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 (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 D¯ with respect to D .
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
