Modular Structural Operational Semantics

Modular SOS (MSOS) is a variant of conventional Structural Operational Semantics (SOS). Using MSOS, the transition rules for each construct of a programming language can be given incrementally, once and for all, and do not need reformulation when further constructs are added to the language. MSOS thus provides an exceptionally high degree of modularity in language descriptions, removing a shortcoming of the original SOS framework. After sketching the background and reviewing the main features of SOS, the paper explains the crucial differences between SOS and MSOS, and illustrates how MSOS descriptions are written. It also discusses standard notions of semantic equivalence based on MSOS. An appendix shows how the illustrative MSOS rules given in the paper would be formulated in conventional SOS

Foundations of Modular SOS

A novel form of labelled transition system is proposed, wherethe labels are the arrows of a category, and adjacent labels in computations are required to be composable. Such transition systems provide thefoundations for modular SOS descriptions of programming languages.Three fundamental ways of transforming label categories, analogous tomonad transformers, are provided, and it is shown that their applicationspreserve computations in modular SOS. The approach is illustrated withfragments taken from a modular SOS for ML concurrency primitives

Meta SOS - A Maude Based SOS Meta-Theory Framework

Meta SOS is a software framework designed to integrate the results from the meta-theory of structural operational semantics (SOS). These results include deriving semantic properties of language constructs just by syntactically analyzing their rule-based definition, as well as automatically deriving sound and ground-complete axiomatizations for languages, when considering a notion of behavioural equivalence. This paper describes the Meta SOS framework by blending aspects from the meta-theory of SOS, details on their implementation in Maude, and running examples.Comment: In Proceedings EXPRESS/SOS 2013, arXiv:1307.690

Logical Specification of Operational Semantics

Various logic-based frameworks have been proposed for specifying the operational semantics of programming languages and concurrent systems, including inference systems in the styles advocated byPlotkin and by Kahn, Horn logic, equational specifications, reductionsystems for evaluation contexts, rewriting logic, and tile logic.We consider the relationship between these frameworks, and assess theirrespective merits and drawbacks - especially with regard to the modularity of specifications, which is a crucial feature for scaling up to practicalapplications. We also report on recent work towards the use of the Maudesystem (which provides an efficient implementation of rewriting logic) asa meta-tool for operational semantics

Modular structural operational semantics

Modular SOS (MSOS) is a variant of conventional Structural Operational Semantics (SOS). Using MSOS, the transition rules for each construct of a programming language can be given incrementally, once and for all, and do not need reformulation when further constructs are added to the language. MSOS thus provides an exceptionally high degree of modularity in language descriptions, removing a shortcoming of the original SOS framework. After sketching the background and reviewing the main features of SOS, the paper explains the crucial differences between SOS and MSOS, and illustrates how MSOS descriptions are written. It also discusses standard notions of semantic equivalence based on MSOS. Appendix A shows how the illustrative MSOS rules given in the paper would be formulated in conventional SOS

Executable component-based semantics

The potential benefits of formal semantics are well known. However, a substantial amount of work is required to produce a complete and accurate formal semantics for a major language; and when the language evolves, large-scale revision of the semantics may be needed to reflect the changes. The investment of effort needed to produce an initial definition, and subsequently to revise it, has discouraged language developers from using formal semantics. Consequently, many major programming languages (and most domain-specific languages) do not yet have formal semantic definitions.To improve the practicality of formal semantic definitions, the PLanCompS project has developed a component-based approach. In this approach, the semantics of a language is defined by translating its constructs (compositionally) to combinations of so-called fundamental constructs, or ‘funcons’. Each funcon is defined using a modular variant of Structural Operational Semantics, and forms a language-independent component that can be reused in definitions of different languages. A substantial library of funcons has been developed and tested in several case studies. Crucially, the definition of each funcon is fixed, and does not need changing when new funcons are added to the library.For specifying component-based semantics, we have designed and implemented a meta-language called CBS. It includes specification of abstract syntax, of its translation to funcons, and of the funcons themselves. Development of CBS specifications is supported by an integrated development environment. The accuracy of a language definition can be tested by executing the specified translation on programs written in the defined language, and then executing the resulting funcon terms using an interpreter generated from the CBS definitions of the funcons. This paper gives an introduction to CBS, illustrates its use, and presents the various tools involved in our implementation of CBS

Prefix orders as a general model of dynamics

In this report we formalize and study the notion of prex order on the executions of general dynamical systems and use basic category theory to show that appropriate structure preserving maps between such orders lead to the well-known notions of bisimulation, renement, product, and union of behavior, without relying on a notion of 'next state'. Thus these notions are generalized to apply to arbitrary dynamical systems, including continuous and hybrid systems

Checking property preservation of refining transformations for model-driven development

In Model-Driven Software Development, a software product is created through iteratively refined modelling. It is crucial that this process preserves certain desirable properties of the initial model. However, checking this is increasingly difficult as the models are increasingly more refined. We propose an incremental model checking technique to determine the preservation of safety and liveness properties in models of concurrent systems with respect to changes applied on individual processes, formalised as transformations of Labelled Transition Systems. The preservation check involves checking bisimilarity between transformed and new behaviour, and never involves reexploring unchanged behaviour. We prove its correctness and demonstrate its applicability

Software engineering : redundancy is key

Software engineers are humans and so they make lots of mistakes. Typically 1 out of 10 to 100 tasks go wrong. The only way to avoid these mistakes is to introduce redundancy in the software engineering process. This article is a plea to consciously introduce several levels of redundancy for each programming task. Depending on the required level of correctness, expressed in a residual error probability (typically 10-3 to 10-10), each programming task must be carried out redundantly 4 to 8 times. This number is hardly influenced by the size of a programming endeavour. Training software engineers does have some effect as non trained software engineers require a double amount of redundant tasks to deliver software of a desired quality. More compact programming, for instance by using domain specific languages, only reduces the number of redundant tasks by a small constant

Incorporating formal techniques into industrial practice

We report about experiences with component-based development supported by formal techniques at Philips Healthcare. The formal Analytical Software Design (ASD) approach of the company Verum has been incorporated into the industrial workflow. The commercial tool ASD:Suite supports both compositional verification and code generation for control components. For other components test-driven development has been used. We discuss the results of these combined techniques in a project which developed the power control service of an interventional X-ray system