Distributed systems : architecture-driven specification using extended LOTOS

Abstract

The thesis uses the LOTOS language (ISO International Standard ISO 8807) as a basis for the formal specification of distributed systems. Contributions are made to two key research areas: architecture-driven specification and LOTOS language extensions. The notion of architecture-driven specification is to guide the specification process by providing a reference-base of pre-defined domain-specific components. The thesis builds an infra-structure of architectural elements, and provides Extended LOTOS (XL) definitions of these elements. The thesis develops Extended LOTOS (XI.) for the specification of distributed systems. XL- is LOTOS enhanced with features for the formal specification of quantitative timing. probabilistic and priority requirements. For distributed systems, the specification of these ‘performance’ requirements, ran be as important as the specification of the associated functional requirements. To support quantitative timing features, the XL semantics define a global, discrete clock which can be used both to force events to occur at specific times, and to measure Intervals between event occurrences. XL introduces time policy operators ASAP (as soon as possible’ corresponding to “maximal progress semantics") and ALAP (late as possible'). Special internal transitions are introduced in XL semantics for the specification of probability, Conformance relations based on a notion of probabilization, together with a testing framework, are defined to support reasoning about probabilistic XL specifications. Priority within the XL semantics ensures that permitted events with the highest priority weighting of their class are allowed first. Both functional and performance specification play important roles in CIM (Computer Integrated Manufacturing) systems. The thesis uses a CIM system known as the CIM- OSA lntegrating Infrastructure as a case study of architecture-driven specification using XL. The thesis thus constitutes a step in the evolution of distributed system specification methods that have both an architectural basis and a formal basis.