Abstract
Suppose a database schema D is extended to D¯ by adding new relation schemas, and states for D are extended to states for D¯ by applying joins and projections to existing relations. It is shown that certain desirable properties that D¯ has with respect to D. These properties amount to the ability to compute efficiently the join of all relations in a state for D from an extension of this state over D¯. The equivalence is proved for unrestricted 1993 databases. If D¯ is obtained from D by adding a set of new relation schemas that form a tree schema, then the equivalence also holds for finite databases. In this case there is also a polynomial time algorithm for testing the existence of a tree projection of D¯ with respect to D.
Original language | English |
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Pages (from-to) | 487-511 |
Number of pages | 25 |
Journal | ACM Transactions on Database Systems |
Volume | 18 |
Issue number | 3 |
DOIs | |
State | Published - 9 Jan 1993 |
Keywords
- Acyclicity
- chase
- database schema
- hypergraph
- inclusion dependency
- join
- monotone join expression
- projection
- qual graph
- relational database
- semijoin
- semijoin reduction
- tableau
- tree projection
- tree schema