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Description Logics
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| Definitions |
A description logic is:
a logic-based knowledge representation formalism for
modelling a domain in terms of concepts (classes), roles (properties
and relations) and individuals (instances of classes).
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| Introduction |
For many computer applications, it is often useful to have access to symbolic models of an application world described in terms of individuals (e.g., calculus100) that are grouped into classes (e.g., COURSE, TEACHER, STUDENT) and related to other individuals and classes of individuals by relationships (e.g., calculus100 taught_by TEACHER). This conceptual structuring of domain knowledge has led to development of a number of network-based object-orientated formalisms (e.g., frame-based systems, semantic networks, feature logics, type systems) that have been specifically used to structure and allow reasoning over medical domain knowledge.
At their most basic, Description Logics employ a similar structuring of domain knowledge. Two main features of Description Logics justify their development:
- Description Logics are subsets of first order logic, and so can be viewed as providing a semantics for many network-based object-orientated formalisms. They serve to disambiguate imprecise representations that these formalisms permit. For example, what precisely is the meaning of the description FROG HasColour GREEN? - every frog is just green? every frog is also green? there is a frog which is just green?
- Description Logics are the most expressive decidable logics with classical semantics, and "good" reasoning procedures (especially when reasoning over large bodies of knowledge). This latter feature has been achieved after considerable research into the trade-off between the expressivity of first order logic formalisms and the tractability of implementing such formalisms for practical and usable representation of, and reasoning over, large bodies of domain knowledge.
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| Application in Medicine |
Description Logics and related formalisms are being applied in at least five application areas in medical informatics:
- terminology
- intelligent user interfaces
- decision support and semantic indexing
- language technology
- systems integration [Alan Rector, University of Manchester].
One of the most developed approaches in the application of Description Logics to medical
terminologies is provided by OpenGALEN. This foundation is
focused on the promotion and dissemination of terminology models, methods, architectures
and tools for clinical applications (developed under the EU GALEN programme).
A key activity of GALEN was the
development of the GRAIL Description Logic.
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| references - general |
| F. Baader, W. Nutt. Basic Description Logics. In the Description Logic Handbook, edited by F. Baader, D. Calvanese, D.L. McGuinness, D. Nardi, P.F. Patel-Schneider, Cambridge University Press, 2003, pages 47-100.
[CUP]
[]
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Book overview:
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Description Logics are a family of knowledge representation languages that have been studied extensively in Artificial Intelligence over the last two decades. They are embodied in several knowledge-based systems and are used to develop various real-life applications. The Description Logic Handbook provides a thorough account of the subject, covering all aspects of research in this field, namely: theory, implementation, and applications. Its appeal will be broad, ranging from more theoretically-oriented readers, to those with more practically-oriented interests who need a sound and modern understanding of knowledge representation systems based on Description Logics.
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Chapter introduction:
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This Introduction presents the main motivations for the development of Description Logics (DL) as a formalism for representing knowledge, as well as some important basic notions underlying all systems that have been created in the DL tradition. In addition, we provide the reader with an overview of the entire book and some guidelines for reading it. We first address the relationship between Description Logics and earlier semantic network and frame systems, which represent the original heritage of the field. We delve into some of the key problems encountered with the older efforts. Subsequently, we introduce the basic features of Description Logic languages and related reasoning techniques. Description Logic languages are then viewed as the core of knowledge representation systems, considering both the structure of a DL knowledge base and its associated reasoning services. The development of some implemented knowledge representation systems based on Description Logics and the rst applications built with such systems are then reviewed. Finally, we address the relationship of Description Logics to other fields of Computer Science. We also discuss some extensions of the basic representation language machinery; these include features proposed for incorporation in the formalism that originally arose in implemented systems, and features proposed to cope with the needs of certain application domains.
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Rector A. Modularisation of Domain Ontologies Implemented in Description Logics and related formalisms including OWL. Proc. K-CAP (Knowledge Capture) 2003
[]
[U Manchester]
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Modularity is a key requirement for large ontologies in order to achieve re-use, maintainability, and evolution. Mechanisms for 'normalisation' to achieve analogous aims are standard for databases. However, no similar notion of normalisation has yet emerged for ontologies. This paper proposes initial criteria for a two-step normalisation of ontologies implemented using OWL or related DL based formalisms. For the first - "ontological normalisation" - we accept Welty and Guarino's analysis. For the second - "implementation normalisation" - we propose an approach based on decomposing ("untangling") the ontology into independent disjoint skeleton taxonomies restricted to be simple trees, which can then be recombined using definitions and axioms to represent the relationships between them explicitly.
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| Baader F, Horrocks I, Sattler U. Description logics. In: Staab S, Studer R (Eds.). Handbook on Ontologies.
Series : International Handbooks on Information Systems. Pages 3-28.
Springer
2004. ISBN: 3-540-40834-7
[U Manchester]
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The vision of a Semantic Web has recently drawn consider-
able attention, both from academia and industry. Description logics are
often named as one of the tools that can support the Semantic Web and
thus help to make this vision reality.
In this paper, we describe what description logics are and what they can
do for the Semantic Web. Descriptions logics are very useful for defining,
integrating, and maintaining ontologies, which provide the Semantic Web
with a common understanding of the basic semantic concepts used to
annotate Web pages. We also argue that, without the last decade of basic
research in this area, description logics could not play such an important
role in this domain.
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| References: description logics in medicine |
| Rector A. Medical Informatics. Chapter 13 of the Description Logic Handbook, edited by F. Baader, D. Calvanese, D.L. McGuinness, D. Nardi, P.F. Patel-Schneider, Cambridge University Press, 2003, pages 406-426.
[CUP]
[U Roma]
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"
Description logics and related formalisms are being applied in at least five applications in medical informatics---terminology, intelligent user interfaces, decision support and semantic indexing, language technology, and systems integration. Important issues include size, complexity, connectivity, and the wide range of granularity required---medical terminologies require on the order of 250,000 concepts, some involving a dozen or more conjuncts with deep nesting; the nature of anatomy and physiology is that everything connects to everything else; and notions to be represented range from psychology to molecular biology. Technical issues for expressivity have focused on problems of part-whole relations and the need to provide ``frame-like'' functionality---i.e., the ability to determine efficiently what can sensibly be said about any particular concept and means of handling at least limited cases of defaults with exceptions. There are also significant problems with ``semantic normalisation'' and ``clinical pragmatics'' because understanding medical notions often depends on implicit knowledge and some notions defy easy logical formulation. The two best known efforts---OpenGALEN and SNOMED-RT---both use idiosyncratic description logics with generally limited expressivity but specialised extensions to cope with issues around part-whole and other transitive relations. There is also a conflict between the needs for re-use and the requirement for easy understandability by domain expert authors. OpenGALEN has coped with this conflict by introducing a layered architecture with a high level ``Intermediate Representation'' which insulates authors from the details of the description logic which is treated as an ``assembly language'' rather than the primary medium for expressing the ontology.
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Cornet R, Abu-Hanna A.
Description logic-based methods for auditing frame-based medical terminological systems.
Artif Intell Med. 2005 Jul;34(3):201-17.
[PubMed]
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OBJECTIVE: Medical terminological systems (TSs) play an increasingly important role in health care by supporting recording, retrieval and analysis of patient information. As the size and complexity of TSs are growing, the need arises for means to audit them, i.e. verify and maintain (logical) consistency and (semantic) correctness of their contents. This is not only important for the management of TSs but also for providing their users with confidence about the reliability of their contents. Formal methods have the potential to play an important role in the audit of TSs, although there are few empirical studies to assess the benefits of using these methods. METHODS AND MATERIAL: In this paper we propose a method based on description logics (DLs) for the audit of TSs. This method is based on the migration of the medical TS from a frame-based representation to a DL-based one. Our method is characterized by a process in which initially stringent assumptions are made about concept definitions. The assumptions allow the detection of concepts and relations that might comprise a source of logical inconsistency. If the assumptions hold then definitions are to be altered to eliminate the inconsistency, otherwise the assumptions are revised. RESULTS: In order to demonstrate the utility of the approach in a real-world case study we audit a TS in the intensive care domain and discuss decisions pertaining to building DL-based representations. This case study demonstrates that certain types of inconsistencies can indeed be detected by applying the method to a medical terminological system. CONCLUSION: The added value of the method described in this paper is that it provides a means to evaluate the compliance to a number of common modeling principles in a formal manner. The proposed method reveals potential modeling inconsistencies, helping to audit and (if possible) improve the medical TS. In this way, it contributes to providing confidence in the contents of the terminological system.
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| Cornet R, Abu-Hanna A.
Usability of expressive description logics--a case study in UMLS.
Proc AMIA Symp. 2002;:180-4.
[PubMed]
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Research in (medical) terminological knowledge representation is showing an increased interest in the family of Description Logics (DLs), as they allow for automatic reasoning. This interest is driven by an increase in demands on the quality of and reasoning ability with medical terminological knowledge. Recent advances in Computer Science have demonstrated the computational decidability and empirical tractability of quite expressive DLs. The question arises whether this expressivity is usable and useful. This paper motivates and describes an exploratory study to address this question by examining the surplus value of individual DL constructors based on an investigation of UMLS terms. Our study indicates that the disjunction and negation operators comprise very valuable extensions to current DLs. The impact of formalization depends on the involved semantic type; "Injury and Poisoning" is one of the semantic types in which a large portion of concepts will benefit from the extension.
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| links |
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| acknowledgements |
| Sanjay Modgil, Cancer Research UK. |
| page history |
Entry on OpenClinical (draft v0.1): 01 October 2004
Last main update: 18 October 2004 |
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Definitions