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Hierarchical Task Analysis (HTA) is awidely used method in
Human Factors to investigate human work by decomposing
tasks into goal-task-subgoal-structures (Stanton et al., 2017).
Knowledge about goals, tasks and actions of human work is
fundamental to many further activities like system design,
human-machine-task allocation and interface design (Hackos
and Redish, 1998)as well as a prerequisite for different
subsequent analysis methods for e.g. safety purposes.
A systems engineer needs to know and understand these
results of Human Factor specialists analyses in order to
respect them in the system design.
[Hackos and Redish, 1998] Hackos, JoAnn T., and Redish, Janice. “User and task analysis for interface design.”, 1998.
[Rabl et al., 2018] Rabl, Alexander N., et al. “DONT PANIC! Perform Complex Hierarchical Task Analysis with the Airbus eXtended HTA tool” in Proceedings of the
33rd Conference of the European Association of Aviation Psychology, 2018.
[Stanton et al., 2017] Stanton, Neville A., et al. “Human Factors Methods: a Practical Guide for Engineering and Design.” Taylor and Francis, 2017.
Fig. 1 uses graphics from openclipart.org that are released in the Public Domain (cliparts 194773, 192787, 34189, 155107, 182517, 192858, 276861).
According to Rabl et al. (2018) a Hierarchical Task
Analysis in Airbus XHTA consists of two seperate parts,
one single Structure and one or multiple Plans.
The structure represents the strictly hierarchical
relationship of goals, tasks and actions. All subelements
of a certain level are either neccessary and/or sufficient
to achieve the target state of said level. In Airbus XHTA
Plans, all elements of the Structure are connected by
different logical flow controls in order to create a activity-
diagram like overview of the goal-task structures.
Integrating Hierarchical Task Analysis into Model-Based System
Design using Airbus XHTA and IBM Rational Rhapsody
Jakob Rott1, Julian Weixler1, Alexander Rabl2, Peter Sandl2, Mario Weiß3, Birgit Vogel-Heuser3
1Technical University of Munich, Department of Informatics, Munich, Germany
2Airbus Defence and Space, Human Factors Engineering and Flight Deck GE, Manching, Germany
3 Technical University of Munich, Department of Mechanical Engineering, Munich, Germany
Introduction
Translation of XHTA to SysML Example of HTA conversion
Airbus
XHTA
System
Engineers
Human Factors
Specialists
IBM Rational
Rhapsody
joint work requires high
effort in communication
respect e.g.
psychologic
al effects
use individual
software
holistic
view on
system
use
standard
software
Fig. 1. System Engineers and Human Factors Specialists working on the same project.
References
Conclusion
The HTA Converter offers a possibilty to covert HTAs to a SysML representation. The specialized data model of Airbus XHTA
is persisted in a standardized language.This work can have an impact on system engineering to ensure Human Factors
findings are adequately respected and eases the communication between the involved system engineering disciplines.
Future Work
In modern projects the traditional document based
specifications are often replaced by Model Based System
Engineering (MBSE).Due to different applications used
by Human Factors specialists and system engineers prior
to this study it was difficult to integrate the results of HTA
in the model based system engineering process.
We present a new tool called HTA Converter to integrate a
Hierarchical Task Analysis defined in Airbus XHTA into an
IBM Rational Rhapsody project to bridge the tooling gap
between the different departments.This has advantages
for the development process and can lead to better
products that are easier to operate even under very
difficult conditions.
For both,the Structure as well as the Plans, a direct
mapping was established linking XHTA logical elements
to IBM Rational Rhapsody SysML elements (see Tab le
1). To recreate the Structure, a block definition diagram
was utilised. To mirror XHTAs Plans, SysML Activity
diagrams were employed (see Figure 3).
The mapping of XHTA to IBM Rational Rhapsody models
formally mirrors all data,the Human Factors Analyst has
brought into the model.Yet,we want to assess the
benefits of importing HTA results in system engineering
tools both on the level of the Human Factors as well as
on the systems engineering process.
Further, modeling tools beside IBM Rational Rhapsody
should be supported. This way,the knowledge about
human work can be dispersed in abroader way and aid
system design more holistically.
IEEM18-P-0259
Fig. 2. Upper picture shows the Structure of an HTA in Airbus XHTA. Lower Picture is the translation in IBM
Rational Rhapsody using a Block Definition Diagram.
The example illustrates a simplified HTA Fuel Imbalance containing
tasks regarding the situation of imbalenced fuel levels. The
hierarchical Structure of the HTA as visualized in Airbus XHTA is
shown in Figure 2upper picture. The Structure on the level below
the main task consists of six tasks.
After importing the output XML file
generated by the HTA Converter in IBM
Rhapsody, the user can create a Block
Definition Diagram (BDD) and include the
Structure elements.The BDD then
contains all tasks created in the XHTA
Structure with their hierarchy illustrated
by composition relations (Fig.2,lower).
The Plan (Fig.3,left)of the sample HTA
is converted to an activity diagram (Fig. 3,
right). For each reference from an
element in the Plan to the corresponding
task in the Structure a Call Behavior is
created as described in Tab le 1.
Fig. 3. Left picture shows a plan of a sample project in Airbus XHTA. The right picture shows the same plan
converted to an activity diagram in IBM Rational Rhapsody.
Airbus XHTA element
Translation in SysML
Tasks
(in Structure)
Action elements with stereotype “HTAActivity”
Plans
(general)
Activity
Diagrams
Tasks
(in Plans)
Call Behaviors (CBs)
Linear
Flow
Connection of CBs with Control Flows (CFs)
Selection & Branching
Flow
–
Decision- and merge nodes
–
Guards on CFs
Cyclic
Loop Flow
–
Begin: Merge Node, End: Decision Node
–
CF back to cycle‘s begin
Jump
to Anchor Flow
CF to Anchor‘s position
Non
-Linear Flow
–
Interruptible region
–
Fork-and join nodes
Parallel
Flow
Fork
-and join nodes
Plan
-in-Plan
(nested Plans)
–
Activity Diagrams
–
CB in originating Plan to Plan-in-Plan-Activity
Diagram
Properties
Stereotype
containing each property as a tag
Tab l e 1. T h e mappings from Airbus XHTA elements to SysML elements.