TY - GEN
T1 - Finding a minimal tree pattern under neighborhood constraints
AU - Kimelfeld, Benny
AU - Sagiv, Yehoshua
PY - 2011
Y1 - 2011
N2 - Tools that automatically generate queries are useful when schemas are hard to understand due to size or complexity. Usually, these tools find minimal tree patterns that contain a given set (or bag) of labels. The labels could be, for example, XML tags or relation names. The only restriction is that, in a tree pattern, adjacent labels must be among some specified pairs. A more expressive framework is developed here, where a schema is a mapping of each label to a collection of bags of labels. A tree pattern conforms to the schema if for all nodes v, the bag comprising the labels of the neighbors is contained in one of the bags to which the label of v is mapped. The problem at hand is to find a minimal tree pattern that conforms to the schema and contains a given bag of labels. This problem is NP-hard even when using the simplest conceivable language for describing schemas. In practice, however, the set of labels is small, so efficiency is realized by means of an algorithm that is fixedparameter tractable (FPT). Two languages for specifying schemas are discussed. In the first, one expresses pairwisemutual exclusions between labels. Though W[1]-hardness (hence, unlikeliness of an FPT algorithm) is shown, an FPT algorithm is described for the case where the mutual exclusions form a circular-arc graph (e.g., disjoint cliques). The second language is that of regular expressions, and for that another FPT algorithm is described.
AB - Tools that automatically generate queries are useful when schemas are hard to understand due to size or complexity. Usually, these tools find minimal tree patterns that contain a given set (or bag) of labels. The labels could be, for example, XML tags or relation names. The only restriction is that, in a tree pattern, adjacent labels must be among some specified pairs. A more expressive framework is developed here, where a schema is a mapping of each label to a collection of bags of labels. A tree pattern conforms to the schema if for all nodes v, the bag comprising the labels of the neighbors is contained in one of the bags to which the label of v is mapped. The problem at hand is to find a minimal tree pattern that conforms to the schema and contains a given bag of labels. This problem is NP-hard even when using the simplest conceivable language for describing schemas. In practice, however, the set of labels is small, so efficiency is realized by means of an algorithm that is fixedparameter tractable (FPT). Two languages for specifying schemas are discussed. In the first, one expresses pairwisemutual exclusions between labels. Though W[1]-hardness (hence, unlikeliness of an FPT algorithm) is shown, an FPT algorithm is described for the case where the mutual exclusions form a circular-arc graph (e.g., disjoint cliques). The second language is that of regular expressions, and for that another FPT algorithm is described.
KW - Graph search
KW - Minimal tree pattern
KW - Query extraction
UR - http://www.scopus.com/inward/record.url?scp=79960160123&partnerID=8YFLogxK
U2 - https://doi.org/10.1145/1989284.1989318
DO - https://doi.org/10.1145/1989284.1989318
M3 - منشور من مؤتمر
SN - 9781450306607
T3 - Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems
SP - 235
EP - 246
BT - PODS'11 - Proceedings of the 30th Symposium on Principles of Database Systems
T2 - 30th Symposium on Principles of Database Systems, PODS'11
Y2 - 13 May 2011 through 15 May 2011
ER -