Boundedness is undecidable for datalog programs with a single recursive rule
Information Processing Letters
Equivalence of datalog queries is undecidable
Journal of Logic Programming
Equivalences Among Relational Expressions with the Union and Difference Operators
Journal of the ACM (JACM)
Conjunctive-query containment and constraint satisfaction
Journal of Computer and System Sciences - Special issue on the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on principles of database systems
Efficient algorithms for minimizing tree pattern queries
Proceedings of the 2002 ACM SIGMOD international conference on Management of data
Conjunctive Query Containment Revisited
ICDT '97 Proceedings of the 6th International Conference on Database Theory
Containment for XPath Fragments under DTD Constraints
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Structural Properties of XPath Fragments
ICDT '03 Proceedings of the 9th International Conference on Database Theory
XPath Containment in the Presence of Disjunction, DTDs, and Variables
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Tree pattern query minimization
The VLDB Journal — The International Journal on Very Large Data Bases
Optimal implementation of conjunctive queries in relational data bases
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
Containment and equivalence for a fragment of XPath
Journal of the ACM (JACM)
ACM SIGMOD Record
Algorithms for acyclic database schemes
VLDB '81 Proceedings of the seventh international conference on Very Large Data Bases - Volume 7
Efficient algorithms for processing XPath queries
VLDB '02 Proceedings of the 28th international conference on Very Large Data Bases
Taming XPath queries by minimizing wildcard steps
VLDB '04 Proceedings of the Thirtieth international conference on Very large data bases - Volume 30
Revisiting redundancy and minimization in an XPath fragment
EDBT '08 Proceedings of the 11th international conference on Extending database technology: Advances in database technology
On the expressiveness of generalization rules for XPath query relaxation
Proceedings of the Fourteenth International Database Engineering & Applications Symposium
Union rewritings for XPath fragments
Proceedings of the 15th Symposium on International Database Engineering & Applications
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XPath expressions define navigational queries on XML data and are issued on XML documents to select sets of element nodes. Due to the wide use of XPath, which is embedded into several languages for querying and manipulating XML data, the problem of efficiently answering XPath queries has received increasing attention from the research community. As the efficiency of computing the answer of an XPath query depends on its size, replacing XPath expressions with equivalent ones having the smallest size is a crucial issue in this direction. This article investigates the minimization problem for a wide fragment of XPath (namely X P[✶]), where the use of the most common operators (child, descendant, wildcard and branching) is allowed with some syntactic restrictions. The examined fragment consists of expressions which have not been specifically studied in the relational setting before: neither are they mere conjunctive queries (as the combination of “//” and “*” enables an implicit form of disjunction to be expressed) nor do they coincide with disjunctive ones (as the latter are more expressive). Three main contributions are provided. The “global minimality” property is shown to hold: the minimization of a given XPath expression can be accomplished by removing pieces of the expression, without having to re-formulate it (as for “general” disjunctive queries). Then, the complexity of the minimization problem is characterized, showing that it is the same as the containment problem. Finally, specific forms of XPath expressions are identified, which can be minimized in polynomial time.