Solving implication problems in database applications

Sun, Xian-He; Kamel, Nabil; Ni, Lionel M.

doi:10.1145/66926.66943

Cited by 12 publications

(5 citation statements)

References 8 publications

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“…Since the problem of query derivability in general is NP-hard [31], the focus of this article is not to investigate all possibilities of the derivability of relational queries. Instead, we restrict the scope of interest to the typical class of data warehouse queries: star (or snowflake) queries with aggregations and restrictions on measures possibly computed like Turnover in section 2.…”

Section: Aggregate Viewsmentioning

confidence: 99%

Query optimization by using derivability in a data warehouse environment

Albrecht

Hümmer

Lehner

et al. 2000

Proceedings of the 3rd ACM International Workshop on Data Warehousing and OLAP

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Materialized summary tables and cached query results are frequently used for the optimization of aggregate queries in a data warehouse. Query rewriting techniques are incorporated into database systems to use those materialized views and thus avoid the access of the possibly huge raw data. A rewriting is only possible if the query is derivable from these views. Several approaches can be found in the literature to check the derivability and find query rewritings. The specific application scenario of a data warehouse with its multidimensional perspective allows the consideration of much more semantic information, e.g. structural dependencies within the dimension hierarchies and different characteristics of measures. The motivation of this article is to use this information to present conditions for derivability in a large number of relevant cases which go beyond previous approaches. MOTIVATIONWe will motivate our case with an illustrative example. Consider the conceptual schema of the data warehouse of some retail store chain as depicted in figure 1. By adopting a multidimensional terminology, there are three dimensions, Product, Location and Time with several category attributes. The arrows define functional dependencies in database terms. Each path from a terminal attribute, e.g. Article, to the Top category in the respective dimension defines a classification hierarchy (figure 1). Parallel paths result in parallel hierar-

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Section: Aggregate Viewsmentioning

confidence: 99%

Query optimization by using derivability in a data warehouse environment

Albrecht

Hümmer

Lehner

et al. 2000

Proceedings of the 3rd ACM International Workshop on Data Warehousing and OLAP

View full text Add to dashboard Cite

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“…Rosenkrantz and Hunt [13] give a digraph representation of a special class of predicates and give polynomial time algorithms for the satisfiability, equivalence and reduction problems when the ~ sign is not permitted. Thus, this work is also related to work done on fragments of relations.…”

Section: Related Workmentioning

confidence: 99%

“…The query model: The basis for our query model is the conjunctive unequalsfree mixed predicate [13]. A list of the general notation used throughout the paper can be found in the appendix.…”

Section: Query Model Usage Pattern Model Disk Model and General Nomentioning

confidence: 99%

Page-query compaction of secondary memory auxiliary databases

Kamel

1994

Distrib Parallel Databases

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Prestoring redundant data in secondary memory auxiliary databases is an idea that can often yield improved retrieval performance through better clustering of related data. The clusters can be based on either whole query results or, as this paper indicates, on more specialized units called page-queries. The deliberate redundancy introduced by the designer is typically accompanied by much unnecessary redundancy among the elements of the auxiliary database. This paper presents algorithms for efficiently removing unwanted redundancy in auxiliary databases organized into page-query units. The algorithms presented here extend prior work done for secondary memory compaction in two respects: First, since it is generally not possible to remove all unwanted redundancies, the paper shows how can the compaction be done to remove the most undesirable redundancy from a system performance point-of-view. For example, among the factors considered in determining the worst redundancies are the update behavior and the effects of a particular compaction scheme on memory utilization. Second, unlike traditional approaches for database compaction which aim merely at reducing the storage space, this paper considers the paging characteristics in deciding on an optimal compaction scheme. This is done through the use of page-queries. Simulation results are presented and indicate that page-query compaction results in less storage requirements and more time savings than could be obtained by standard non-page-query compaction.

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“…Multiple query optimization has received extensively research attention in traditional centralized database systems and many techniques have been proposed in this context [11,21,19,12,14,9,15,18]. Multiple query optimization exploits the fact that a sequence of complex queries can share common subexpressions which can be recognized and reused to reduce the cost of query evaluation.…”

Section: Introductionmentioning

confidence: 99%