Efficient methods of processing unanticipated queries are a crucial prerequisite for the success of generalized database management systems. A wide variety of approaches to improve the performance of query evaluation algorithms have been proposed: logic-based and semantic transformations, fast implementations of basic operations, and combinatorial or heuristic algorithms for generating alternative access plans and choosing among them. These methods are presented in the framework of a general query evaluation procedure using the relational calculus representation of queries. In addition, nonstandard query optimization issues such as higher level query evaluation, query optimization in distributed databases, and use of database machines are addressed. The focus, however, is on query optimization in centralized database systems.

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Query Optimization in Database Systems

Current workflow management systems still lack support for dynamic and automatic workflow adaptations. However, this functionality is a major requirement for next-generation workflow systems to provide sufficient flexibility to cope with unexpected failure events. We present the concepts and implementation of AGENTWORK, a workflow management system supporting automated workflow adaptations in a comprehensive way. A rule-based approach is followed to specify exceptions and necessary workflow adaptations. AGENTWORK uses temporal estimates to determine which remaining parts of running workflows are affected by an exception and is able to predictively perform suitable adaptations. This helps to ensure that necessary adaptations are performed in time with minimal user interaction which is especially valuable in complex applications such as for medical treatments.

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AGENT WORK: a workflow system supporting rule-based workflow adaptation

Using traditional and emerging access control approaches to develop secure applications for the Web.

Security models for web-based applications

Workflow management systems, a relatively recent technology, are designed to make work more efficient, integrate heterogeneous application systems, and support interorganizational processes in electronic commerce applications. In this paper, we introduce the field of workflow automation, the subject of this special issue of Information Systems Frontiers. In the first part of the paper, we provide basic definitions and frameworks to aid understanding of workflow management technologies. In the remainder of the paper, we discuss technical and management research opportunities in this field and discuss the other contributions to the special issue.

Workflow Automation: Overview and Research Issues

The purpose of this paper is to explore some semantic problems related to the use of linguistic ontologies in information systems, and to suggest some organizing principles aimed to solve such problems. The taxonomic structure of current ontologies is unfortunately quite complicated and hard to understand, especially for what concerns the upper levels. I will focus here on the problem of ISA overloading, which I believe is the main responsible of these difficulties. To this purpose, I will carefully analyze the ontological nature of the categories used in current upper-level structures, considering the necessity of splitting them according to more subtle distinctions or the opportunity of excluding them because of their limited organizational role.

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Some Ontological Principles for Designing Upper Level Lexical Resources

Question-answering systems must often keep certain information secret. This can be accomplished, for example, by sometimes refusing to answer a query. Here the danger of revealing a secret by refusing to answer a query is investigated. First several criteria that can be used to decide whether or not to answer a query are developed. Then it is shown which of these criteria are safe if the questioner knows nothing at all about what is kept secret. Furthermore, it is proved that one of these criteria is safe even if the user of the system knows which information is to be kept secret.

Answering queries without revealing secrets

Workflow Management (WFM) Systems automate traditional processes where information flows between individuals. WFM systems have two major implications for security. Firstly, since the description of a workflow process explicitly states when which function is to be performed by whom, security specifications may be automatically derived from such descriptions. Secondly, the derived security specifications have to be enforced.

The paper considers the issues that need to be addressed by a secure workflow system. In particular it addresses the requirement that security for workflow systems need to be specified at the workflow level, and not at the level of the underlying components, such as the database or networks. One reason why it is necessary to consider security at this level is the dynamic nature of workflow systems, with access restrictions depending on the state of the workflow process. In addition, workflow systems may handle many instances of a given workflow specification and needs to be able to protect the instances according to the requirements posed by each.

The intention of this paper is to provide an orderly framework for these concepts and to discuss a more generalized implementation architecture which can be based on existing technologies of the Web and Object-oriented systems. The framework is based on three levelsc Modelling, Specification and Implementations each level refines the concepts of the level above it.

Modelling is illustrated by using a notion of Alter-Egos and a workflow modelling tool known as COLOR-X. How these and related concepts may be formally specified are considered in the second part of the paper. The specification is based on the formal language Z. The implementation section considers protocols, standards and architectures that may be used to realize such a secure workflow system. Since the implementation does not use any specific system but only very general components, it can be realized on various platforms.

Modelling, specifying and implementing workflow security in Cyberspace

As conceptual models reflect people's perception of real-world phenomena, they are closely tied to the way people describe and talk about these phenomena in natural language. The models, used for developing database and information systems and for presenting or explaining databases, usually include linguistic notions to help interpret their contents. In this paper, we show how linguistic knowledge from a semantically based lexicon can be used to check the quality of conceptual models. The check is a natural extension of traditional verification checks, and its purpose is to ensure that words and phrases included in the models are used in a linguistically meaningful way. Linguistic expressions must be of the correct type, and the relationships between expressions in the model must be acceptable with respect to the semantic constraints indicated in the lexicon.

Verification of Conceptual Models based on Linguistic Knowledge.

This paper introduces a way of modeling the dynamic aspects of an Information and Communication System in which all the occurring events are listed and ordered in time. These graphical Event Models are based on formal (logical) specifications. Event Models are very close to the specifications in the informal requirements document, which describes the Universe of Discourse. By means of the underlying formal specifications Natural Language sentences are generated automatically, in order to give some feedback to the designer and user. By combining this feedback feature and the power of the logical foundation, the Event Models can be verified and validated. We will also present an algorithm and its implementation to generate State Transition Diagrams from Event Models automatically. This is especially useful in our environment in which programming code-generation is the key objective.

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COLOR-X: Linguistically-based Event Modeling: A General Approach to Dynamic Modeling

This paper discusses some high-level language programming constructs that can be used to manipulate the relations of a relational database system efficiently. Three different constructs are described: (1) tuple identifiers that directly reference tuples of a relation; (2) cursors that may iterate over the tuples of a relation; and (3) markings, a form of temporary relation consisting of a set of tuple identifiers. In each case, attention is given to syntactic, semantic, and implementation considerations.The use of these features is first presented within the context of the programming language PLAIN, and it is then shown how these features could be used more generally to provide database manipulation capabilities in a high-level programming language. Consideration is also given to issues of programming methodology, with an important goal being the achievement of a balance between the enforcement of good programming practices and the ability to write efficient programs.

Reind P. van de Riet

Papers

Answering queries without revealing secrets

Modelling, specifying and implementing workflow security in Cyberspace

Verification of Conceptual Models based on Linguistic Knowledge.

COLOR-X: Linguistically-based Event Modeling: A General Approach to Dynamic Modeling

High-level programming features for improving the efficiency of a relational database system