Incremental computation of nested relational query expressions

Journal Article · Thu Jun 01 04:00:00 EDT 1995 · ACM Transactions on Database Systems

DOI:https://doi.org/10.1145/210197.210198· OSTI ID:273027

Baekgaard, L ^[1]; Mark, L ^[2]

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1. Aalborg Univ. (Denmark)
2. Georgia Institute of Technology, Atlanta, GA (United States)

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 incrementally 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. 45 refs., 4 figs., 5 tabs.

• OSTI ID: 273027
• Journal Information: ACM Transactions on Database Systems, Journal Name: ACM Transactions on Database Systems Journal Issue: 2 Vol. 20; ISSN 0362-5915; ISSN ATDSD3
• Country of Publication: United States
• Language: English

Related Subjects

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ALGORITHMS
DATA BASE MANAGEMENT
DATA PROCESSING
INFORMATION RETRIEVAL
MATHEMATICAL LOGIC
PERFORMANCE
PROGRAMMING LANGUAGES