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Answering queries using views with arithmetic comparisons

by Foto Afrati, Chen Li, Prasenjit Mitra - Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS , 2002
"... We consider the problem of answering queries using views, where queries and views are conjunctive queries with arithmetic comparisons (CQACs) over dense orders. Previous work only considered limited variants of this problem, without giving a complete solution. We have developed an ecient algorithm t ..."
Abstract - Cited by 29 (14 self) - Add to MetaCart
We consider the problem of answering queries using views, where queries and views are conjunctive queries with arithmetic comparisons (CQACs) over dense orders. Previous work only considered limited variants of this problem, without giving a complete solution. We have developed an ecient algorithm to obtain maximally contained rewritings (MCRs) for queries having left (or right) semi-interval-comparison predicates. For semi-interval queries we show that at least recursive datalog is necessary to nd a maximally-contained solution, and identify cases where datalog is sucient. Finally, we show that obtaining equivalent rewritings for CQAC's is decidable
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Semantic Optimization of Preference Queries

by Jan Chomicki , 2004
"... Preference queries are relational algebra or SQL queries that contain occurrences of the winnow operator (find the most preferred tuples in a given relation). We present here a number of semantic optimization techniques applicable to preference queries. The techniques make it possible to remove red ..."
Abstract - Cited by 26 (2 self) - Add to MetaCart
Preference queries are relational algebra or SQL queries that contain occurrences of the winnow operator (find the most preferred tuples in a given relation). We present here a number of semantic optimization techniques applicable to preference queries. The techniques make it possible to remove redundant occurrences of the winnow operator and to apply a more efficient algorithm for the computation of winnow. We also study the propagation of integrity constraints in the result of the winnow. We have identified necessary and sufficient conditions for the applicability of our techniques, and formulated those conditions as constraint satisfiability problems.

Efficient XML-to-SQL Query Translation: Where to Add the Intelligence?

by Rajasekar Krishnamurthy, Raghav Kaushik, Jeffrey F Naughton - In VLDB , 2004
"... We consider the efficiency of queries generated by XML to SQL translation. We first show that published XML-to-SQL query translation algorithms are suboptimal in that they often translate simple path expressions into complex SQL queries even when much simpler equivalent SQL queries exist. There are ..."
Abstract - Cited by 23 (1 self) - Add to MetaCart
We consider the efficiency of queries generated by XML to SQL translation. We first show that published XML-to-SQL query translation algorithms are suboptimal in that they often translate simple path expressions into complex SQL queries even when much simpler equivalent SQL queries exist. There are two logical ways to deal with this problem. One could generate suboptimal SQL queries using a fairly naive translation algorithm, and then attempt to optimize the resulting SQL; or one could use a more intelligent translation algorithm with the hopes of generating efficient SQL directly. We show that optimizing the SQL after it is generated is problematic, becoming intractable even in simple scenarios; by contrast, designing a translation algorithm that exploits information readily available at translation time is a promising alternative. To support this claim, we present a translation algorithm that exploits translation time information to generate efficient SQL for path expression queries over tree schemas.
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Semantic Optimization Techniques for Preference Queries

by Jan Chomicki , 2006
"... Preference queries are relational algebra or SQL queries that contain occurrences of the winnow operator (find the most preferred tuples in a given relation). Such queries are parameterized by specific preference relations. Semantic optimization techniques make use of integrity constraints holding i ..."
Abstract - Cited by 15 (4 self) - Add to MetaCart
Preference queries are relational algebra or SQL queries that contain occurrences of the winnow operator (find the most preferred tuples in a given relation). Such queries are parameterized by specific preference relations. Semantic optimization techniques make use of integrity constraints holding in the database. In the context of semantic optimization of preference queries, we identify two fundamental properties: containment of preference relations relative to integrity constraints and satisfaction of order axioms relative to integrity constraints. We show numerous applications of those notions to preference query evaluation and optimization. As integrity constraints, we consider constraint-generating dependencies, a class generalizing functional dependencies. We demonstrate that the problems of containment and satisfaction of order axioms can be captured as specific instances of constraintgenerating dependency entailment. This makes it possible to formulate necessary and sufficient conditions for the applicability of our techniques as constraint validity problems. We characterize the computational complexity of such problems.

Optimizing Queries in Extended Relational Databases

by Michael Maher, Junhu Wang - In International Conference on Database and Expert Systems Applications (DEXA
"... . We investigate the optimization of extended relational queries used in systems holding, for example, spatial, multimedia or constraint data. For such queries we must account for the built-in relations specic to the kind of data, and application dependent relationships between different relatio ..."
Abstract - Cited by 10 (4 self) - Add to MetaCart
. We investigate the optimization of extended relational queries used in systems holding, for example, spatial, multimedia or constraint data. For such queries we must account for the built-in relations specic to the kind of data, and application dependent relationships between different relations. We show that the constraint database perspective and the use of constrained tuple-generating dependencies provides a general framework in which to address semantic query optimization for these queries. We establish some sucient conditions for query transformations involving the introduction or deletion of relations, extending work in the literature for conventional databases. We introduce semantic query partition (SQP) as a useful technique for optimizing queries with expensive operations, and investigate the problem of generating subqueries, which is central to the use of SQP. In general, our results suggest the use of union queries, but we establish general cases where unions...

On the finite controllability of conjunctive query answering in . . .

by Riccardo Rosati , 2010
"... ..."
Abstract - Cited by 9 (0 self) - Add to MetaCart
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Reasoning with Disjunctive Constrained Tuple-Generating Dependencies

by Junhu Wang, Rodney Topor, Michael Maher - In DEXA , 2001
"... . In extended relational databases, queries and integrity constraints often contain interpreted variables and built-in relations. We extend previous work on semantic query containment for extended relational databases to handle disjunctive constrained tuple-generating dependencies (DCTGDs) which inc ..."
Abstract - Cited by 5 (0 self) - Add to MetaCart
. In extended relational databases, queries and integrity constraints often contain interpreted variables and built-in relations. We extend previous work on semantic query containment for extended relational databases to handle disjunctive constrained tuple-generating dependencies (DCTGDs) which include almost all well-known classes of integrity constraints. After de ning this extended class of integrity constraints, we present a method for expanding a query Q, using DCTGDs, to a semantically equivalent set of queries. Our theorems on this method unify and generalize several previous results on semantic query containment. We apply the method to the DCTGD implication problem and prove that, when restricted to regular CTGDs, our method is strictly more powerful than previously published chase algorithms. 1
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Optimizing fixed-schema XML to SQL query translation

by Rajasekar Krishnamurthy, Raghav Kaushik, Jeffrey F. Naughton - IN VLDB , 2002
"... Recently, there has been a lot of work on evaluating XML queries over data stored in rela-tional database systems. The vast majority of this work has focused on the cases where either the relational schema is not fixed (so the problem is to find a good relational schema for a given XML workload) or ..."
Abstract - Cited by 3 (1 self) - Add to MetaCart
Recently, there has been a lot of work on evaluating XML queries over data stored in rela-tional database systems. The vast majority of this work has focused on the cases where either the relational schema is not fixed (so the problem is to find a good relational schema for a given XML workload) or the XML schema is not fixed (so the problem is to develop generic strategies for exporting XML views of relational data). While these cases are interesting, in practice a third scenario, in which both the source relational and target XML schemas are fixed, seems highly relevant. We show that even in this highly constrained environment, there is a lot of freedom in the SQL that can be generated to evaluate a given XML query. Furthermore, we show through experiments with a commercial RDBMS that by exploiting the underlying relational constraints and the properties of a given XML to relational schema mapping, it is possible to generate SQL queries that perform an order of magnitude better than those generated by more naive translations. Motivated by these performance-enhancing opportunities, we present a constraint-aware XML to SQL query translation algorithm for path expression queries.
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Unraveling the Duplicate-Elimination Problem in XML-to-SQL Query Translation

by Rajasekar Krishnamurthy, Raghav Kaushik, Jeffrey F Naughton - In Proceedings of the Seventh International Workshop on the Web and Databases (WebDB , 2004
"... We consider the scenario where existing relational data is exported as XML. In this context, we look at the problem of translating XML queries into SQL. XML query languages have two di#erent notions of duplicates: node-identity based and value-based. Path expression queries have an implicit node-ide ..."
Abstract - Cited by 2 (1 self) - Add to MetaCart
We consider the scenario where existing relational data is exported as XML. In this context, we look at the problem of translating XML queries into SQL. XML query languages have two di#erent notions of duplicates: node-identity based and value-based. Path expression queries have an implicit node-identity based duplicate elimination built into them. On the other hand, SQL only supports value-based duplicate elimination. In this paper, using a simple path expression query we illustrate the problems that arise when we attempt to simulate the node-identity based duplicate elimination using value-based duplicate elimination in the SQL queries. We show how a general solution for this problem covering the class of views considered in published literature requires a fairly complex mechanism.
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Open Issues in Semantic Query Optimization in Related DBMS”, IV. Working paper series

by Bryan Genet, Annika Hinze
"... After two decades of research into Semantic Query Optimization (SQO) there is clear agreement as to the efficacy of SQO. However, although there are some experimental implementations there are still no commercial implementations. We first present a thorough analysis of research into SQO. We identify ..."
Abstract - Cited by 2 (0 self) - Add to MetaCart
After two decades of research into Semantic Query Optimization (SQO) there is clear agreement as to the efficacy of SQO. However, although there are some experimental implementations there are still no commercial implementations. We first present a thorough analysis of research into SQO. We identify three problems which inhibit the effective use of SQO in Relational Database Management Sys-tems (RDBMS). We then propose solutions to these problems and describe first steps towards the implementation of an effective semantic query optimizer for re-