paper - Universität Rostock

constructed on the basis of the task model in Fig.1 and revealed the sub-action rechecking the total
list which was added afterwards to the task model (indicated with dotted lines in the figure). “In
SBD new activities are always grounded in current activities” [RC02]. Scenarios as stories support
the transition from current to envisioned models. Taken the scenario in Sect.2, for example, one
can easily imagine that in the envisioned practice the compiling of the total list out of the single
lists for each of the 5 exercises can be done automatically by the software system under
development. It is also of advantage that the system can label the “borderline cases” (the entries of
the students who miss 1 or 2 points to pass the examination). An envisioned task model has to
reflect the application of the software system by the actors.
problem
scenarios
...
task model of the
current practice
specification
of the software
system
design
scenarios
...
task model of the
envisioned practice
test case
scenarios
...
Figure 3: A combination of MBD and SBD
Scenarios as test cases are complete scenarios in the sense of Sect. 4.1. They can be generated
from sub-trees of the action hierarchy as should be underlined by Fig.2. They are useful for
validating a system specification with respect to a task model and vice versa because they describe
the interaction between a user and the system precisely. Scenarios of this kind are rather
comparable with scenarios as paths through use cases.
Fig.3 illustrates possible applications of scenarios to supplement a model-based design process.
5 Summary
A combination of SBD and MBD to improve the software design process was shown. Task
models play a mediating role. They supply a general description which is useful for constructing
scenarios on the one side but also for deriving formal system specifications on the other side. A
distinction between scenarios as stories and scenarios as test cases was proposed and their
different fields of application were explored. There are a lot of open questions. The problem of
choosing a representative set of test case scenarios out of a possibly infinite set is only one of
them. The interested reader is referred to [FD03] where tool support is described.
References
[Car02] J.M.Carroll: Scenarios and Design Cognition, Proc. of the Int. Conf. On Requirements
Engineering RE2002, Essen, Germany.
[RC02] M.B.Rosson, J.M.Carroll: Usability Engineering – Scenario-Based Development of
Human-Computer Interaction, Morgan Kaufmann Publishers, 2002.
[FD03] P.Forbrig, A.Dittmar: Interfacing Business Object and User Models with Action Models
in this Proceedings of HCI 2003.
[Dit02] A.Dittmar: Ein formales Metamodell für den aufgabenbasierten Entwurf interaktiver
Systeme, PhD-Thesis, Universität Rostock, 2002.