Approximation in Databases

Partial information in databases can arise when information from several databases is combined. Even if each database is complete for some \world", the combined databases will not be, and answers to queries against such combined databases can only be approximated. In this paper we describe various situations in which a precise answer cannot be obtained for a query asked against multiple databases. Based on an analysis of these situations, we propose a classi cation of constructs that can be used to model approximations. The main goal of the paper is to study several formal models of approximations and their semantics. In particular, we obtain universality properties for these models of approximations. Universality properties suggest syntax for languages with approximations based on the operations which are naturally associated with them. We prove universality properties for most of the approximation constructs. Then we design languages built around datatypes given by the approxim...

• Type: Conference
• Year: 1995
• Where: ICDT
• Authors: Leonid Libkin
• Keywords: Approximation Constructs, Database, Databases, ICDT 1995, Universality Properties