Specification of Reactive Hardware/Software Systems - Electronic ...

230 Introduction to the Semantics of POOSL
7.1 Introduction
In the previous Chapters 4,5 and 6 the method concepts that constitute the SHE method
were described in detail. Recall that the SHE method starts off with informal modelling
and gradually produces rigorous specifications described in the formal specification
language POOSL[Voe94, Voe95a, Voe95b]. This means that during the process of specification,
the method concepts are mapped little by little onto the formal (syntactic)
language primitives of POOSL 1 . For instance:
All types of message flows are basically mapped onto the pair-wise synchronous
message passing primitive. Sometimes, for instance in case of the interrupt flow,
other primitives are also required.
Architecture structure and topology is mapped onto process object primitives,
cluster primitives and channel primitives.
Clusters that carry boundaries are mapped onto cluster primitives.
Attributes and conceptual relations in Object Class Diagrams are basically mapped
onto instance variable primitives.
Scenario narratives and the corresponding Message Flow Diagrams are mapped
onto behaviour description primitives.
Carrying out the mapping from concepts onto the language primitives is called formalisation.
The way the different method concepts are formalised is explained in Chapters
4,5 and 6. In this and the following chapters, the focus will be on the POOSL language
and its supporting language primitives.
The language POOSL as well as the backgrounds of its development is described in
Chapters 8 and 9. This chapter gives a brief characterisation of the language. It explains
the reasons why we developed a formal language. It further introduces some basic
mathematics that is assumed to be known in Chapters 8, 9 and 10.
7.2 A Brief Language Characterisation
Process Objects
A specification in POOSL consists of a fixed set of process objects and process-object
clusters, which are composed by parallel composition, channel hiding and channel
renaming. For convenience we will often use the terms processes and clusters to denote
process objects respectively process-object clusters. Processes and clusters are statically
interconnected in a topology of channels, through which they can communicate by
exchanging messages. Message exchange is based upon the synchronous (rendezvous)
pair-wise message-passing mechanism of CCS [Mil80, Mil89].
1 In general, it may take several language primitives to express a single concept. On the other hand,
some particular primitive may be required to express different concepts. See also Section 9.7