Behavioral Refinement of Software Architectures

Formal methods are mathematical techniques which aim at introducing sound engineering principles into software development. Especially in early development phases, where the overall structure of a software system — also called its software architecture — is designed, formal methods help to avoid errors. Therefore, a lot of formal methods based research has been and still is undertaken in the field of software architecture. Architecture specification languages have been developed and formally defined, architectural styles have been specified precisely, and architectural refinements have been rigorously analyzed. This thesis aims at improving the development of software architectures by investigating their behavioral refinement. Up to now, formal analysis of architectural refinements has been based on structure-preserving relations which allow a compositional development. Unfortunately, these formal refinements are not sufficient for the development of architectures. This claim is demonstrated by modeling the behavior of architectures using the formal specification language LOTOS and the temporal logic ACTL, and by analyzing properties of refinements with model-checking techniques. Based on the analysis results, an architectural refinement defined by a set of temporal formulae is proposed. We call such a refinement a non-formal one, because it is not possible to define a formal, structure-preserving relation for it. Unfortunately, non-formal refinement is not fully compositional any more. To overcome this problem, a catalog of architectural patterns and their refinements with formally preanalyzed properties is presented. These patterns help the developer to make more wellfounded design decisions in the architectural development phase. Furthermore, the findings of this thesis form a basis for the enhancement of architectural languages and their tools.