One of the main research objectives of computer science is the development of formal methods for the design and implementation of programming languages. This research area has witnessed a proliferation of concepts, models and methods. However, the problem of the relative expressive power of the various programming concepts has rarely been addressed systematically.

A systematic study and a formal comparison is even more needed in the case of formalisms for programming or specifying parallel and distributed systems. This study is indispensable for classifying the different programming languages and for providing a formal basis for design principles and implementation techniques of concurrent and/or distributed programming languages.

The main aim of the seminar, organized within the program of the HCM-network EXPRESS, was a better understanding of the interconnections and relations between programming concepts, constructs, models and logics for concurrent specification and implementation languages. The final objective of the project is the definition of a general framework for the comparison of the formal methods for specification and verification developed within the various programming paradigms, in particular with a focus on process algebras. The seminar gave the possibility to compare results of the project with related approaches.

The different talks and the lively discussion offered the occasion for comparing specification and verification methods, developed various programming paradigms, and threw light on:

• the primitives for communication (synchronous vs asynchronous) and nondeterministic choice (internal vs external);
• the different stress on causal and temporal dependencies offered by the various semantic models (process algebras, Petri nets, modal logics, rewrite systems),
• the relative merits of the different approaches to concurrent systems semantics (algebraic, axiomatic, operational, denotational).

The program of the seminar was intense and stimulating; it comprised 30 talks, the abstracts of which are recorded in the Dagstuhl-Seminar-Report in alphabetical order.

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