An entity-based approach to query processing in relational databases: Part II: Entity query construction and updating

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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 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.

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      Citation Excerpt :

      Our purpose is to find those factors that facilitate query formulation considerably from the viewpoint of the user. We have developed query languages and techniques for their implementation in terms of which specification related to navigation [14,15] and restructuring [27,28] among data can be removed from the user. Likewise we have shown that in deductive databases complex recursive rule definitions for transitive processing can be replaced by a set of operations intuitive to the user [24,25].

    1

    Timo Niemi received his Ph.D. degree in Computer Science from the University of Tampere in 1985. He has worked as an Assistant Professor in the Department of Computer Science of the same university since 1986. His research interests cover data models, deductive databases, data conversion, database software specification, query languages and logic programming. He has published several articles on these topics in refereed international journals and conferences. He also teaches logic programming at the Department of Computer Science.

    2

    Kalervo Järvelin received his D.Soc.Sci. (Information Retrieval) degree from the University of Tampere in 1986. He has been an Associate Professor in Information Science since 1988 in the Department of Information Studies of the same university. His research interests cover databases and information retrieval. He has published several articles on these topics in refereed international journals and conferences. He also teaches information retrieval at the Department of Information Studies.

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