A theory of data-intensive software services

We introduce Abstract State Services (AS²s) as an abstraction of data-intensive services that can be made available for use by other systems, e.g. via the web. An AS² combines a hidden database layer with an operation-equipped view layer, and can be anything from a simple function to a full-fledged Web Information System or a Data Warehouse. We adopt the fundamental approach of Abstract State Machines to model AS²s and show that AS²s capture the fundamentals of approaches such as media types, meme media, SOA and web services excluding presentation issues. Then we show how tailored services can be extracted from available AS²s, combined with other AS² components and personalised to user preferences.     

Towards a theory of consistency enforcement

State oriented specifications with invariants occur in almost all formal specification languages. Hence the problem is to prove the consistency of the specified operations with respect to the invariants. Whilst the problem seems to be easily solvable in predicative specifications, it usually requires sophisticated verification efforts, when specifications in the style of Dijkstra's guarded commands as e.g. in the specification language B are used. As an alternative consistency enforcement will be discussed in this paper. The basic idea is to replace inconsistent operations by new consistent ones preserving at the same time the intention of the old one. More precisely, this can be formalized by consistent spezializations, where specialization is a specific partial order on operations defined via predicate transformers. It will be shown that greatest consistent specializations (GCSs) always exist and are compatible with conjunctions of invariants. Then under certain mild restrictions the general construction of such GCSs is possible. Precisely, given the GCSs of simple basic assignments the GCS of a complex operation results from replacing involved assignments by their GCSs and the investigation of a guard. In general, GCS construction can be embedded in refinement calculi and therefore strengthens the systematic development of correct programs. Received: 28 April 1994 / 5 November 1998     

Customising Web Information Systems According to User Preferences

Web Information Systems have to serve a variety of users with very diverse preferences regarding content, functionality and presentation. We first investigate the customisation of functionality at a high-level of abstraction, where possible action sequences are represented by an algebraic expression called plot, and user preferences give rise to equations. We show that the problem can be solved by applying conditional term rewriting on the basis of Kleene algebras with tests. By exploiting the idea of weakest preconditions such expressions can be represented by formal power series with coefficients in a Boolean algebra. This gives rise to a sufficient condition for termination based on well-founded orders on such power series. As confluence cannot be guaranteed, we propose critical pair completion to be used in order to enforce the desirable Church-Rosser property. In a second step we parametrise the actions and replace the Boolean conditions by first-order formulae. We show that still term rewriting can be applied, but termination and Church Rosser property become problems that will require manual interaction, in particular, as preference rules will make use of the parameters. On the other hand the presence of first-order conditions can be used to extend the customisation to the content.     

A Bayesian approach to information fusion for evaluating the measurement uncertainty

The Bayesian approach to uncertainty evaluation is a classical example of the fusion of information from different sources. Basically, it is founded on both the knowledge about the measurement process and the influencing quantities and parameters. The knowledge about the measurement process is primarily represented by the so-called model equation, which forms the basic relationship for the fusion of all involved quantities. The knowledge about the influencing quantities and parameters is expressed by their degree of belief, i.e. appropriate probability density functions that usually are obtained by utilizing the principle of maximum information entropy and the Bayes theorem. Practically, the Bayesian approach to uncertainty evaluation is put into effect by employing numerical integration techniques, preferably Monte-Carlo methods. Compared to the ISO-GUM procedure, the Bayesian approach does not have any restrictions with respect to nonlinearities and calculation of confidence intervals.     

Knowledge-aware identity services

The identification problem is concerned with the question whether two objects in an application refer to the same real-world entity. In this paper, the identification problem is investigated from a knowledge modelling point of view. We develop a framework of establishing knowledge-aware identity services by abstracting identity knowledge into an additional identity layer. The knowledge model in the identity service layer provides a capability for combining declarative formulae with concrete data and thus allows us to capture domain-specific identity knowledge at flexible levels of abstraction. By adding validation constraints to the identity service, we are also able to reason about inconsistency of identity knowledge. In doing so, the accuracy of identity knowledge can be improved over time, especially when utilising identity services provided by different communities in a service-oriented architecture. Our experimental study shows the effectiveness of the proposed knowledge modelling approach and the effects of domain-specific identity knowledge on data quality control.     

Information systems design: through adaptivity to ubiquity

In a globalised economy the accessibility of services becomes increasingly important for businesses. This has led to a demand that information systems should be ubiquitous in the sense that they are available to all users under all circumstances, everywhere and at all times, and independent of the access devices and channels used. The authors believe the key to meeting that demand is existence of an omnipresent media of interaction and existence of information systems that within that media adapt themselves to context parameters at run-time. The World Wide Web is considered as that omnipresent media. Thus, the task is left to design adaptive information systems in a way that avoids unnecessary replication. In this article it will be shown how context parameters can be utilised to enable system adaptivity. The latter is supposed to increase usability and targets the quality of use, the content, and the functionality. We propose using an algebraic approach that aids in providing the leanest appropriate interface via user typing and story boarding. Our approach furthermore limits the content delivered to a user to the amount that can be dealt with in a usage scenario. The latter is based on defining hyphenation points within the content.

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Systematic Maintenance of Corporate Experience Repositories

Experience-based continuous learning is essential for improving products, processes, and technologies in emerging as well as established areas of business and engineering science. This can be facilitated by case-based organizational learning through capturing relevant experience in the form of cases for reuse in a corporate experience repository. For obvious reasons, learning from experience needs to be a permanent endeavor. Thus an organization has to handle a "continuous stream of experience." Consequently, such an experience repository requires maintenance. This should not simply happen ad hoc but in a systematic manner. To make competent decisions about maintenance, the experience base and its usage have to be analyzed (i.e., evaluated). To improve maintenance itself, it is necessary to learn about it. For this purpose, we identify the relevant tasks for maintaining an experience repository and the responsibilities of the roles involved. Maintenance addresses not only the actual experience in the form of cases but also the conceptual model and the methods, techniques, and tools that are used for filling and updating the experience repository. To support the roles involved in the maintenance tasks, we provide a flexible, practical maintenance and evaluation framework. This framework provides guidance for the roles. The framework can be combined with other approaches from artificial intelligence, knowledge engineering, and software engineering at different levels of detail. For the practical application of the framework, we describe an integrated technical solution for a corporate experience repository that is maintained using our framework. Furthermore, we discuss the empirical validation of the framework and its implementation.