On generating all maximal independent sets
Information Processing Letters
Conjunctive query containment revisited
Theoretical Computer Science - Special issue on the 6th International Conference on Database Theory—ICDT '97
Journal of Computer and System Sciences - 30th annual ACM symposium on theory of computing
A comparison of structural CSP decomposition methods
Artificial Intelligence
Query evaluation via tree-decompositions
Journal of the ACM (JACM)
Information Integration Using Logical Views
ICDT '97 Proceedings of the 6th International Conference on Database Theory
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
View matching for outer-join views
VLDB '05 Proceedings of the 31st international conference on Very large data bases
Full disjunctions: polynomial-delay iterators in action
VLDB '06 Proceedings of the 32nd international conference on Very large data bases
From SPARQL to rules (and back)
Proceedings of the 16th international conference on World Wide Web
Algorithms for acyclic database schemes
VLDB '81 Proceedings of the seventh international conference on Very Large Data Bases - Volume 7
Scalable semantic web data management using vertical partitioning
VLDB '07 Proceedings of the 33rd international conference on Very large data bases
SPARQL basic graph pattern optimization using selectivity estimation
Proceedings of the 17th international conference on World Wide Web
Hexastore: sextuple indexing for semantic web data management
Proceedings of the VLDB Endowment
Column-store support for RDF data management: not all swans are white
Proceedings of the VLDB Endowment
An Experimental Comparison of RDF Data Management Approaches in a SPARQL Benchmark Scenario
ISWC '08 Proceedings of the 7th International Conference on The Semantic Web
The Expressive Power of SPARQL
ISWC '08 Proceedings of the 7th International Conference on The Semantic Web
Semantics and complexity of SPARQL
ACM Transactions on Database Systems (TODS)
The RDF-3X engine for scalable management of RDF data
The VLDB Journal — The International Journal on Very Large Data Bases
Foundations of SPARQL query optimization
Proceedings of the 13th International Conference on Database Theory
Proceedings of the twenty-ninth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Structural tractability of enumerating CSP solutions
CP'10 Proceedings of the 16th international conference on Principles and practice of constraint programming
Foundations of Semantic Web databases
Journal of Computer and System Sciences
Querying semantic web data with SPARQL
Proceedings of the thirtieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
What are real SPARQL queries like?
Proceedings of the International Workshop on Semantic Web Information Management
ISWC'11 Proceedings of the 10th international conference on The semantic web - Volume Part I
Containment and minimization of RDF/S query patterns
ISWC'05 Proceedings of the 4th international conference on The Semantic Web
Semantics and complexity of SPARQL
ISWC'06 Proceedings of the 5th international conference on The Semantic Web
Static analysis and optimization of semantic web queries
PODS '12 Proceedings of the 31st symposium on Principles of Database Systems
SPAM: a SPARQL analysis and manipulation tool
Proceedings of the VLDB Endowment
On acyclic conjunctive queries and constant delay enumeration
CSL'07/EACSL'07 Proceedings of the 21st international conference, and Proceedings of the 16th annuall conference on Computer Science Logic
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Static analysis is a fundamental task in query optimization. In this article we study static analysis and optimization techniques for SPARQL, which is the standard language for querying Semantic Web data. Of particular interest for us is the optionality feature in SPARQL. It is crucial in Semantic Web data management, where data sources are inherently incomplete and the user is usually interested in partial answers to queries. This feature is one of the most complicated constructors in SPARQL and also the one that makes this language depart from classical query languages such as relational conjunctive queries. We focus on the class of well-designed SPARQL queries, which has been proposed in the literature as a fragment of the language with good properties regarding query evaluation. We first propose a tree representation for SPARQL queries, called pattern trees, which captures the class of well-designed SPARQL graph patterns. Among other results, we propose several rules that can be used to transform pattern trees into a simple normal form, and study equivalence and containment. We also study the evaluation and enumeration problems for this class of queries.