevskiy
et al. leveraged the interplay of modelling languages and code
generation.
Several works have been investigating the use of Aspect-
Oriented Programming (AOP) for product derivation. Lee et
al. (Lee et al. 2009) leverage the interplay of AOP and fea-
ture modelling for introducing automation in the product re-
alisation. Voelter and Groherin propose to use model-driven
and aspect-oriented development to support the product deriva-
tion process (Voelter & Groher 2007). Feature models and
domain-specific models are used to represent the problem and
the solution domain, while model transformations and AOP
techniques are used for the automatic manipulation of these
models leading to product realisation. Another research focus-
ing on model transformations has been presented by Tawhid
and Petrin (Tawhid & Petriu 2011). Their approach tackles
the problem of automatically generating a model for a specific
product while focusing on performance aspects. To this end,
it relies on two model-to-model transformations. The first one
uses the Atlas Transformation Language (ATL) and takes as
input a feature model of the SPL and produces a UML model
with performance annotations realised as MARTE annotations.
Starting from this model, the second transformation generates a
Layered Queueing Network (LQN) model that will be used to
analyse the performance of the SPL.
Several frameworks and commercial tools support product
configuration in the context of SPL. One such tool is Arch-
Studio an Eclipse-based development platform based on Arch-
Feature (Gharibi & Zheng 2016). ArchFeature provides for
an architectural model integrating feature specification, prod-
uct line architecture, and their relationships. This is achieved
by extending an existing XML-based architecture description
language namely xADL. xADL is mostly used for modelling
system architectures consisting of components and connections.
It includes a graphical modelling environment that visualise
relationships of feature in a SPL and supports the automatic
derivation of the products. An assessment for other frameworks
and commercial tools supporting product configuration in a
SPL such as GEARS, pure:variants , Captor, CIDE, MSVCM,
XVCL, GenArch is done in (Torres et al. 2010).
7. Conclusion and Future Work
In this experience report, we have presented our work for au-
tomating the generation of configuration files in the context of
software product lines. The proposed approach revolves around
a mechanism leveraging concepts of generative programming
and is composed of four main steps spanning through the whole
software product line development process. We have validated
the applicability of the proposed approach using an industrial
use case from the railway domain: the Bombardier Transporta-
tion Aventra train family. Besides, we have evaluated the ability
of the proposed approach of lowering the development effort
and mitigating the error proneness typical of manual approaches.
The application of the proposed approach on the Aventra train
family has shown that the development effort and the error
proneness are mitigated already for software product lines con-
taining a limited number of products and features. We have
complemented the evaluation, with a questionnaire on the Bom-
bardier engineers. We have discussed lessons learnt and, for
each of the steps of the proposed approach, we have identified a
list of factors and alternatives that could affect its adoption in
other contexts.
Future work might encompass several research directions.
One direction is to extend the translation file with a proper JSON
schema for improving drawbacks related to type-checking and
consistency. Another possible extension improving the specifica-
tion of the mappings could be to develop a domain-specific lan-
guage. Eventually, a further extension is to investigate the pos-
sibility of realising the proposed approach within FeatureIDE.
Another research direction encompasses the development of the
generation mechanism using model-transformation languages.
In particular, we are already investigating the use of the Acceleo
transformation language. Finally, we are investigating how to
automatically collect or elicit features from requirements for
enabling the automatic derivation and categorisation of features
and constraints. This could be achieved with the interplay be-
tween formal notations for the specification of requirements and
a feature mining approach.
Acknowledgments
The work in this paper is supported by the Swedish Knowledge Foun-
dation (KKS), through the projects A-CPS and MINEStrA, and by the
Swedish Governmental Agency for Innovation Systems (VINNOVA),
through the project PANORAMA.
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About the authors
Enxhi Ferko
is a PhD student at Mälardalen University (Sweden).
You can contact him at enxhi.ferko@mdh.se.her
Alessio Bucaioni
is an assistant professor at Mälardalen University
(Sweden). You can contact him at alessio.bucaioni@mdh.se.him
Jan Carlson
is a professor at Mälardalen University (Sweden). You
can contact him at jan.carlson@mdh.se.him
Zulqarnain Haider
is a software engineer at Bombardier Railway
Transportation.
Automatic Generation of Configuration Files: an Experience Report from the Railway Domain 15
... Ferko et al. [33] reported their experience from generating configuration files from the railway domain. They used feature models in combination with a translator file, which eventually produces XML configurations that describe the product, a train. ...
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