Formal Component-Based Semantics

One of the proposed solutions for improving the scalability of semantics of programming languages is Component-Based Semantics, introduced by Peter D. Mosses. It is expected that this framework can also be used effectively for modular meta theoretic reasoning. This paper presents a formalization of Component-Based Semantics in the theorem prover Coq. It is based on Modular SOS, a variant of SOS, and makes essential use of dependent types, while profiting from type classes. This formalization constitutes a contribution towards modular meta theoretic formalizations in theorem provers. As a small example, a modular proof of determinism of a mini-language is developed.Comment: In Proceedings SOS 2011, arXiv:1108.279

CoFI: The Common Framework Initiative for Algebraic Specification and Development

An open collaborative effort has been initiated: to design acommon framework for algebraic specification and development of software. The rationale behind this initiative is that the lack of such a common framework greatly hinders the dissemination and application of researchresults in algebraic specification. In particular, the proliferationof specification languages, some differing in only quite minor ways from each other, is a considerable obstacle for the use of algebraic methods in industrial contexts, making it difficult to exploit standard examples, case studies and training material. A common framework with widespread acceptancethroughout the research community is urgently needed.The aim is to base the common framework as much as possible on a critical selection of features that have already been explored in various contexts. The common framework will provide a family of specificationlanguages at different levels: a central, reasonably expressive language, called CASL, for specifying (requirements, design, and architecture of) conventional software; restrictions of CASL to simpler languages, for use primarily in connection with prototyping and verification tools; and extensionsof CASL, oriented towards particular programming paradigms,such as reactive systems and object-based systems. It should also be possibleto embed many existing algebraic specification languages in members of the CASL family. A tentative design for CASL has already been proposed. Task groupsare studying its formal semantics, tool support, methodology, and other aspects, in preparation for the finalization of the design

Theory and Practice of Action Semantics

Action Semantics is a framework for the formal descriptionof programming languages. Its main advantage over other frameworksis pragmatic: action-semantic descriptions (ASDs) scale up smoothly torealistic programming languages. This is due to the inherent extensibilityand modifiability of ASDs, ensuring that extensions and changes tothe described language require only proportionate changes in its description.(In denotational or operational semantics, adding an unforeseenconstruct to a language may require a reformulation of the entire description.)After sketching the background for the development of action semantics,we summarize the main ideas of the framework, and provide a simpleillustrative example of an ASD. We identify which features of ASDsare crucial for good pragmatics. Then we explain the foundations ofaction semantics, and survey recent advances in its theory and practicalapplications. Finally, we assess the prospects for further developmentand use of action semantics.The action semantics framework was initially developed at the Universityof Aarhus by the present author, in collaboration with David Watt(University of Glasgow). Groups and individuals scattered around fivecontinents have since contributed to its theory and practice

CASL for ASF+SDF Users

Casl is an expressive language for the algebraic specificationof software requirements, design, and architecture. It has beendeveloped by an open collaborative effort called CoFI (CommonFramework Initiative for algebraic specification and development).Casl combines the best features of many previous algebraic specification languages, and it is hoped that it may provide a focus for future research and development in the use of algebraic techniques, as well being attractive for industrial use.This paper presents Casl for users of the Asf+Sdf framework.It shows how familiar constructs of Asf+Sdf may bewritten in Casl, and considers some problems that may arisewhen translating specifications from Asf+Sdf to Casl. It thenexplains and motivates various Casl constructs that cannot beexpressed directly in Asf+Sdf. Finally, it discusses the role thatthe Asf+Sdf system might play in connection with tool supportfor Casl

On the Action Semantics of Concurrent Programming Languages

Action semantics is a framework for semantic description of prograrnming languages. In this framework, actions are semantic entities, used to represent the potential behaviour of programs --- also the contributions that parts of programs make to such behaviour. The notation for expressing actions, called action notation, is combinator-based. It is used in much the same way that lambda-notation is used in denotational semantics. However, the essence of action notation is operational, rather than mathematical, and its meaning is formally defined by a structural operational semantics together with a bisimulation equivalence.This paper briefly motivates action semantics, and explains the basic concepts. It then illustrates the use of the framework by giving an action semantic description of a small example language. This language includes a simple form of concurrency: tasks that may synchronize by means of rendezvous. The paper also discusses the operational semantics of action notation, focusing on the primitive actions that represent asynchronous message transmission and process initiation

CASL for CafeOBJ Users

Casl is an expressive language for the algebraic specificationof software requirements, design, and architecture. It has been developed by an open collaborative effort called CoFI (Common Framework Initiative for algebraic specification and development). Casl combines the best features of many previous main-stream algebraic specification languages, and it should provide a focus for future research and development in the use of algebraic techniques, as well facilitating interoperability ofexisting and future tools. This paper presents Casl for users of the CafeOBJ framework, focusing on the relationship between the two languages. It first considers those constructs of CafeOBJ that have direct counterparts in Casl, and then (briefly) those that do not. It also motivates various Casl constructsthat are not provided by CafeOBJ. Finally, it gives a concise overview of Casl, and illustrates how some CafeOBJ specifications may be expressed in Casl

Exploiting Labels in Structural Operational Semantics

Structural Operational Semantics (SOS) allows transitions to be labelled. This is fully exploited in SOS descriptions of concurrent systems, but usually not at all in conventional descriptions of sequential programming languages. This paper shows how the use of labels can provide significantly simpler and more modular descriptions of programming languages. However, the full power of labels is obtained only when the set of labels is made into a category, as in the recently-proposed MSOS variant of SOS

The Operational Semantics of Action Notation

Action notation is used in the action semantics fratnework, for specifying actions representing program behaviour. It is defined by a structural operational semantics together with a bisimulation-based equivalence that satisfies some simple algebraic laws