ONTOarg: A decision support framework for ontology integration based on argumentation

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Abstract

Description Logic Programming (DLP) is a well-known approach to reason with Description Logic (DL) ontologies, translating them into the language of logic programming (LP). Even though DLP offers several advantages in terms of efficiency and reuse of existing logic programming tools (such as Prolog environments), a major hindrance of this approach is its limitation for reasoning in the presence of inconsistent ontologies. Recent research has led to the use of defeasible argumentation to model different DL reasoning capabilities when handling inconsistent ontologies, resulting in so-called δ-ontologies. In this article we present ONTOarg, a decision support framework for performing local-as-view integration of possibly inconsistent and incomplete ontologies in terms of Defeasible Logic Programming (DeLP). We show how to reason on Description Logics (DL) ontologies in an ontology integration system by performing a dialectical analysis in order to determine the membership of individuals to concepts. We present formal definitions of a framework for ontology integration of DL ontologies based on DeLP along with a case study and review some of the properties of the approach.

Highlights

► We show a method for performing local-as-view ontology integration in the presence of possible inconsistencies. ► The method is implemented in Defeasible Logic Programming. ► The method is apt for being implemented in the OWL language, which is the standard for Semantic Web applications. ► Some properties of the approach are presented. ► A framework is presented that could be used to implement an expert system, including a case study to show how the proposal works.

Introduction

The Semantic Web (Berners-Lee, Hendler, & Lassila, 2001) (SW) is a vision of the Web where agents can reason about resources whose meaning is assigned in terms of ontologies (Gruber, 1993). Within the Semantic Web, the OWL language has become the current standard for defining ontologies and its underlying semantics is based on Description Logics (DL) (Baader, Calvanese, McGuinness, Nardi, & Patel-Schneider, 2003), for which specialized reasoners exist (such as Racer (Haarslev & Möller, 2001) and Pellet (Parsia & Sirin, 2004)). In this context, Description Logic Programming (DLP) provides a practical approach to reason with DL ontologies, translating them into the language of logic programming (LP) (Grosof, Horrocks, Volz, & Decker, 2003). Although DLP offers several advantages in terms of efficiency and reuse of existing LP tools (such as Prolog environments), DLP is incapable of reasoning in the presence of inconsistent ontologies. Dealing with inconsistencies and potentially contradictory information is a common issue in semantic web reasoning. The semantic integration of potentially inconsistent information sources in the SW is complicated, as the knowledge engineer usually has no authority to correct foreign ontologies. Inconsistencies can also arise whenever the domains modeled are inherently inconsistent. Additionally, in many situations resources and their data are modeled in terms of ontologies whose terms can differ, so that the ontologies must be aligned to put their terms into mutual agreement (Klein, 2001).

Argumentation provides a sophisticated mechanism for the formalization of commonsense reasoning, which has found application and proven its importance in different areas of Artificial Intelligence (AI) such as legal systems, multi-agent systems, and decision support systems among others (see e.g. Bench-Capon and Dunne, 2007, Janjua and Hussain, 2012, Modgil et al., 2013, Rahwan and Simari, 2009). Intuitively, an argument can be thought of as a coherent set of statements that supports a claim. The ultimate acceptance of an argument will depend on a dialectical analysis of arguments in favor and against the claim (Rahwan & Simari, 2009). In the last decade, several frameworks for formalizing argumentative reasoning have been developed (also called generically Argumentation Systems), providing different knowledge representation and inference capabilities.

Recent research has led to the use of defeasible argumentation to model different DL reasoning capabilities when handling inconsistent ontologies, resulting in so-called δ-ontologies (Gómez, Chesñevar, & Simari, 2010). These special ontologies are based on Defeasible Logic Programming (DeLP) (García & Simari, 2004), a defeasible argumentation framework based on logic programming. In contrast with other approaches, δ-ontologies have the flexibility of allowing to assess defeasibly the membership of an individual to a concept description in the presence of a potential inconsistent ontology. However, this approach was intended for a single ontology, and fell short when dealing with different ontologies which have to be integrated in a single one. There are two kinds of ontology integration approaches, viz. global-as-view (GAV) and local-as-view (LAV) (Calvanese, Giacomo, & Lenzerini, 2001). When performing LAV integration, concepts of the local ontologies are mapped to queries over a global ontology.

In this article, we present ONTOarg, a decision support framework for modeling LAV ontology integration when the involved ontologies can be potentially inconsistent. The ontologies are expressed in the language of DL but their semantics is expressed in terms of DeLP. The alignments between the local and global ontologies are expressed as DL inclusion axioms that are also interpreted as DeLP sentences. As the ontologies are potentially inconsistent, a dialectical analysis is performed on the interpretation of both the ontologies and the mappings from the local to the global ontology. ONTOarg can be seen as a front-end expert system for the ontology engineers, which solves automatically the problem of alignments using an argumentative proof procedure.

The rest of this paper is structured as follows. In Section 2 we present the fundamentals of Description Logics and Defeasible Logic Programming. Section 3 recalls the δ-ontologies framework for reasoning with possibly inconsistent ontologies. In Section 4, we extend δ-ontologies for performing local-as-view integration of possibly inconsistent ontologies. Section 5 discusses some properties of the proposed approach. In Section 6 we compare our approach with related work. Finally Section 7 concludes the paper.

Section snippets

Description logics

Description Logics (DL) (Baader et al., 2003) are a family of knowledge representation formalisms based on the notions of concepts(unary predicates, classes) and roles (binary relations) that allow to build complex concepts and roles from atomic ones.

Let C, D stand for concepts, R for a role and a, b for individuals. Concept descriptions are built from concept names using the constructors conjunction (C  D), disjunction (C  D), complement (¬C), existential restriction (∃R.C), and value

Reasoning with inconsistent ontologies: δ-ontologies

In the presence of inconsistent ontologies, traditional DL reasoners (such as Racer (Haarslev & Möller, 2001)) issue an error message and stop further processing. Thus the burden of repairing the ontology (i.e., making it consistent) is on the knowledge engineer. However, the knowledge engineer is not always available and in some cases, such as when dealing with imported ontologies, he has neither the authority nor the expertise to correct the source of inconsistency. Therefore, we are

The ONTOarg framework: architecture

The notion of δ-ontology is powerful enough to reason defeasibly within a specific ontology with inconsistencies. However, a common problem for a knowledge engineer is associated with dealing with different δ-ontologies, which have to be unified or integrated in order to get a global understanding of the knowledge available in such ontologies, resulting in turn in the characterization of a global ontology. In the literature (Calvanese et al., 2001), the term ontology integration is associated

Some properties of the approach

We now introduce some properties of the proposed approach to ontology integration presented above. Notice that the validity of the properties is strongly related to DeLP reasoning dynamics.

Property 1

Let I=(G,S,M) be an ontology integration system. It cannot be the case that an individual a is a justified member of concepts C and ¬C simultaneously.

Proof

Suppose that both a is a justified member of both C and ¬C. Then it must be the case that there exist two warranted arguments A,C(a) and B,C(a). But this

Related work

Next we will review some recent research in reasoning with inconsistencies in ontologies, reasoning with ontologies in logic programming and recent advances in ontology integration, contrasting existing results with our approach.

Conclusions

We have presented an approach for performing local-as-view integration of Description Logic ontologies when these ontologies can be potentially inconsistent. We have adapted the notion of ontology integration system of Calvanese et al. (2001) for making it suitable for the δ-ontology framework, presenting both formal definitions and a case study.

For reasoning with an inconsistent ontology, it can be repaired manually by the knowledge engineer or automatically (e.g., using Belief Revision (

Acknowledgements

The research was funded by LACCIR Project 1211LAC004, by PIP CONICET Projects 112-200801-02798 and 112-200901-00863, and by Sec. Gral. de Ciencia y Tecnología, Universidad Nacional del Sur.

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