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 are equivalent to the existence of a tree projection of D with respect to D. These properties amount to the ability to efficiently compute the join of all the relations in a state for D from an extension of this state over 15. The equivalence is proved for unrestricted (i.e., both finite and infinite) 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 5 with respect to D.
Original language | English |
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Pages | 160-172 |
Number of pages | 13 |
DOIs | |
State | Published - 1986 |
Event | 5th ACM SIGACT-SIGMOD Symposium on Principles of Database Systems, PODS 1986 - Cambridge, United States Duration: 24 Mar 1986 → 26 Mar 1986 |
Conference
Conference | 5th ACM SIGACT-SIGMOD Symposium on Principles of Database Systems, PODS 1986 |
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Country/Territory | United States |
City | Cambridge |
Period | 24/03/86 → 26/03/86 |
Bibliographical note
Publisher Copyright:© 1986.