On conjunctive queries containing inequalities
Journal of the ACM (JACM)
Optimization of real conjunctive queries
PODS '93 Proceedings of the twelfth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Containment of conjunctive queries: beyond relations as sets
ACM Transactions on Database Systems (TODS)
On path equivalence of nondeterministic finite automata
Information Processing Letters
Containment for XPath Fragments under DTD Constraints
ICDT '03 Proceedings of the 9th International Conference on Database Theory
Containment and equivalence for a fragment of XPath
Journal of the ACM (JACM)
Equivalences among aggregate queries with negation
ACM Transactions on Computational Logic (TOCL)
Deciding equivalences among conjunctive aggregate queries
Journal of the ACM (JACM)
The complexity of query containment in expressive fragments of XPath 2.0
Proceedings of the twenty-sixth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Equivalence of queries that are sensitive to multiplicities
The VLDB Journal — The International Journal on Very Large Data Bases
Bag equivalence of XPath queries
Proceedings of the 13th International Conference on Database Theory
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When a query is evaluated under bag semantics, each answer is returned as many times as it has derivations. Bag semantics has long been recognized as important, especially when aggregation functions will be applied to query results. This article is the first to focus on bag semantics for tree pattern queries. In particular, the problem of bag equivalence of a large class of tree pattern queries (which can be used to model XPath) is explored. The queries can contain unions, branching, label wildcards, the vertical child and descendant axes, the horizontal following and following-sibling axes, as well as positional (i.e., first and last) axes. Equivalence characterizations are provided, and their complexity is analyzed. As the descendant axis involves a recursive relationship, this article is also the first to address bag equivalence over recursive queries, in any setting.