NDLI: Incremental computation of nested relational query expressions

Content Provider	ACM Digital Library
Author	Mark, Leo Baekgaard, Lars
Copyright Year	1995
Abstract	Efficient algorithms for incrementally computing nested query expressions do not exist. Nested query expressions are query expressions in which selection/join predicates contain subqueries. In order to respond to this problem, we propose a two-step strategy for incrementaly computing nested query expressions. In step (1), the query expression is transformed into an equivalent unnested flat query expression. In step (2), the flat query expression is incrementally computed. To support step (1), we have developed a very concise algebra-to-algebra transformation algorithm, and we have formally proved its correctness. The flat query expressions resulting from the transformation make intensive use of the relational set-difference operator. To support step (2), we present and analyze an efficient algorithm for incrementally computing set differences based on view pointer caches. When combined with existing incremental algorithms for SPJ queries, our incremental set-difference algorithm can be used to compute the unnested flat query expressions efficiently. It is important to notice that without our incremental set-difference algorithm the existing incremental algorithms for SPJ queries are useless for any query involving the set-difference operator, including queries that are not the result of unnesting nested queries.
Starting Page	111
Ending Page	148
Page Count	38
File Format	PDF
ISSN	03625915
e-ISSN	15574644
DOI	10.1145/210197.210198
Volume Number	20
Issue Number	2
Journal	ACM Transactions on Database Systems (TODS)
Language	English
Publisher	Association for Computing Machinery (ACM)
Publisher Date	1995-06-01
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Incremental computation Nested query expressions Set differences Unnesting View pointer caches
Content Type	Text
Resource Type	Article
Subject	Information Systems

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4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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