An Entity-Based Approach to Query Processing in Relational Databases. Part II: Entity Query Construction and Updating

Kalervo Järvelin# and Timo Niemi+

#Department of Information Studies
+Department of Computer Science University of Tampere
P.O.Box 607
FIN-33101 TAMPERE, Finland

Data & Knowledge Engineering 10, 1993: 151-186

Abstract

A declarative entity-based query language called the E-TRC for relational databases is presented and the construction and evaluation process of RA queries for its expressions is developed. This extends the value-oriented entity representation and the entity-based window generator for entity type projections of Part I. It is also shown how entity-level update transactions can be interpreted in a logical and consistent way and targeted to suitable relations while maintaining database integrity.

The query construction and evaluation process derives the entity type and instance for query results automatically. The construction process solves query interpretation problems and improves query efficiency e.g. by rejecting semantically incorrect interpretations. The semantics of query results are thus also clear and accurate. This facilitates the formulation of a complex queries which become simpler and more comprehensible than corresponding RA expressions. The declarativeness of the E-TRC increases its user-friendliness. The expressive power of E-TRC is of the level of Quel. Disjunctions are allowed in the predicates of E-TRC. This increases its expressive power and extends optimization beyond conjunctive queries. Because the query construction process constructs RA expressions, they can be optimized and evaluated by existing well-tested RDBMSs. The query construction process defines the semantics of the E-TRC language formally in terms of equivalent RA expressions.

The entity types provide the users with a high-level and natural view of the database. The users express all query and update transactions in terms of the entity types. This simplifies the expression of complex transactions considerably w.r.t. conventional systems. The interface exploits this knowledge in an effective way.

Keywords: universal relation databases, complex entity types, high-level query languages, query construction and optimization, ambiguity resolution, updating.

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