Date of Award

Spring 1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Computing Sciences - (Ph.D.)

Department

Computer and Information Science

First Advisor

Yehoshua Perl

Second Advisor

James Geller

Third Advisor

James A. McHugh

Fourth Advisor

Bonnie Kathleen MacKellar

Fifth Advisor

Jason T. L. Wang

Sixth Advisor

Aaron Watters

Abstract

A path-method is a mechanism in object-oriented databases (OODBs) to retrieve or to update information relevant to one class that is not stored with that class but with some other class. A path-method is a method which traverses from one class through a chain of connections between classes to access information at another class. However, it is a difficult task for a user to write path-methods, because it might require comprehensive knowledge of many classes of the conceptual schema, while a typical user has often incomplete or even inconsistent knowledge of the schema.

This dissertation proposes an approach to the generation of path-methods in an OODB to solve this problem. We have developed the Path-Method Generator (P MG) system, which generates path-methods according to a naive user's requests. PMG is based on access weights which reflect the relative frequency of the connections and precomputed access relevance between every pair of classes of the OODB computed from access weights of the connections. We present specific rules for access weight assignment, efficient algorithms to compute access relevance in a single OODB, and a variety of traversal algorithms based on access weights and precomputed access relevance. Experiments with a university environment OODB and a sample of path-methods identify some of these algorithms as very successful in generating most of the desired path-methods. Thus, the PMG system is an efficient tool for aiding the user with the difficult task of querying and updating a large OODB.

The path-method generation in an interoperable multi object-oriented database (IM-OODB) is even more difficult than for a single OODB, since a user has to be familiar with several OODBs. We use a hierarchical approach for deriving efficient online algorithms for the computation of access relevance in an IM-OODB, based on precomputed access relevance for each autonomous OODB. In an IM-OODB the access relevance is used as guide in generating path-methods between the classes of different OODBs.

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