Queries with Incomplete Answers over Semistructured Data

Semistructured data occur in situations where information lacks a homogeneous structure and is incomplete. Yet, up to now the incompleteness of information has not been re ected by special features of query languages. Our goal is to investigate the principles of queries that allow for incomplete answers. We do not present, however, a concrete query language. Queries over classical structured data models contain a number of variables and constraints on these variables. An answer is a binding of the variables by elements of the database such that the constraints are satis ed. In the present paper, we loosen this concept in so far as we allow also answers that are partial, that is, not all variables in the query are bound by such an answer. Partial answers make it necessary to re ne the model of query evaluation. The rst modi cation relates to the satisfaction of constraints: under some circumstances we consider constraints involving unbound variables as satis ed. Second, in order to pre...

• Type: Conference
• Year: 1999
• Where: PODS
• Authors: Yaron Kanza, Werner Nutt, Yehoshua Sagiv
• Keywords: Database, PODS 1999, Query Evaluation, Query Language, Search Phase