A Logic-Based Formalization for Component Specification

We consider a component-based approach to modelling complex systems using UML. We describe how component concepts at a specification level (interfaces, components, architectures) can be formalized in a uniform way using a distributed logical framework. In the logic MDTL, each component has associated to it a local logic consisting of a home logic and a communication logic. Component con-tracts are captured by formulae in MDTL. In particular, a clear distinction between usage and realization contracts is made: the former is captured as formulae in the home logic of the interface specification, whilst the latter is ex-pressed by formulae in the communication logic of the com-ponent specification. Moreover, we are investigating an ex-tension of the framework for expressing dependability re-quirements.

Foundations of a Module Concept for Distributed Object Systems

This thesis provides a logical and mathematical foundation for object-oriented specification languages with a further modularisation unit between the system and object classes. The unit is denoted object-oriented module, or module for short, and initially described in an informal way. Modules offer a better approach to reusability and provide better structuring of large, complex and distributed systems. In our approach, systems..

Using a Modular Distributed Temporal Logic for In-the-large Object Specification

Our general goal is to provide a semantic foundation for in-the-large specification of distributed information systems. We use Troll, an object-oriented formal language, for system specification. Our claim is that objects are not enough as a modularisation unit when it comes to deal with very large systems. An intermediary concept between the system and the objects is needed for allowing reusability of specifications and provide a clearer system structure. Enriching Troll with a module concept enforces us to develop new theoretical constructs ensuring an appropriate underpinning of the language. A modular distributed temporal logic Mdtl has been developed which describes the dynamic aspects of modular systems. The main features of the logic are its own modularity, the ability to express inter-module (a)synchronous communication and intra-module concurrency. It also seems promising to support module refinement. Mdtl is based on n-agent logics and interpreted over labelled prime event struct..

Putting Synchronous and Asynchronous Object Modules together: an Event-Based Model for Concurrent Composition

In this paper we show how by means of a categorical framework we can compose systems of concurrent object modules satisfying some interaction rules given by a specification. Module interaction can be either synchronous or asynchronous and both cases are considered separately. The behaviour of object modules is modelled by labelled prime event structures. The category of labelled prime event structures has (co)products. A product in the category of labelled prime event structures is given accordingly to Winskel and Nielsen but denotes parallel composition in a sense that does not have much practical interest. For synchronously communicating modules, by applying to the product a restriction on the allowed life cycles by means of the categorical concept of a functor induced by a co bration and a morphism on labels, we achieve the desired joint behaviour. A way to model asynchronous composition of modules is to construct a coproduct and extend it by their interaction rules. At the end of ..

A Categorical Hiding Mechanism for Concurrent Object Systems

We present a categorical mechanism to model interfaces in concurrent modular object systems. The behaviour of objects is modelled by sequential labelled prime event structures. Objects can be grouped into modules denoting system parts which are modelled by labelled event structures. The behaviour of systems is achieved from its interconnected modules by combining compositional and hiding mechanisms. A forgetful functor from the category of labelled prime event structures into the category of labels is introduced and proved to be a cofibration. We define two kinds of hiding morphisms on labels: total and partial. The total induces with the cofibration a functor that is useful for hiding actions, while the partial allows us to hide entire objects and thus obtain module interfaces. Moreover, an interesting application of the latter shows how to model asynchronous communication via synchronous one

Decomposing interactions

In UML 2.0 sequence diagrams have been considerably extended and are now fundamentally better structured. Interactions in sequence diagrams can be structured using so-called interaction fragments, including alt (alternative behaviour), par (parallel behaviour), neg (forbidden behaviour), assert (mandatory behaviour) and ref (reference another diagram). The operator ref in particular greatly improves the way diagrams can be decomposed. In previous work we have given a semantics to a subset of sequence diagrams using labelled event structures, a true-concurrent model that naturally captures alternative and parallel behaviour. In this paper, we expand that work to address refinement and show how to obtain a refined model by means of a powerful categorical construction over two categories of labelled event structures. The underlying motivation for this work is reasoning and verification of complex scenario-based inter-object behavioural models. We conclude the paper with a discussion on future work.</p

Limits in Modelling Evolving Computer-based Systems

This paper explores the limitations of one technique for modelling computer-based systems with evolving requirements. A case study is introduced which highlights the importance of taking a multi-perspective on dependable computer-based systems. This should be reflected in the modelling technique. Such considerations motivate our ongoing research agenda