Ph.D. Theses

Integrity Constraints for the Semantic Web: An OWL 2 Description Logic Extension

By Jiao Tao
Advisor: Deborah L. McGuinness
March 19, 2012

With the extensive applications of Semantic Web technologies, an increasing amount of data has been published and consumed on the Semantic Web. Given some instance data, one might wonder if the data is ready for use. To answer this question, some data validation mechanisms are needed to ensure the data correctness and integrity. While syntax and semantics validation is supported by existing tools, the Semantic Web still lacks integrity constraint (IC) support. The standardized knowledge representation language, i.e., Web Ontology Language (OWL), has a standard semantics, that adopts the Open World Assumptions (OWA) and the non-Unique Name Assumptions (nUNA). This standard semantics is typically suitable for the distributed knowledge representation scenarios on the Web, where the knowledge about the domain comes from distributed sources and complete knowledge about the domain cannot be assumed. But this standard semantics makes it difficult to use OWL for closed world integrity constraint validation purposes when the knowledge about some parts of the domain is complete. This is because closed world constraint validation requires the Closed World Assumptions (CWA) and the Unique Name Assumptions (UNA) which contrast with the OWA and the nUNA respectively.

In this thesis, we propose an OWL 2 Description Logic (DL) extension to support integrity constraints on the Semantic Web. With this approach, OWL can be used not only as a knowledge representation language for open world reasoning, but also as an integrity constraint language for closed world constraint validation. The main contributions of this thesis work are as follows:

An integrity constraint semantics for OWL 2 DL that adopts the CWA and the weak UNA thus interpreting OWL axioms as integrity constraints
A sound and complete solution to integrity constraint validation by reduction to conjunctive queries
A solution to explanation and repair of integrity constraint violations based on explanations of answers to conjunctive queries
A prototype implementation that we used to evaluate some relatively well published semantic web instance data from real applications: Wine, MLSO, CEDAR, BCODMO, Datagov.

This thesis work addresses an important aspect of data validation on the Semantic Web. It supports discovery and repair of defects in the instance data thus enabling quality improvement of Semantic Web data.

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