Reusability in software engineering

This paper surveys recent work concerning reusability in software engineering. The current directions in software reusability are discussed, and the two major approaches of reusable building blocks and reusable patterns studied. An extensive bibliography, parts of which are annotated, is included

Graph models for reachability analysis of concurrent programs

Reachability analysis is an attractive technique for analysis of concurrent programs because it is simple and relatively straightforward to automate, and can be used in conjunction with model-checking procedures to check for application-specific as well as general properties. Several techniques have been proposed differing mainly on the model used; some of these propose the use of flowgraph based models, some others of Petri nets.This paper addresses the question: What essential difference does it make, if any, what sort of finite-state model we extract from program texts for purposes of reachability analysis? How do they differ in expressive power, decision power, or accuracy? Since each is intended to model synchronization structure while abstracting away other features, one would expect them to be roughly equivalent.We confirm that there is no essential semantic difference between the most well known models proposed in the literature by providing algorithms for translation among these models. This implies that the choice of model rests on other factors, including convenience and efficiency.Since combinatorial explosion is the primary impediment to application of reachability analysis, a particular concern in choosing a model is facilitating divide-and-conquer analysis of large programs. Recently, much interest in finite-state verification systems has centered on algebraic theories of concurrency. Yeh and Young have exploited algebraic structure to decompose reachability analysis based on a flowgraph model. The semantic equivalence of graph and Petri net based models suggests that one ought to be able to apply a similar strategy for decomposing Petri nets. We show this is indeed possible through application of category theory

Tasking Event-B: An Extension to Event-B for Generating Concurrent Code

The Event-B method is a formal approach for modelling systems in safety-, and business-critical, domains. Initially, system specification takes place at a high level of abstraction; detail is added in refinement steps as the development proceeds toward implementation. Our aim has been to develop a novel approach for generating code, for concurrent programs, from Event-B. We formulated the approach so that it integrates well with the existing Event-B methodology and tools. In this paper we introduce a tasking extension for Event-B, with Tasking and Shared Machines. We make use of refinement, decomposition, and the extension, to structure projects for code generation for multitasking implementations. During the modelling phase decomposition is performed; decomposition reduces modelling complexity and makes proof more tractable. The decomposed models are then extended with sufficient information to enable generation of code. A task body describes a task’s behaviour, mainly using imperative, programming-like constructs. Task priority and life-cycle (periodic, triggered, etc.) are also specified, but timing aspects are not modelled formally. We provide tool support in order to validate the practical aspects of the approach

Boson Condensation in Topologically Ordered Quantum Liquids

Boson condensation in topological quantum field theories (TQFT) has been previously investigated through the formalism of Frobenius algebras and the use of vertex lifting coefficients. While general, this formalism is physically opaque and computationally arduous: analyses of TQFT condensation are practically performed on a case by case basis and for very simple theories only, mostly not using the Frobenius algebra formalism. In this paper we provide a new way of treating boson condensation that is computationally efficient. With a minimal set of physical assumptions, such as commutativity of lifting and the definition of confined particles, we can prove a number of theorems linking Boson condensation in TQFT with chiral algebra extensions, and with the factorization of completely positive matrices over the nonnegative integers. We present numerically efficient ways of obtaining a condensed theory fusion algebra and S matrices; and we then use our formalism to prove several theorems for the S and T matrices of simple current condensation and of theories which upon condensation result in a low number of confined particles. We also show that our formalism easily reproduces results existent in the mathematical literature such as the noncondensability of 5 and 10 layers of the Fibonacci TQFT.Comment: 29 page

A VISUAL DESIGN METHOD AND ITS APPLICATION TO HIGH RELIABILITY HYPERMEDIA SYSTEMS

This work addresses the problem of the production of hypermedia documentation for applications that require high reliability, particularly technical documentation in safety critical industries. One requirement of this application area is for the availability of a task-based organisation, which can guide and monitor such activities as maintenance and repair. In safety critical applications there must be some guarantee that such sequences are correctly presented. Conventional structuring and design methods for hypermedia systems do not allow such guarantees to be made. A formal design method that is based on a process algebra is proposed as a solution to this problem. Design methods of this kind need to be accessible to information designers. This is achieved by use of a technique already familiar to them: the storyboard. By development of a storyboard notation that is syntactically equivalent to a process algebra a bridge is made between information design and computer science, allowing formal analysis and refinement of the specification drafted by information designers. Process algebras produce imperative structures that do not map easily into the declarative formats used for some hypermedia systems, but can be translated into concurrent programs. This translation process, into a language developed by the author, called ClassiC, is illustrated and the properties that make ClassiC a suitable implementation target discussed. Other possible implementation targets are evaluated, and a comparative illustration given of translation into another likely target, Java