M. Howard Williams

Dimensions of Active Behaviour

This paper introduces a number of dimensions of active rule system behaviour which can be used both to highlight differences between proposals for active rule systems, and to identify the requirements of different applications. These dimensions relate to the structure, execution model and management of active rules, and enable the concise expression of what facilities a system supports and what features an application requires.

Rules in Database Systems

Objects are collected into an object base because of a presumed need for cooperation among them. In classical object bases the cooperation is based on synchronous, preplanned message exchange. Many of the modern application scenarios such as industrial and office automation with their high volume of concurrent, interleaved, and iterative actions defy preplanning and require the support of a highly dynamic relationships among the objects. It is the central hypothesis of this paper that the dynamics within such an object base is best covered by the metaphor of communications protocol taken from the telecommunications world. Active objects with their individual threads-of-control establish temporary communication links via a medium which we refer to as activities. Active objects and activity cooperate via a protocol. The main benefit of such an approach is a clear separation of object-local and cooperative aspects of a common task. The paper augments an existing strongly-typed object-oriented language by active objects with an underlying event processing model based on incoming messages, and by activities with an event processing model based on interfering messages. The interplay between them is demonstrated by an implementation of the classical Two-Phase-Commit protocol as a generic example for negotiations among objects.

Design and implementation of ROCK & ROLL: a deductive object-oriented database system

This paper presents an approach to the development of a deductive object-oriented database system, describing the key design decisions and their consequences for implementation. The approach is novel, in that it integrates an object-oriented database system manipulated using an imperative programming language (ROCK) with a logic language for expressing queries and methods (ROLL). The integration is made seamless by deriving both the imperative and logic languages from a single formally defined data model, thereby avoiding impedance mismatches when they are integrated.

A logic-based integration of active and deductive databases

A logic-based approach to the specification of active database functionality is presented which not only endows active databases with a well-defined and well-understood formal semantics, but also tightly integrates them with deductive databases. The problem of endowing deductive databases with rule-based active behaviour has been addressed in different ways. Typical approaches include accounting for active behaviour by extending the operational semantics of deductive databases, or, conversely, accounting for deductive capabilities by constraining the operational semantics of active databases. The main contribution of the paper is an alternative approach in which a class of active databases is defined whose operational semantics is naturally integrated with the operational semantics of deductive databases without either of them strictly subsuming the other. The approach is demonstrated via the formalization of the syntax and semantics of an active-rule language that can be smoothly incorporated into existing deductive databases, due to the fact that the standard formalization of deductive databases is reused, rather than altered or extended. One distinctive feature of the paper is its use of ahistory, as defined in the Kowalski-Sergot event-calculus, to define event occurrences, database states and actions on these. This has proved to be a suitable foundation for a comprehensive logical account of the concept set underpinning active databases. The paper thus contributes a logical perspective to the ongoing task of developing a formal theory of active databases.

Pharmaceutical applications of variable-angle synchronous scanning fluorescence spectroscopy

Abstract The development of variable-angle synchronous scanning (v.a.s.s.) in fluorescence spectrometry is reported, based on a computer-aided spectrofluorimeter. The technique permits a linear path to be scanned at any preselected angle through the emission-excitation matrix defined by (Iem, λem, λex), by effectively scanning the emission and the excitation monochromators at different speeds under computer control. When applied to pharmaceutical dosage forms, v.a.s.s. gave good selectivity for chlorpromazine in the presence of its principal degradation product, chlorpromazine sulphoxide, and for oxytetracycline in the presence of the additives vitamin C, thiamine, nicotinamide and riboflavin. Good calibration linearity, precision and recovery were observed for both principal drug components. The angle of the scan trajectory can also be varied continuously through the emission-excitation matrix, to describe any desired path under computer control. This novel technique of non-linear v.a.s.s. can provide an improved method for generating diagnostic profiles of drugs, degradation products and metabolites.

Formal Specification of Active Database Functionality: A Survey

This paper reviews research on the formal specification of active behaviour, indicating both what has been done in this area, and how. The scope of different approaches is compared within a common framework, which reveals that although many aspects of active behaviour have been described formally, no single proposal covers all phenomena associated with active database systems.

A Model for Query Decomposition and Answer Construction inHeterogeneous Distributed Database Systems

The problem of retrieving information from a collection of heterogeneous distributed databases has attracted a number of solutions. However, the task of integrating established database systems is complicated not only by the differences between the database systems themselves, but also by the differences in structure and semantics of the information contained within them. The problem is exacerbated when one needs to provide access to such a system for naive end-users.This paper is concerned with a Knowledge-Based Systems approach to solving this problem for clearly bounded situations, in which both the domain and the types of query are constrained. At the user interface, dialogue is conducted in terms of concepts with which the user is familiar, and these are then mapped into appropriate database queries. To achieve this a model for query decomposition and answer construction has been used. This model is based around the development of an Intensional Structure containing information necessary for the recapture of semantic information lost in the query decomposition process and required in the answer construction process. The model has been successfully implemented in combination with an embedded KBS, within a five-layer representation model.

Deduction and Deductive Databases for Geographic Data Handling

The representation of complex spatial domains in conventional databases suffers from fragmented representation of object structure, lack of instance-level spatial relationships, and the generation of large combinatoric search spaces in query analysis. The deductive capabilities provided by a deductive database offer some assistance in solving these problems, in particular by enabling spatial reasoning to be performed by a Geographic Information System (GIS). Deduction in the database is used to support the natural representation of complex spatial object structures in single and multi-layered Geographic DataBases (GDB), inference of implicit spatial relationships, and the manipulation of multiple resolution spatial representations. In addition, deductive capabilities are shown to be essential for automatic data input and update in a GDB. Coupled with appropriate structural representation, spatial reasoning is an important tool for the realization of an effective GDB.

Geographic Data Handling in a Deductive Object-Oriented Database

This paper describes how a deductive object-oriented database (DOOD) can be used to support the storage and management of data which is typical of that found in geographic information systems (GIS). This is done with two aims in mind: to illustrate how a combination of deductive and object-oriented facilities can be applied effectively in an advanced application, thereby motivating the development of DOOD systems; and to show how geographic database systems stand to gain from the utilisation of advanced data modelling and inference facilities as supported by a DOOD. The paper describes the DOOD system which has been used for prototyping a range of geographic concepts, presents a framework for the structural organisation of GIS data using an object-oriented data model, and shows how a logic query language can be used within this structural framework to perform a range of analyses.

Context-Aware dynamic personalised service re-composition in a pervasive service environment

A pervasive environment needs to take account of a user’s context and preferences in determining which services to provide to the user. Moreover, one of the important features of a pervasive service environment is its dynamic nature, with the ability to adapt services as the context of a user changes, e.g. as he/she moves around. This paper describes how these requirement changes can be sufficiently accounted for by using a personalisation component to ‘decide’ what a user needs, and a composition component to continuously monitor services and the changes associated with them. The paper presents how services can be recomposed dynamically if the changes in context require it. This approach has been incorporated into a platform to support pervasive services. The service composition process used is described, and the way in which personalisation is incorporated into this process is shown. Finally the paper provides a brief account of two prototypes built as a proof of concept for these ideas.