Amalgamation in the semantics of CASL

We present a semantics for architectural specifications in the Common Algebraic Specification Language (Casl), including an extended static analysis compatible with model-theoretic requirements. The main obstacle here is the lack of amalgamation for Casl models. To circumvent this problem, we extend the Casl logic by introducing enriched signatures, where subsort embeddings form a category rather than just a preorder. The extended model functor satisfies the amalgamation property as well as its converse, which makes it possible to express the amalgamability conditions in the semantic rules in static terms. Using these concepts, we develop the semantics at various levels in an institution-independent fashion. Moreover, amalgamation for enriched Casl means that a variety of results for institutions with amalgamation, such as computation of normal forms and theorem proving for structured specifications, can now be used for Casl.     

CoCasl at Work — Modelling Process Algebra

CoCasl[11], a recently developed coalgebraic extension of the algebraic specification language Casl[2], allows for modelling systems in terms of inductive datatypes as well as of co-inductive process types. Here, we demonstrate how to specify process algebras, namely CCS[10] and CSP[8,17], within such an algebraic-coalgebraic framework. It turns out that CoCasl can deal with the fundamental concepts of process algebra in a natural way: The type system of communications, the syntax of processes and their structural operational semantics fit well in the algebraic world of Casl, while the additional coalgebraic constructs of CoCasl cover the various process equivalences (bisimulation, weak bisimulation, observational congruence, and trace equivalence) and provide fully abstract semantic domains. CoCasl hence becomes a meta-framework for studying the semantics and proof theory of reactive systems.     

Higher-Order Nets for Mobile Policies

Since the early 80's the combination of Petri nets and rule-based transformations has been extensively researched to obtain new concepts and results. In this paper we consider rules as tokens leading to the concept of higher-order nets for mobile policies. The rules are used on the one hand for the specification of policy rules and on the other hand for the modification of policy rules, i.e. for the definition of new rules by reusing existing rules. So the higher-order net models distribution and modification of policy rules in a systematic and structured way. We give HasCasl-specifications of rules and (local) transformations in the sense of the double-pushout approach and illustrate our concept by a small system inspired by the case study of a tax refund process [E. Bertino, E. Ferrari, E., and V. Atluri. The Specification and Enforcement of Authorization Constraints in Workflow Management Systems. ACM Transactions on Information and System Security 2 (1) (1999) 65–104].     

Algebraic–coalgebraic specification in CoCasl

We introduce CoCasl as a light-weight but expressive coalgebraic extension of the algebraic specification language Casl. CoCasl allows the nested combination of algebraic datatypes and coalgebraic process types. Moreover, it provides syntactic sugar for an observer-indexed modal logic that allows e.g. expressing fairness properties. This logic includes a generic definition of modal operators for observers with structured equational result types. We prove existence of final models for specifications in a format that allows the use of equationally specified initial datatypes as observations, as well as modal axioms. The use of CoCasl is illustrated by specifications of the process algebras CSP and CCS.