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Developing Ontologies based on RDF-OWL Semantic Web languages (for information sharing & knowledge representation) : 2006-04-13 David George.

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Presentation on theme: "Developing Ontologies based on RDF-OWL Semantic Web languages (for information sharing & knowledge representation) : 2006-04-13 David George."— Presentation transcript:

1 Developing Ontologies based on RDF-OWL Semantic Web languages (for information sharing & knowledge representation) : David George

2 2 How do we share data, information & knowledge? Demonstrated in several dimensions: we share amongst people – using HTML, dynamically with DBs share between database systems – linking DBs:DBs between organisations – exchanging data via XML and XSL transforms. in searches – autonomous & collaborative intelligent software agents. but...sharing data requires understanding of the context of terms... “the semantics of data” using metadata. Hence Semantic Web would provide shared understanding using metadata vocabularies (using an ontological approach).

3 3 We have the Web: a Global Information Space Some current Web statistics Approx. 40m web sites? Circa billion pages? (Google) Semantic Web share 0.001% usable Semantic Web files % are Ontologies

4 4 Result: effective query (precision) compromised New Zealand Cook Example: Query about Cook discovering New Zealand?

5 5 What is the Semantic Web? A project aimed to make web pages machine understandable. “An extension of the current Web, … information given well-defined meaning, …enabling computers and people to work in co-operation” (Berners-Lee et al, 2001) A universal medium for information exchange; where Ontologies are viewed as a pivotal component in giving meaning or semantics. A solution based on “XML-based” RDF (Resource Description Framework) and OWL Ontology languages (W3C, 2004). Expected that Semantic Web will have a role in Web Services and Grid Computing.

6 6 Descriptions of Ontology Some definitions of Ontologies: “An ontology is an explicit [formal] specification of a [shared] conceptualisation” (Gruber, 1993, [Borst, 1997]) “A logical theory which gives an explicit, partial account of a conceptualisation” (Guarino & Giaretta, 1995) “Conceptualisation refers to abstract model,.. formal refers to machine-readable,.. and shared reflects notion that ontology captures consensual knowledge shared by the group” (Studer et al, 1998) Socrates & Aristotle BC - philosophy of being: “Onto”

7 7 Ontology Examples “Ontology” covers a range of things Term lists - Catalogues for on-line shopping e.g. Amazon. Dublin Core meta standards for the Web. Linguistic structures – e.g. Thesauri like WordNet. Informal hierarchies or Taxonomies e.g. Yahoo & DMOZ directories. Detailed formal classifications e.g. UNSPSC Formal subsumption hierarchies like Gene Ontology. OWL DL based ontologies Domain-independent or philosophically inspired: Cyc, Sowa, IEEE SUMO Glossaries & Data Dictionaries Thesauri & Taxonomies Formal Ontologies & Inferencing

8 8 Why develop Ontologies? Enables re-use of terms and relationships to avoid reinventing descriptions. Allows domain knowledge to be separated from operational information. Helps to manage the information explosion caused by the Web. Makes domain descriptions and assumptions explicit by defining: – Concepts – relationships and attributes of concepts – constraints on properties – Instances

9 9 What do we have at present? Well, we don’t yet have a Semantic Web!

10 10 But we do have HTML and XML!

11 11 Dept. of Computing mailto: uclan.ac.uk CM222 David George Name Room Subject Ontology HTML Document para Document tableheadertext HTML syntax describes layout Simply a presentation of content Good for humans; not for machines HTML syntax describes layout Simply a presentation of content Good for humans; not for machines

12 12 David mailto: uclan.ac.uk CM222George Ontology Dept. of Computing XML Document Object Model XML structures information not page. Nested elements in tree hierarchy. Uses syntax to differentiate data. Universal standard for data exchange. Good for machines (and humans). XML structures information not page. Nested elements in tree hierarchy. Uses syntax to differentiate data. Universal standard for data exchange. Good for machines (and humans). Improve the description for understanding?

13 13 How can Semantic Web languages improve our interpretation of information?

14 14 My Research Using Semantic Web technologies to demonstrate that RDF- based language and Ontology can be used to integrate and share information. Examining the way in which different Ontology structures can be developed and mapped together. Motivating example will relate to Geographical (or Cosmological) domain – some early work. Developed an interface to query an Ontology. Some of the following slides relate to these domain concepts.

15 15 Geographic Ontology Layers Water Utility relief pipelines rivers L.A. Planning settlements economic demographics

16 16 Cosmological Ontologies

17 17 RDF Building Block

18 18 W3C standard (2004) for content (resource) description. RDF is machine-processable; but not for humans, as we’ll see! RDF parser interpretes common structures to convey semantics. Built on subject, predicate, object triples [a statement] A statement may say: is For example: RDF (Resource Description Framework) RDF uses the URI references like for describing s, p, o “resources” Resources are anything that can be identified on the Web. RDF uses the URI references like for describing s, p, o “resources” Resources are anything that can be identified on the Web. subject objectpredicate

19 19 Previous RDF example represents a Directed Acyclic Graph (directed graph with no directed cycles v a tree) RDF Model statement triple (Subject, predicate, object) allows nodes to be linked across the Web, e.g. student URL and computing/semanticweb URL.

20 20 RDF nodes

21 21 RDF is useful for describing data. Basis for Ontology structures using OWL Web Ontology Language. RDF graphs form complex directed graphs of linked triples, across the Web. RDF nodes

22 22 Current WebSemantic Web? Semantics through more Metadata a a a a a a a a a a a a a a a a a a a a (Kiryakov et al, 2004)

23 23 Semantic (Shadow) Web a a a a a a

24 24 How do we define metadata? Data/Information described by Metadata specified by Vocabularies formalised by Semantic Web languages Vocabulary Ontology used by Terms Metadata described by Content Data

25 25 OWL (Web Ontology Language) RDF Schema layer rdfs:Resource rdf:Property rdfs:Class rdfs:subClassOf OWL Ontology layer owl:Highway owl:PopGroup owl:ObjectProperty owl:connectedTo rdf:type rdfs:Domainrdfs:Range owl:City owl:Motorway rdfs:subClassOf Instance layer Manchester M62 owl:connectedTo

26 26 Role of Ontology in a Semantic Web DB KB

27 27 Hierarchy of Ontologies Upper-level Ontology Domain-level Ontology Task-level Ontology Application-level Ontology Imprecise – Abstract - Generalised Precise – Real - Specialised Upper-level: domain independent, general concept terms and relationships like space, time, matter, objects and events. [Ontology classification (Guarino, 1998)] Generic domain concepts, e.g. medical, pharmaceutical, travel; Generic tasks like buying or selling. Generic domain concepts, e.g. medical, pharmaceutical, travel; Generic tasks like buying or selling. specialisations of both domain and task, e..g. flight travel by a specific travel organisation.

28 28 “Upper-level” Ontologies (Chandrasekaran et al., 1999) Can represent the “starting points” for a field of study. Required when working in large groups, i.e. generalisation is required to gain consensus on agreed terms

29 29 Mapping Ontology Levels Thing Object Process Abstract Concrete Physical Process Physical Process Information Object Information Object Information Process Information Process Physical Object Physical Object Upper level Solar Physics Solar Physics Astromomy Planetary Exploration Planetary Exploration Cosmology Nuclear Fusion Nuclear Fusion Celestial Mechanics Celestial Mechanics Stellar Systems Stellar Systems Domain Manned Exploration Manned Exploration Galaxy Systems Galaxy Systems Planetary Characteristics Planetary Characteristics Solar System Solar System Planetary System Planetary System Sun Cosmic Microwaves Cosmic Microwaves Application

30 30 Mapping Geographical Layers (1)

31 31 Mapping Geographical Layers (2)

32 32 Ontology Mapping Ontology A, B, C, D Top-level Ontology A, B Ontology C, D Ontology AOntology B Ontology COntology D One-to-one mapping Ontology AOntology B Ontology COntology D Ontology A, B, C, D Shared Ontology Ontology DOntology BOntology AOntology C Clustered Ontologies Potentially many translating functions Complexity, scalability & maintenance No consensus issues Potentially many translating functions Complexity, scalability & maintenance No consensus issues Potential consensus problems in agreeing a standard between many users Resource ontologies are clustered on the basis of similarity. General concepts are shared at a higher level. Flexible and scalable Resource ontologies are clustered on the basis of similarity. General concepts are shared at a higher level. Flexible and scalable

33 Importing Ontology Structures

34 OWL ontology imports

35 35 Complexity in mapping Equivalence Different specifications of descriptions of relationships, when importing ontologies, will produce differing degrees of mappings, e.g. using equivalence, disjoint, and sub-class relations. This can superimpose additional complexity, for example recursive relations in equivalence.

36 36 OWL Web Ontology Language Three species of OWL: –OWL Lite – class, object & property terms, inc. inverse, transitive, equivalence, difference. –OWL DL – greater expressivity. inc. disjoint, min/max cardinality, union, complement, intersection complex but computationally decideable. –OWL Full – most expressive but computationally problematic, e.g. answers not in finite time. OWL based on “Open World Assumption” (OWA): (If not exists, will say NO only if can prove false). DBs based on “Closed World Assumption” (CWA): (If not exists, will say NO).

37 37 Ref: C,D = Class, I = Individual, R = Restriction OWL ConstructorProtégé-OWLExampleMeaning intersectionOf C ⊓ DPerson ⊓ Employee AND unionOf C ⊔ DMale ⊔ Female OR complementOf¬C¬MaleNOT oneOf{x y z}{Fiat BMW Ford}the set of someValuesFrom∃ R C∃ hasVehicle CarSOME (from) allValuesFrom∀ R C∀ hasVehicle CarONLY (from) minCardinalityR ≥ NhasVehicle ≥ 3MIN maxCardinalityR ≤ NhasVehicle ≤ 3MAX cardinalityR = NhasVehicle = 3EXACTLY hasValueR ∋ IhasVehicle ∋ FordHAS (specific indiv.) Description Logic Expressions

38 38 OWL RDF/XML-based Ontology Graph 2E52N 3E52N

39 39 Specifying Descriptions & Constraints

40 40 Ontology Development

41 41 Methodology Cyc Method (Lenat & Guha, 1990) Uschold & King (1995) TOV Project (Gruninger & Fox, 1995) Methontology (Fernandez-Lopez et al, 1997) SWBP & Patterns (Rector, 2004)

42 42 Application-independent Modelling MDA (Model Driven architecture) using UML-based modelling (Miller and Mukerji, 2003) Generalisation or Super class Generalisation or Super class

43 43 Protégé OWL Ontology Editor (Knublauch, 2003)

44 44 Using Reasoners in Classification Before classification: a TreeAfter: a Directed Acyclic Graph (Rector, 2004)

45 45 Jena-based Ontology Query Interface (George, 2006)

46 46 References BERNERS-LEE, T., HENDLER, J. & LASSILA, O. (2001) The Semantic Web. Scientific American, 284(5), pp BORST, W. N. (1997) Construction of Engineering Ontologies for Knowledge Sharing and Reuse. Ph.D. Thesis, SIKS - Dutch Graduate School for Information and Knowledge Systems. CHANDRASEKARAN, B., JOSEPHSON, J. R. & BENJAMINS, V. R. (1999) What Are Ontologies, and Why Do We Need Them? IEEE Intelligent Systems, 14(1), pp GEORGE, D. (2006) Developing Ontologies based on RDF-OWL Semantic Web languages [online]. Available from: [Accessed 13 April 2006]. GRUBER, T. R. (1993) A Translation Approach to Portable Ontology Specifications. Knowledge Acquisition, 5(2), pp GUARINO, N. (1998) Formal Ontology and Information Systems. In: Proceedings of 1st International Conference on Formal Ontologies in Information Systems (FOIS'98). Trento, Italy, 6-8 June IOS Press, pp KNUBLAUCH, H. (2003) An AI tool for the real world - Knowledge modeling with Protégé [online]. JavaWorld. Available from: [Accessed 23 December 2004]. LASSILA, O. & MCGUINNESS, D. (2001) The Role of Frame-Based Representation on the Semantic Web [online]. Technical Report KSL-01-02, Knowledge Systems Laboratory, Stanford University, CA. Available from: [Accessed 12 July 2005]. LENAT, D. B. (1995) CYC: A Large-Scale Investment in Knowledge Infrastructure. Communications of the ACM, 38(11), pp MILLER, J. & MUKERJI, J. (2003) Model Driven Architecture [online]. Object Management Group, Inc. Available from: [Accessed 29 September 2005]. RECTOR, A., NOY, N., KNUBLAUCH, H., SCHREIBER, G. & MUSEN, M. (2004) Ontology Design Patterns and Problems: Practical Ontology Engineering using Protege-OWL [online]. Available from: tutorial-2004/ISWC-Tutorial-Best-Practice.pdf. [Accessed 2 November 2005]. STUDER, R., BENJAMINS, V. R. & D.FENSEL (1998) Knowledge Engineering: Principles and Methods. Data & Knowledge Engineering, 25(1-2), pp USCHOLD, M. F. & JASPER, R. J. (1999) A Framework for Understanding and Classifying Ontology Applications. In: Proceedings of Proceedings of the IJCAI-99 workshop on Ontologies and Problem-Solving Methods (KRR5). Stockholm, Sweden, August pp

47 47 Ontology Distinctions Information and data exchange Could simply be delivered by basic specification of classes, properties and instances. Knowledge Sharing Describing classes like City (constraints and restrictions) by using logical expressions such as via necessary and sufficient conditions e.g. ∀ hasBuilding.Cathedral.

48 48 Ontology Spectrum Glossaries & Data Dictionaries Thesauri & TaxonomiesFormal hierarchy & increasing expressivenessNo specific hierachy (Lassila & McGuinness, 2001, Uschold & Gruninger, 2004) Formal Ontologies Inferencing


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