Querying Incomplete Data over Extended ER Schemata

TL;DR

This paper presents a method for answering conjunctive queries over incomplete data in an extended ER schema using query rewriting into recursive Datalog, addressing schema reasoning in data integration scenarios.

Contribution

It introduces a query answering algorithm for incomplete data in extended ER models, utilizing schema-based query rewriting into recursive Datalog.

Findings

Decidability of query answering in extended ER schemas.

Algorithm for rewriting queries into recursive Datalog.

Extensions to more general schema settings.

Abstract

Since Chen's Entity-Relationship (ER) model, conceptual modeling has been playing a fundamental role in relational data design. In this paper we consider an extended ER (EER) model enriched with cardinality constraints, disjointness assertions, and is-a relations among both entities and relationships. In this setting, we consider the case of incomplete data, which is likely to occur, for instance, when data from different sources are integrated. In such a context, we address the problem of providing correct answers to conjunctive queries by reasoning on the schema. Based on previous results about decidability of the problem, we provide a query answering algorithm that performs rewriting of the initial query into a recursive Datalog query encoding the information about the schema. We finally show extensions to more general settings. This paper will appear in the special issue of Theory and Practice of Logic Programming (TPLP) titled Logic Programming in Databases: From Datalog to Semantic-Web Rules.