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

6.7 Real-Time Modelling 223
claimed. At any time the behaviour can be aborted by the reception of a release message.
Such a message must contain both the identifier of the object and the identifier of the
requester that is releasing the object. The check of the correctness of both identifiers
guarantees that the release message is only accepted by the right object, even if there are
various multiples and requesters on a channel.
6.6.8.7 Summary
The description of the modelling of dynamic behaviour completed the description of
the concepts of data object, process object, cluster and system. Various concepts to
reason about state on various levels of abstraction have been defined. They support
the description of dynamic behaviour. Named states represent behaviour that produces
responses on messages that represent events. This approach integrates aspects of event
orientation found in Structured Analysis with the object-orientated paradigm.
Our method can describe very complex parallel systems with an infinite state space. We
presented an introduction to the expressions and statements that POOSL offers for the
definition of data classes, process classes, cluster classes and systems.
Data objects enable the description of dynamic data structures. Data is stored in instance
variables and local variables. By receiving messages corresponding methods are
activated. The interaction of data objects is sequential. The various statements such as
assignment statements, ’if’ statements and ’do’ statements have been presented.
Process objects are autonomous entities that can perform concurrent and/or infinite
behaviour. Behaviour is defined as a collection of methods. Interrupt, abort and choice
statements are constructs that give our method the ability to describe systems adequately
at a high level of abstraction. Clusters and systems are described as a parallel
composition of instances of process classes and cluster classes using channel hiding and
renaming.
6.7 Real-Time Modelling
6.7.1 Introduction
A method for analysis and design of reactive hardware/software systems has limited
applicability when it does not offer appropriate concepts for the modelling of the realtime
properties of a system. This thesis focuses on the modelling of the temporal order of
events and actions without explicit specification of the time properties. The introduction
of timing concepts requires the study of a huge world of dedicated research. Therefore
we decided to make this into a separate project. The first results of this project [Gei96] are
so promising that the research is continued as a separate Ph.D. project. For this reason
we report only briefly the first results achieved and some preliminary ideas about an
approach to the modelling of (real-)time.