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Integrating hierarchical task analysis into model-based system design using Airbus XHTA and IBM Rational Rhapsody

Technical University of Munic h
Technical Universi t y of Munich
Department of Informatics
Department of Mechanical Engineering
For the time and ressources spent on this research, the authors thank the chair of Birgit Vogel-Heuser, Institute of Automation and Information Systems at Technical University of Munich.
[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 that are released in the Public Domain (cliparts 194773, 192787, 34189, 155107, 182517, 192858, 276861).
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.
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.
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, Mario Weiß2, Alexander Rabl3
1Technical University of Munich, Department of Informatics, Munich
2Technical University of Munich, Department of Mechanical Engineering, Munich
3Airbus Defence and Space, Human Factors Engineering and Flight Deck GE, Manching
This publication is a collaboration of the Technical University of Munich and Airbus.
Translation of XHTA to SysML Example of HTA conversion
Fig. 1. System Engineers and Human Factors Specialists working on the same project.
Airbus XHTA element
Translation in SysML
(in Structure)
Action elements with stereotype “HTAActivity”
(in Plans)
Call Behaviors (CBs)
Connection of CBs with Control Flows (CFs)
Selection & Branching
Decision- and merge nodes
Guards on CFs
Loop Flow
Begin: Merge Node, End: Decision Node
CF back to cycle‘s begin
to Anchor Flow
CF to Anchor‘s position
-Linear Flow
Interruptible region
Fork-and join nodes
-and join nodes
(nested Plans)
Activity Diagrams
CB in originating Plan to Plan-in-Plan-Activity
containing each property as a tag
Tab le 1 . Th e mappings from Airbus XHTA elements to SysML elements.
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.
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.
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.
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.
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 l e
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.
Future Work
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 Ta b le 1.
Human Factors
IBM Rational
joint work requires high
effort in communication
respect e.g.
use individual
view on
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