Simon Foster

A compositional operational semantics for OWL-S

Software composition via workflow specifications has received a great deal of attention recently. One reason is the high degree of fit with the encapsulation of software modules in service-oriented fashion. In the Industry, existing workflow languages have been merged to form WS-BPEL, the Business Process Execution Language for Web Services. In the Research community OWL-S, a ontology for web services, has been submitted for standardisation alongside OWL, the Web Ontology Language in which it is expressed. The OWL-S Process Model is based on an abstraction of the common features of industrial workflow languages. On the one hand, WS-BPEL has only informal semantics; on the other, the type of semantics given to ontology-based work tends to be structural rather than computationally oriented. As a result the semantics developed for DAML-S, which led to OWL-S, are still deficient in some regards. In this paper we shall survey the existing semantics and introduce a novel semantics for the latest version of OWL-S that is focussed on the principle of compositionality, so far not tackled.

Isabelle/UTP : A Mechanised Theory Engineering Framework

We introduce Isabelle/UTP, a novel mechanisation of Hoare and He’s Unifying Theories of Programming (UTP) in Isabelle/HOL. UTP is a framework for the study, formalisation, and unification of formal semantics. Our contributions are, firstly, a deep semantic model of UTP’s alphabetised predicates, supporting meta-logical reasoning that is parametric in the underlying notions of values and types. Secondly, integration of host-logic type checking that subsumes the need for typing proof obligations in the object-language. Thirdly, proof tactics that transfer results from well-supported mathematical structures in Isabelle to proofs about UTP theories. Additionally, our work provides novel insights towards reconciliation of shallow and deep language embeddings.

COMPASS tool vision for a system of systems Collaborative Development Environment

It would be useful to have a tool platform that supports systematic engineering of Systems of Systems, especially focused on the case where multiple parties are collaborating on the development. We attempt to provide a vision for a tool that allows collaboration on models developed jointly and that can be systematically analysed. The focus is on the challenges that make this kind of tool - a Collaborative Development Environment- different from a traditional Integrated Development Environment. Finally the paper describes the plans of the COMPASS project to address these challenges.

Towards a UTP Semantics for Modelica

We describe our work on a UTP semantics for the dynamic systems modelling language Modelica. This is a language for modelling a system’s continuous behaviour using a combination of differential-algebraic equations and an event-handling system. We develop a novel UTP theory of hybrid relations, inspired by Hybrid CSP and Duration Calculus, that is purely relational and provides uniform handling of continuous and discrete variables. This theory is mechanised in our Isabelle implementation of the UTP, Isabelle/UTP, with which we verify some algebraic properties. Finally, we show how a subset of Modelica models can be given semantics using our theory. When combined with the wealth of existing UTP theories for discrete system modelling, our work enables a sound approach to heterogeneous semantics for Cyber-Physical systems by leveraging the theory linking facilities of the UTP.

Unifying Theories of Programming in Isabelle

This is a tutorial introduction to the two most basic theories in Hoare & Hes Unifying Theories of Programming and their mechanisation in the Isabelle interactive theorem prover. We describe the theories of relations and of designs pre-postcondition pairs, interspersed with their formalisation in Isabelle and example mechanised proofs.

Integrating an automated theorem prover into agda

Agda is a dependently typed functional programming language and a proof assistant in which developing programs and proving their correctness is one activity. We show how this process can be enhanced by integrating external automated theorem provers, provide a prototypical integration of the equational theorem prover Waldmeister, and give examples of how this proof automation works in practice.

Unifying Heterogeneous State-Spaces with Lenses

Most verification approaches embed a model of program state into their semantic treatment. Though a variety of heterogeneous state-space models exists, they all possess common theoretical properties one would like to capture abstractly, such as the common algebraic laws of programming. In this paper, we propose lenses as a universal state-space modelling solution. Lenses provide an abstract interface for manipulating data types through spatially-separated views. We define a lens algebra that enables their composition and comparison, and apply it to formally model variables and alphabets in Hoare and He’s Unifying Theories of Programming (UTP). The combination of lenses and relational algebra gives rise to a model for UTP in which its fundamental laws can be verified. Moreover, we illustrate how lenses can be used to model more complex state notions such as memory stores and parallel states. We provide a mechanisation in Isabelle/HOL that validates our theory, and facilitates its use in program verification.

Automated analysis of regular algebra

Regular algebras axiomatise the equational theory of regular expressions. We use Isabelle/HOLs automated theorem provers and counterexample generators to study the regular algebras of Boffa, Conway, Kozen and Salomaa, formalise their soundness and completeness (relative to a deep result by Krob) and engineer their hierarchy. Proofs range from fully automatic axiomatic and inductive calculations to integrated higher-order reasoning with numbers, sets and monoid submorphisms. In combination with Isabelles simplifiers and structuring mechanisms, automated deduction provides powerful support to the working mathematician beyond first-order reasoning.

Towards Semantically Integrated Models and Tools for Cyber-Physical Systems Design

We describe an approach to the model-based engineering of embedded and cyber-physical systems, based on the semantic integration of diverse discipline-specific notations and tools. Using the example of a small unmanned aerial vehicle, we explain the need for multiple notations and collaborative modelling. Learning from experience with binary co-modelling based on a bespoke operational semantics, we describe current work delivering an extended approach that enables integration of multiple models and tools in a consistent tool chain, founded on an extensible semantic framework exploiting the Unifying Theories of Programming.

An Approach for Managing Semantic Heterogeneity in Systems of Systems Engineering

Semantic heterogeneity is a significant challenge to integration in Systems of Systems Engineering (SoSE) due the large variety of languages, domains and tools which are used in their construction. In this paper we envision a strategy for managing this heterogeneity by decomposing domain specific languages into their “building block” theories which can be independently analysed, and used as a basis for linking with similar notations. This provides a systematic approach to building a tool-chain which integrates the different theories, methods and tools used in SoSE. Our approach has been piloted on the development of theories enabling machine-supported analysis of SysML models of SoSs. We conclude that the approach has further potential and identify lines of future research, notably in techniques for handling mixed discrete and continuous behaviour, timebands, mobility and model integration in SoSE.