Entity join optimization in multidatabase systems.

Content Provider	CiteSeerX
Author	Tsai, Pauray S. M. Chen, Arbee L. P.
Abstract	Heterogeneities exist in a multidatabase environment. For example, a real world entity may be di erently represented in relations of di erent databases. In particular, keys of these relations may be incompatible. In this paper, we develop an entity join operator named EJ operator, which can be used to join two relations on their compatible/incompatible keys. By this join, if an entity is represented in both relations, all its properties given in relations can be obtained. Besides, a neighborhood join operator named NJ operator is introduced, which joins relations allowing some degree of value uncertainty onthe join attributes. The EJ operator, NJ operator and the previously proposed extended relational operators can be combined to support a more powerful set of operations for a multidatabase system. We consider processing entity join queries in a wide area multidatabase environment where the query processing cost is dominated by the cost of data transmission. Since the EJ operator "integrates " tuples from relations, whose attribute values may have con icts, a natural way to process the operator is to transmit both relations to a site, resolve the con icts and process the join, which isvery costly. An approach which transforms a global query into local subqueries to preprocess queries with EJs in multiple sites is thus proposed with an attempt to lower the cost of data transmission. 1
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Subject Keyword	Multiple Site Local Subqueries Natural Way Value Uncertainty Entity Join Operator Query Processing Cost Global Query Neighborhood Join Operator Join Attribute Multidatabase System Ej Operator Quot Ej Operator Powerful Set Nj Operator Wide Area Multidatabase Environment Data Transmission Con Icts Di Erent Database Multidatabase Environment Attribute Value Compatible Incompatible Key Entity Join Query Relational Operator Entity Join Optimization Real World Entity
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