Constrained query tree is introduced as the multidatabase query representation, it is shown that some knowledge about query predicates and attribute derivation functions can be used to simplify queries. Such knowledge is modeled as an outerjoin graph attached to every outerjoin operation in the query tree. Based on this, the traditional algebraic transformation framework is extended to include two-way outerjoins and GAD operations. The framework demonstrates that properties of selection/join predicates and attribute derivative functions can be used to provide interesting transformation alternative. This framework also serves as a formal ground for developing optimization strategies for multidatabase queries.
|Number of pages||35|
|Journal||Distributed and Parallel Databases|
|Publication status||Published - Jul 1995|
ASJC Scopus subject areas
- Computational Theory and Mathematics
- Information Systems
- Theoretical Computer Science