Error Propagation in Distributed Databases

Abstract

An interesting research area for distributed database systems is inaccessibility. Even if part of the database is inaccessible, a query should be evaluated reasonably. This means, that appropriate rules for propagation and minimization of errors induced by inaccessibility are needed. Furthermore, the result of a query in a distributed database system must be regarded to be potentially vague. In this paper we present a hybrid representation for vague sets, that consists of (1) an enumerating part, which contains the elements we could access during query processing, and (2) a descriptive part, which describes the relevant elements we could not access. Further we introduce propagation rules, which can be used to minimize the vagueness of a query result represented in this hybrid way. Thereby, we propose different levels of accuracy for the descriptive part. As far as we know this is the first approach using a descriptive part to qualify the missing elements of a result. An example for the usefulness of the descriptive part arises, if we have to calculate the intersection of two subqueries. Here, the descriptive part of the first operand can be used to check for each element of the second operand, whether it should be part of the first operand, and vice versa.