TY - GEN
T1 - Flexible queries over semistructured data
AU - Kanza, Y.
AU - Sagiv, Y.
PY - 2001/5/1
Y1 - 2001/5/1
N2 - Flexible queries facilitate, in a novel way, easy and concise querying of databases that have varying structures. Two different semantics, flexible and semiflexible, are introduced and investigated. The complexity of evaluating queries under the two semantics is analyzed. Query evaluation is polynomial in the size of the query, the database and the result in the following two cases. First, a semiflexible DAG query and a tree database. Second, a flexible tree query and a database that is any graph. Query containment and equivalence are also investigated. For the flexible semantics, query equivalence is always polynomial. For the semiflexible semantics, query equivalence is polynomial for DAG queries and exponential when the queries have cycles. Under the semiflexible and flexible semantics, two databases could be equivalent even when they are not isomorphic. Database equivalence is formally defined and characterized. The complexity of deciding equivalences among databases is analyzed. The implications of database equivalence on query evaluation are explained.
AB - Flexible queries facilitate, in a novel way, easy and concise querying of databases that have varying structures. Two different semantics, flexible and semiflexible, are introduced and investigated. The complexity of evaluating queries under the two semantics is analyzed. Query evaluation is polynomial in the size of the query, the database and the result in the following two cases. First, a semiflexible DAG query and a tree database. Second, a flexible tree query and a database that is any graph. Query containment and equivalence are also investigated. For the flexible semantics, query equivalence is always polynomial. For the semiflexible semantics, query equivalence is polynomial for DAG queries and exponential when the queries have cycles. Under the semiflexible and flexible semantics, two databases could be equivalent even when they are not isomorphic. Database equivalence is formally defined and characterized. The complexity of deciding equivalences among databases is analyzed. The implications of database equivalence on query evaluation are explained.
UR - https://www.scopus.com/pages/publications/0034826250
U2 - 10.1145/375551.375558
DO - 10.1145/375551.375558
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AN - SCOPUS:0034826250
T3 - Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems
SP - 40
EP - 51
BT - Proceedings of the 20th ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems, PODS 2001
PB - Association for Computing Machinery (ACM)
T2 - 20th ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems, PODS 2001
Y2 - 21 May 2001 through 23 May 2001
ER -