Abstract

Use cases are widely recognized as useful tools for describing user
requirements. Because they are represented informally, use cases permit
user participation in and are conducive to the creativity needed for
requirements elicitation and analysis. However, the representation of a
system by a collection of use cases has disadvantages. For instance,
because system description is spread over many small models, changing
one use case requires to visit all use cases to determine whether the
change affects them. This problem is exacerbated by the difficulty of
consistency check between use cases. Furthermore, such a model does not
show the starting and terminating contexts of the use cases, nor is it
easy denote the relationships between them.

LOTOS is a mathematically based specification language developed within
the framework of ISO standardization for the specification of OSI
services and protocols. This thesis presents a method for transforming
system descriptions in the form of scenarios (defined as collections of
causally-ordered internal and external events) into `unified' LOTOS
specifications. This transformation eliminates some of the undesirable
properties associated with describing a system with scenarios, and
bridges the gap between early informal requirements and formal
LOTOS-based development processes. Moreover, it describes a system's
structure in the same model as its behaviors. The crux of this method
is the integration of scenarios. Our proposed method performs
integration at the semi-formal level and uses LOTOS operators for the
integration. 

The method was derived by a posteriori rationalization of the process
followed to specify the European standard for the Global System for
Mobile Communications (GSM). Thus, GSM itself and its specification in
LOTOS are discussed. The thesis also reports results for automatic
regeneration of scenarios from LOTOS specifications as well as a
technique for determining whether or not a specification contains a
given scenario.