TY - GEN
T1 - A study of a positive fragment of path queries: Expressiveness, normal form, and minimization
AU - Wu, Y.
AU - Van Gucht, D.
AU - Gyssens, M.
AU - Paredaens, J.
PY - 2009
Y1 - 2009
N2 - We study the expressiveness of a positive fragment of path queries, denoted Path, on node-labeled trees documents. The expressiveness of Path is studied from two angles. First, we establish that Path is equivalent in expressive power to a particular sub-fragment as well as to the class of tree queries, a sub-class of the first-order conjunctive queries defined over label, parent-child, and child-parent predicates. The translation algorithm from tree queries to Path yields a normal form for Path queries. Using this normal form, we can decompose a Path query into sub-queries that can be expressed in a very small sub-fragment of Path for which efficient evaluation strategies are available. Second, we characterize the expressiveness of Path in terms of its ability to resolve nodes in a document. This result is used to show that each tree query can be translated to a unique, equivalent, and minimal tree query. The combination of these results yields an effective strategy to evaluate a large class of path queries on documents.
AB - We study the expressiveness of a positive fragment of path queries, denoted Path, on node-labeled trees documents. The expressiveness of Path is studied from two angles. First, we establish that Path is equivalent in expressive power to a particular sub-fragment as well as to the class of tree queries, a sub-class of the first-order conjunctive queries defined over label, parent-child, and child-parent predicates. The translation algorithm from tree queries to Path yields a normal form for Path queries. Using this normal form, we can decompose a Path query into sub-queries that can be expressed in a very small sub-fragment of Path for which efficient evaluation strategies are available. Second, we characterize the expressiveness of Path in terms of its ability to resolve nodes in a document. This result is used to show that each tree query can be translated to a unique, equivalent, and minimal tree query. The combination of these results yields an effective strategy to evaluate a large class of path queries on documents.
U2 - 10.1007/978-3-642-02843-4_14
DO - 10.1007/978-3-642-02843-4_14
M3 - Conference contribution
SN - 978-3-642-02842-7
T3 - Lecture Notes in Computer Science
SP - 133
EP - 145
BT - Dataspace: The Final Frontier (26th British National Conference on Databases, BNCOD 26, Birmingham, UK, July 7-9, 2009. Proceedings)
A2 - Sexton, A.P.
PB - Springer
CY - Berlin
ER -