This work describes the formal semantics of SCHEME 1 as an equational theory in the MAUDE rewriting system. The semantics is based on continuations and is highly modular. We briefly investigate the relationship between our methodology for defining programming languages and other semantic formalisms. We conclude by showing some performance results of the interpreter obtained for free from the executable specification.

In 1981 Structural Operational Semantics (SOS) was introduced as a systematic way to define operational semantics of programming languages by a set of rules of a certain shape [62]. Subsequently, the format of SOS rules became the object of study. Using so-called Transition System Specifications (TSS’s) several authors syntactically restricted the format of rules and showed several useful properties about the semantics induced by any TSS adhering to the format. This has resulted in a line of research proposing several syntactical rule formats and associated meta-theorems. Properties that are guaranteed by such rule formats range from well-definedness of the operational semantics and compositionality of behavioral equivalences to security- and probability-related issues. In this paper, we provide an initial hierarchy of SOS rules formats and meta-theorems formulated around them.

These notes give an overview of the main frameworks that have been developed for specifying the formal semantics of programming languages. Some of the pragmatic aspects of semantic descriptions are discussed, including modularity, and potential applicability to visual and modelling languages. References to the literature provide starting points for further study.

In 1981 Structural Operational Semantics (SOS) was introduced as a systematic way to define operational semantics of programming languages by a set of rules of a certain shape [G.D. Plotkin, A structural approach to operational semantics, Technical

Bialgebraic semantics, invented a decade ago by Turi and Plotkin, is an approach to formal reasoning about well-behaved structural operational specifications. An extension of algebraic and coalgebraic methods, it abstracts from concrete notions of syntax and system behaviour, thus treating various kinds of operational descriptions in a uniform fashion. In this talk, the current state of the art in the area of bialgebraic semantics is presented, and its prospects for the future are sketched. In particular, a combination of basic bialgebraic techniques with a categorical approach to modal logic is described, as an abstract approach to proving compositionality by decomposing modal logics over structural operational specifications. Keywords:

Abstract: Most approaches to formal semantics are based on the assumption that all the constructs of a language are defined together. The details of the definition of each construct can (and usually do) depend on which other constructs are included in the given language. This limits reuse of definitions of common constructs. programming construct is defined separately and independently. The semantics of a full language is obtained by translating its constructs into the basic abstract constructs, whose definitions are thus reused verbatim. The frameworks of Modular SOS and Action Semantics can both be used in conjunction with the proposed approach. Some illustrations are given. Key Words: semantics of programming languages, action semantics, structural operational semantics, modularity

We present a prototype implementation of SOS meta-theory in the Maude term rewriting language. The prototype defines the basic concepts of SOS meta-theory (e.g., transition formulae, deduction rules and transition system specifications) in Maude. Besides the basic definitions, we implement methods for checking the premises of some SOS meta-theorems (e.g., GSOS congruence meta-theorem) in this framework. Furthermore, we define a generic strategy for animating programs and models for semantic specifications in our meta-language. The general goal of this line of research is to develop a general-purpose tool that assists language designers by checking useful properties about the language under definition and by providing a rapid prototyping environment for scrutinizing the actual behavior of programs according to the defined semantics.

Strategies are a powerful mechanism to control rule application in rule-based systems. For instance, different transition relations can be defined and then combined by means of strategies, giving rise to an effective tool to define the semantics of programming languages. We have endowed the Maude MSOS Tool (MMT), an executable environment for modular structural operational semantics, with the possibility of defining strategies over its transition rules, by combining MMT with the Maude strategy language interpreter prototype. The combination was possible due to Maude’s reflective capabilities. One possible use of MMT with strategies is to execute Ordered SOS specifications. We show how a particular form of strategy can be defined to represent an OSOS order and therefore execute, for instance, SOS specifications with negative premises. In this context, we also discuss how two known techniques for the representation of negative premises in OSOS become simplified in our setting.

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Orc is a language for orchestration of web services developed by J. Misra that offers simple, yet powerful and elegant, constructs to succinctly program sophisticated web orchestration applications. However, because of its real-time nature and the different priorities given to internal and external events in an Orc program, giving a formal operational semantics that captures the real-time behavior of Orc programs is nontrivial and poses some interesting challenges. In this report, we first propose a realtime operational Orc semantics, that captures the informal operational semantics given in [26]. This operational semantics is given as a rewrite theory R sos Orc in which the elapse of time is explicitly modeled. This is followed by presenting a much more efficient reduction semantics of Orc, which is provably equivalent to the SOS semantics. A detailed proof of strong bisimilarity of the two semantic specifications is then given. In both