Scenario Modelling
Modelling Global Behaviour with Scenarios in Object-Oriented Analysis
DŐpartement d'Informatique, Ecole Polytechnique FŐdŐral de Lausanne,
Switzerland, May 1997
Abstract
The first object-oriented analysis methods focused on the specification of the
classes of a system and on the static relationships between them. Dynamic
relationships between classes and the functional view of the system as a whole
were neglected, and no models were offered for capturing system requirements.
This changed with the publication of use case driven approaches such as OOSE
(1992) and Fusion (1994). Modelling global behaviour by scenarios in both
requirements analysis and design has since been adopted by many
object-oriented methods. Scenarios are also called use cases, system
operations or business processes, and they are modelled using different
notations.
Some of the analysis methods that use scenarios have common characteristics,
namely i) the similarity of the relationship between the entities of a data
model and the scenarios of a flat scenario model with a matrix, and ii) the
assumption that the externally visible behaviour of the system can be
subdivided into more or less independent scenario types. In the following, we
will refer to these characteristics by the term matrix approach. While in many
projects the matrix approach has been used successfully, several difficul ties
arise when more complex systems are modelled: relationships and similarities
between different scenario types cannot be expressed, the dependencies between
scenario types are not modelled, only one abstraction level can be
represented, and the apparently seamless transition from the analysis to the
design model may result in a low quality object model with a strong bias
towards data modelling.
These difficulties lead us to propose an enhanced scenario modelling technique
(called SEAM) which overcomes some of the weaknesses of the matrix approach.
This modelling technique includes composition, aggregation, specialisation and
extension hierarchies of services, and is based on the paradigm of interacting
objects (which can be
atomic objects, subsystems or systems) offering services. Scenario types,
showing the possible interaction sequences for a specific service, can be
modelled on several abstraction levels, and can describe the services of any
kind of object (and thus also the global behaviour of a whole system) from
both an internal and external point of view. We describe the concepts and the
notation of SEAM, and we show how it can be integrated into the Fusion method.
The difficulties that may arise in projects using methods based on the matrix
approach are not only due to the limitations of scenario modelling techniques.
A major factor is the often contradictory definition of the analysis model
goals, which leads to clashes of intent. Therefore we discuss the nature of
such intent clashes and analyse how the different software development methods
deal with them.
Finally we give an overview of the various notations and basic concepts used
by different scenario modelling techniques, and we provide summaries of
current, mostly object-oriented, approaches to modelling global behaviour.
Keywords
scenario, scenarios, object-oriented analysis, interaction diagram,
use case, use cases use-case, use-cases, behaviour, behavior,
scenario modelling, methodology, object-oriented method
Thesis
You can download the thesis:
whole thesis (24 MB)
whole thesis (compressed, 2.8 MB)
whole thesis (gnuzip, 2.2 MB)
whole thesis, large font (24 MB)
abstracts, tables of contents,
references (compressed, 71 kB)
chapters 1-3 (compressed, 0.3 MB)
chapters 4-6 (compressed, 0.8 MB)
appendix (compressed, 1.6 MB)
In order to get a paper copy of the thesis contact the secretary of the Software Engineering Laboratory of the EPFL.
Talks
Presentation of the thesis
Modelling with scenarios
Page last modified: May 20, 1997 by DBR