A Proof Procedure for Data Dependencies
Journal of the ACM (JACM)
Foundations of deductive databases and logic programming
Regular path queries with constraints
PODS '97 Proceedings of the sixteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Path constraints on semistructured and structured data
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Interaction between path and type constraints
PODS '99 Proceedings of the eighteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Query rewriting for semistructured data
SIGMOD '99 Proceedings of the 1999 ACM SIGMOD international conference on Management of data
Optimising Web queries using document type definitions
Proceedings of the 2nd international workshop on Web information and data management
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Optimizing Regular Path Expressions Using Graph Schemas
ICDE '98 Proceedings of the Fourteenth International Conference on Data Engineering
Adding Structure to Unstructured Data
ICDT '97 Proceedings of the 6th International Conference on Database Theory
WebOQL: Restructuring Documents, Databases, and Webs
ICDE '98 Proceedings of the Fourteenth International Conference on Data Engineering
DataGuides: Enabling Query Formulation and Optimization in Semistructured Databases
VLDB '97 Proceedings of the 23rd International Conference on Very Large Data Bases
VLDB '99 Proceedings of the 25th International Conference on Very Large Data Bases
Query Optimization for Structured Documents Based on Knowledge on the Document Type Definition
ADL '98 Proceedings of the Advances in Digital Libraries Conference
Query Optimization for Structured Documents Based on Knowledge on the Document Type Definition
ADL '98 Proceedings of the Advances in Digital Libraries Conference
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XQL is one of the query languages proposed for querying XML documents on the world wide web. In this paper, we consider the logical rewriting of XQL query expressions in order to improve the efficiency of query evaluation when XML document type definitions (DTDs) are present. We first define three classes of constraint which can be derived from a given DTD. With a suitable representation of an XML repository R as a relational database D, it turns out that these DTD constraints correspond to tuple- and equality-generating dependencies which must hold on D. Next, we identify a subset of XQL queries on R which is equivalent to a class of conjunctive queries on D. Given a conjunctive query C equivalent to an XQL query Q, we then apply techniques from relational dependency theory to reduce the number of conjuncts in C, yielding query C′. Conjunctive query C′ can then be mapped back to an XQL query Q′ in which redundant filter subexpressions and unnecessary selections have been removed. Whether Q′ can be evaluated more efficiently than Q depends on whether or not appropriate indices exist in R. However, the techniques presented in this paper can provide a query optimizer with a set of equivalent XQL expressions from which to select the best. The representation of queries in relational form and of constraints as dependencies should also permit the application of these results to other XML query languages.