A Chase-based Approach to Consistent Answers of Analytic Queries in Star Schemas

TL;DR

This paper introduces polynomial-time algorithms for computing consistent answers to analytic queries, including aggregates, in star schema data warehouses with possible data inconsistencies and missing values.

Contribution

It extends previous work on consistent query answering to include aggregate and analytic queries in star schemas, with algorithms for cases satisfying independence conditions.

Findings

Algorithms run in O(W.log(W)) time, where W is data warehouse size.

Provides exact consistent answers for analytic queries with certain selection conditions.

Addresses handling of having and group-by clauses in the context of data inconsistencies.

Abstract

We present an approach to computing consistent answers to queries possibly involving an aggregation operator in databases operating under a star schema and possibly containing missing values and inconsistent data. Our approach is based on earlier work concerning consistent query answering for standard queries (with no aggregate operator) in multi-table databases. In that work, we presented polynomial algorithms for computing either the exact consistent answer to a query or bounds of the exact answer, depending on whether the query involves a selection condition or not. In the present work, we consider databases operating under a star schema. Calling data warehouses such databases, we extend our previous work to queries involving aggregate operators, called analytic queries. In this context, we propose specific algorithms for computing exact consistent answers to queries, whether analytic or not, provided that the selection condition in the query satisfies the property of independency (i.e., the condition can be expressed as a conjunction of conditions each involving a single attribute). We show that the overall time complexity of these specific algorithms is in O(W.log(W)), where W is the size of the data warehouse. Moreover, the case of analytic queries involving a having clause associated with a group-by clause is discussed in the context of our approach.