17770007
Encoding Object-Z in Isabelle/HOL
In this paper, we present a formalisation of the reference semantics of Object-Z in the higher-order logic (HOL) instantiation of the generic theorem prover Isabelle, Isabelle/HOL. This formalisation has the effect of both clarifying the semantics and providing the basis for a theorem prover for Object-Z. The work builds on an earlier encoding of a value semantics for object-oriented Z in Isabelle/HOL and a denotational semantics of Object-Z based on separating the internal and external effects of class methods.
8767817
Incremental Development of Real-Time Requirements: The Light Control Case Study
System requirements frequently change while the system is still under development. Usually this means going back and revising the requirements specification and redoing those development steps already completed. In this article we show how formal requirements can be allowed to evolve while system development is in progress, without the need for costly redevelopment. This is done via a formalism which allows requirements engineering steps to be interleaved with formal development steps in a manageable way. The approach is demonstrated by a significant case study, the Light Control System.
671422
Specifying Mode Requirements of Embedded Systems
This paper presents a formal notation for specifying requirements of embedded systems which exhibit continuous, real-time behaviour and move through various modes under digital control. It does this by extending an existing formal notation supporting continuous, real-time behaviour with an explicit concept of modes. The resulting notation avoids the subtleties which would otherwise arise when specifying mode-related requirements. It is therefore ideal as a means of specifying and communicating requirements of embedded systems.
52867012
An Object-Oriented Development Framework for Z
This paper presents a framework for developing Z specifications in an object-oriented style. Within the framework, object-oriented concepts and design strategies are captured by the application of development operators. The framework also records the history of operator application enabling “classes” to be identified and, hence, the possibility of modular verification and refinement.
18518522
A Development Framework for Object-Oriented Specification and Refinement
This paper presents a language-independent framework for developing formal speciications in an intuitively object-oriented style. Within the framework, object-oriented concepts and design strategies are captured by the application of development operators. The operators, by eeec-tively hiding the technical details of how object-oriented concepts are captured in a given speci-cation language, allow the speciier to develop speciications in an intuitively object-oriented fashion. They also present a exible approach to object-oriented speciication as libraries of operators can be deened allowing many diierent dee-nitions of object-oriented features to be available. This enables a close mapping to be achieved between the speciication and the implementation in the chosen object-oriented programming language. The framework also records the history of operator application enabling \classes" and \modules" to be identiied in the resulting spec-iications and, hence, the possibility of modular veriication and reenement.
594379
Extending W for Object-Z
This paper presents a logic for Object-Z which extends W, the logic for Z adopted as the basis of the deductive system in the Z Base Standard. The logic provides a basis on which tool support for reasoning about Object-Z specifications can be developed. It also formalises the intended meaning of Object-Z constructs and hence provides an abstract, axiomatic semantics of the language.
42279258
A Unified Paradigm for Parallel Genetic Algorithms
Genetic Algorithms contain natural parallelism. There are two main approaches in parallelising GAs. The first one is parallelising individual functional components of a standard, sequential GA. The only difference with the sequential GA is in the computation speed. The second approach more closely resembles the real life simultaneous evolution of species, which is the central theme in GAs. Algorithms following this approach are still referred to as GAs but are different from Holland's standard GA. For these algorithms it is not the improvement in computation speed that is the driving factor, but the efficiency with which they search a given solution space. We describe a number of the most common parallel GA methods found in the literature and mention practical issues concerning their implementation in a Transputer based system. We go on to introduce the Unified Parallel GA system, based on our GA toolkit, GAmeter, which allows the user to select one or more of the GA methods described, by setting various parameters. Finally we present results for the Steiner tree Problem in Graphs (SPG).
206854015
Fitness Distance Correlation and Ridge Functions
Fitness Distance Correlation has been proposed as a measure of function optimization difficulty. This paper describes a class of functions, named the Ridge Functions which, according to the measure, should be highly misleading. However, all functions tested were optimized easily by both a GA and a simple hill climbing algorithm. Scatter graph analysis of Ridge functions gave little guidance due to the large number of functions with an identical scatter graph, the majority of which are not in the class of Ridge functions and are not simple to optimize.
14865714
Breast Composition Measurements Using Retrospective Standard Mammogram Form (SMF)
The standard mammogram form (SMF) representation of an x-ray mammogram is a standardized, quantitative representation of the breast from which the volume of non-fat tissue and breast density can be easily estimated, both of which are of significant interest in determining breast cancer risk. Previous theoretical analysis of SMF had suggested that a complete and substantial set of calibration data (such as mAs and kVp) would be needed to generate realistic breast composition measures and yet there are many interesting trials that have retrospectively collected images with no calibration data. The main contribution of this paper is to revisit our previous theoretical analysis of SMF with respect to errors in the calibration data and to show how and why that theoretical analysis did not match the results from the practical implementations of SMF. In particular, we show how by estimating breast thickness for every image we are, effectively, compensating for any errors in the calibration data. To illustrate our findings, the current implementation of SMF (version 2.2beta) was run over 4028 digitized film-screen mammograms taken from six sites over the years 1988-2002 with and without using the known calibration data. Results show that the SMF implementation running without any calibration data at all generates results which display a strong relationship with when running with a complete set of calibration data, and, most importantly, to an expert's visual assessment of breast composition using established techniques. SMF shows considerable promise in being of major use in large epidemiological studies related to breast cancer which require the automated analysis of large numbers of films from many years previously where little or no calibration data is available.