Containment of conjunctive queries: beyond relations as sets
ACM Transactions on Database Systems (TODS)
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 tree patterns
ACM Transactions on Database Systems (TODS)
Union rewritings for XPath fragments
Proceedings of the 15th Symposium on International Database Engineering & Applications
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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 paper is the first to focus on bag semantics for XPath queries. In particular, the problem of bag-equivalence of a large class of XPath queries (modeled as tree patterns) is explored. The queries can contain unions, branching, label wildcards, the vertical child and descendant axes, the horizontal following, following-sibling and immediately-following sibling axes, as well as positional (i.e., first and last) axes. Equivalence characterizations are provided, and their complexity is analyzed. As the descendent axis involves a recursive relationship, this paper is also the first to address bag equivalence over recursive queries, in any setting.