# A goal-directed implementation of query answering for hybrid MKNF knowledge bases

Ana Sofia Gomes, José Júlio Alferes, Terrance Swift

Research output: Contribution to journalArticle

1 Citation (Scopus)

### Abstract

Ontologies and rules are usually loosely coupled in knowledge representation formalisms. In fact, ontologies use open-world reasoning, while the leading semantics for rules use non-monotonic, closed-world reasoning. One exception is the tightly coupled framework of Minimal Knowledge and Negation as Failure (MKNF), which allows statements about individuals to be jointly derived via entailment from ontology and inferences from rules. Nonetheless, the practical usefulness of MKNF has not always been clear, although recent work has formalized a general resolution-based method for querying MKNF when rules are taken to have the well-founded semantics, and the ontology is modeled by a general oracle. That work leaves open what algorithms should be used to relate the entailments of the ontology and the inferences of rules. In this paper we provide such algorithms, and describe the implementation of a query-driven system, CDF-Rules, for hybrid knowledge bases combining both (non-monotonic) rules under the well-founded semantics and a (monotonic) ontology, represented by the Coherent Description Framework Type-1 ( $\mathcal{ALCQ}$) theory.

Original language English 239-264 26 Theory and Practice of Logic Programming 14 2 https://doi.org/10.1017/S1471068412000439 Published - 2014

### Fingerprint

Negation as Failure
Knowledge Base
Ontology
Query
Well-founded Semantics
Semantics
Reasoning
Knowledge representation
Knowledge Representation
Knowledge
Monotonic
Exception
Closed

### Keywords

• description logics
• implementation
• knowledge representation
• well-founded semantics

### Cite this

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title = "A goal-directed implementation of query answering for hybrid MKNF knowledge bases",
abstract = "Ontologies and rules are usually loosely coupled in knowledge representation formalisms. In fact, ontologies use open-world reasoning, while the leading semantics for rules use non-monotonic, closed-world reasoning. One exception is the tightly coupled framework of Minimal Knowledge and Negation as Failure (MKNF), which allows statements about individuals to be jointly derived via entailment from ontology and inferences from rules. Nonetheless, the practical usefulness of MKNF has not always been clear, although recent work has formalized a general resolution-based method for querying MKNF when rules are taken to have the well-founded semantics, and the ontology is modeled by a general oracle. That work leaves open what algorithms should be used to relate the entailments of the ontology and the inferences of rules. In this paper we provide such algorithms, and describe the implementation of a query-driven system, CDF-Rules, for hybrid knowledge bases combining both (non-monotonic) rules under the well-founded semantics and a (monotonic) ontology, represented by the Coherent Description Framework Type-1 ( $\mathcal{ALCQ}$) theory.",
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A goal-directed implementation of query answering for hybrid MKNF knowledge bases. / Gomes, Ana Sofia; Alferes, José Júlio; Swift, Terrance.

In: Theory and Practice of Logic Programming, Vol. 14, No. 2, 2014, p. 239-264.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A goal-directed implementation of query answering for hybrid MKNF knowledge bases

AU - Gomes, Ana Sofia

AU - Alferes, José Júlio

AU - Swift, Terrance

PY - 2014

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AB - Ontologies and rules are usually loosely coupled in knowledge representation formalisms. In fact, ontologies use open-world reasoning, while the leading semantics for rules use non-monotonic, closed-world reasoning. One exception is the tightly coupled framework of Minimal Knowledge and Negation as Failure (MKNF), which allows statements about individuals to be jointly derived via entailment from ontology and inferences from rules. Nonetheless, the practical usefulness of MKNF has not always been clear, although recent work has formalized a general resolution-based method for querying MKNF when rules are taken to have the well-founded semantics, and the ontology is modeled by a general oracle. That work leaves open what algorithms should be used to relate the entailments of the ontology and the inferences of rules. In this paper we provide such algorithms, and describe the implementation of a query-driven system, CDF-Rules, for hybrid knowledge bases combining both (non-monotonic) rules under the well-founded semantics and a (monotonic) ontology, represented by the Coherent Description Framework Type-1 ( $\mathcal{ALCQ}$) theory.

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