Paul Johannesson
PhD thesis
Abstract
Decentralized information systems are becoming increasingly tant as a result of organizational demands and as a consequence of technical advances in computer networking. In most approaches to decentralized information systems design, e.g., distributed databases, it has been assumed that the system is viewed by the user as a single logical system described by a global schema, whtrally maintained. Systems based on these assumptions could, in many cases, become too rigid. A looser form of association could then be preferable. This would consist of independent, autonomous infortion systems, called nodes, which cooperate in order to exchformation without any global control or a centrally maintained global schema. In such an association, called a federatioformation system), the nodes themselves decide the conditions for the exchange and sharing of information. In this thesis, we address three topics in the area of federated information systems: schema integration, schema translation, and interoperability. The thesis is organized as a collection of six self-contained papers. In the first paper, we introduce a logic based framework for conceptual modelling and show how it can be used to clarify and formalize problems in schema integration. In the second paper, we study schema transformations as a means of increasing the similarity between conceptual schemas and thereby facilitating the process of schema comparison. In the third paper, we discuss the notion of schema compatibility, i.e. when a set of schemas can be meaningfully integrated. In the fourth paper, we outline how a semantically rich modelling formalism based on conceptual graph theory can be used to support the identification of correspondences between schemas. In the fifth paper, we describe a method for translating relational schemas into conceptual schemas. In the sixth paper, we discuss interoperability in federated information systems, in particular how agreements between autonomous nodes can be established.