Utilizing integrity constraint knowledge in heterogeneous databases: A methodology for schema integration and semantic query processing.

Abstract

Information sharing among databases requires the development of techniques for accessing data from multiple heterogeneous databases. One approach to providing interoperability among these databases, is to define one or more schemas representing a coherent view of the underlying databases. A review of existing research on schema integration, the process of generating integrated schemas, points to the need for development of techniques for identifying objects in multiple databases that may be related. The development of efficient mechanisms for accessing heterogeneous databases is another issue that has received very little attention in the literature. This dissertation describes a seven step methodology for utilizing integrity constraint knowledge from multiple heterogeneous databases. The methodology extends traditional approaches to schema integration by proposing additional steps that describe how integrity constraints can be used, in a heterogeneous database environment, to improve the interschema relationship identification process and generate additional semantics, in the form of integrity constraints, at the integrated schema level. The dissertation introduces the concept of constraint-based relationships among objects in heterogeneous databases and describes how these relationships can be used to integrate integrity constraints specified on heterogeneous databases. The dissertation also elaborates on how these integrated integrity constraints can be used to facilitate semantic query processing in a heterogeneous database environment. The description of a system that implements the various phases of the methodology is also presented. A unique feature of the system is that it uses blackboard architectures to facilitate the human-computer interaction needed during schema integration. A simulation study that shows the potential benefits of performing semantic query processing, in a heterogeneous database environment, using the integrated integrity constraints generated by our methodology is also presented.