Constructing highly-available distributed metainformation systems
This thesis demonstrates the adequacy of an object-oriented approach to the construction of distributed metainformation systems: systems that facilitate information use by maintaining some information about the information. Computer systems are increasingly being used to store information objects and make them accessible via network. This access, however, still relies on an adequate metainformation system: there must be an effective means of specifying relevant information objects. Moreover, distribution requires the metainformation system to cope well with intermittent availability of network resources. Typical metainformation systems developed to date permit information objects to be specified by expressing knowledge about their syntactic properties, such as keywords. Within this approach, however, query results are potentially too large to be transmitted, stored and treated, at reasonable cost and time. Users are therefore finding it difficult to navigate their way through the masses of information available. In contrast, this thesis is based on the principle that a metainformation system IS more effective if it permits information objects to be specified according to their semantic properties, and that this helps managing, filtering and navigating information. Of particular interest is object orientation because it is the stateof- the-art approach to both the representation of information semantics and the Abstract 11 design of reliable systems. The thesis presents the design and implementation of a programming toolkit for the construction of metainformation systems, where information objects can be any entity that contains information, the notion of views permits organising the information space, transactional access is employed to obtain consistency, and replication is employed to obtain high availability and scalability.