Pal gov.tutorial4.session1 2.whatisontology

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  • 1. ‫أكاديمية الحكومة اإللكترونية الفلسطينية‬ The Palestinian eGovernment Academy www.egovacademy.psTutorial 4: Ontology Engineering & Lexical Semantics Session 1.2 What is an Ontology Dr. Mustafa Jarrar University of Birzeit mjarrar@birzeit.edu www.jarrar.info PalGov © 2011 1
  • 2. AboutThis tutorial is part of the PalGov project, funded by the TEMPUS IV program of theCommission of the European Communities, grant agreement 511159-TEMPUS-1-2010-1-PS-TEMPUS-JPHES. The project website: www.egovacademy.psProject Consortium: Birzeit University, Palestine University of Trento, Italy (Coordinator ) Palestine Polytechnic University, Palestine Vrije Universiteit Brussel, Belgium Palestine Technical University, Palestine Université de Savoie, France Ministry of Telecom and IT, Palestine University of Namur, Belgium Ministry of Interior, Palestine TrueTrust, UK Ministry of Local Government, PalestineCoordinator:Dr. Mustafa JarrarBirzeit University, P.O.Box 14- Birzeit, PalestineTelfax:+972 2 2982935 mjarrar@birzeit.eduPalGov © 2011 2
  • 3. © Copyright NotesEveryone is encouraged to use this material, or part of it, but shouldproperly cite the project (logo and website), and the author of that part.No part of this tutorial may be reproduced or modified in any form or byany means, without prior written permission from the project, who havethe full copyrights on the material. Attribution-NonCommercial-ShareAlike CC-BY-NC-SAThis license lets others remix, tweak, and build upon your work non-commercially, as long as they credit you and license their new creationsunder the identical terms. PalGov © 2011 3
  • 4. Tutorial Map Topic Time Session 1_1: The Need for Sharing Semantics 1.5 Session 1_2: What is an ontology 1.5 Intended Learning ObjectivesA: Knowledge and Understanding Session 2: Lab- Build a Population Ontology 3 4a1: Demonstrate knowledge of what is an ontology, Session 3: Lab- Build a BankCustomer Ontology 3 how it is built, and what it is used for. Session 4: Lab- Build a BankCustomer Ontology 3 4a2: Demonstrate knowledge of ontology engineering and evaluation. Session 5: Lab- Ontology Tools 3 4a3: Describe the difference between an ontology and a Session 6_1: Ontology Engineering Challenges 1.5 schema, and an ontology and a dictionary. Session 6_2: Ontology Double Articulation 1.5 4a4: Explain the concept of language ontologies, lexical semantics and multilingualism. Session 7: Lab - Build a Legal-Person Ontology 3B: Intellectual Skills Session 8_1: Ontology Modeling Challenges 1.5 4b1: Develop quality ontologies. Session 8_2: Stepwise Methodologies 1.5 4b2: Tackle ontology engineering challenges. 4b3: Develop multilingual ontologies. Session 9: Lab - Build a Legal-Person Ontology 3 4b4: Formulate quality glosses. Session 10: Zinnar – The Palestinian eGovernment 3C: Professional and Practical Skills Interoperability Framework 4c1: Use ontology tools. Session 11: Lab- Using Zinnar in web services 3 4c2: (Re)use existing Language ontologies. Session 12_1: Lexical Semantics and Multilingually 1.5D: General and Transferable Skills d1: Working with team. Session 12_2: WordNets 1.5 d2: Presenting and defending ideas. Session 13: ArabicOntology 3 d3: Use of creativity and innovation in problem solving. Session 14: Lab-Using Linguistic Ontologies 3 d4: Develop communication skills and logical reasoning abilities. Session 15: Lab-Using Linguistic Ontologies 3 PalGov © 2011 4
  • 5. Session ILOsThis session will help student to: 4a1: Demonstrate knowledge of what is an ontology, how it is built, and what it is used for. 4a3: Describe the difference between an ontology and a schema, and an ontology and a dictionary. PalGov © 2011 5
  • 6. Reading Material0) Everything in these slides1)Thomas R. Gruber: Toward Principles for the Design of Ontologies Used for Knowledge Sharing http://tomgruber.org/writing/onto-design.pdf2) Nicola Guarino: Formal Ontology and Information Systems http://www.loa- cnr.it/Papers/FOIS98.pdf PalGov © 2011 6
  • 7. What is an Ontology?In Philosophy Ontology as such is usually contrasted with Epistemology, which deals with the nature and sources of our knowledge [a.k.a. Theory of Knowledge]. Aristotle defined Ontology as the science of being as such: " unlike the special sciences, each of which investigates a class of beings and their determinations, Ontology regards all the species of being qua being (‫ )كينونات‬and the attributes (‫ )صفات‬which belong to it qua being" (Aristotle, Metaphysics, IV, 1). • It is the science of what is (in the universe) . • Ontos (that which exists) + logos (knowledge of) • Dates back to Artistotle • Quine, 1969: “To exist is to be the value of a quantified variable” (‫)األنطولوجيا: علم الوجود بما هو موجود‬  So, it is a science (branch of philosophy): Analytical Philosophy ‫الفلسفة التحليلية‬ PalGov © 2011 7
  • 8. What is an Ontology?In computer science – McCarthy (1980) calls “a list of things that exist” an ontology. – Gruber (1995): “an explicit specification of a conceptualization”. – Welty (later): “Description of the kinds of entities there are and how they are related”. – Some people refer to as a domain model or a conceptual model. – To simplify it: Once my grandmother asked me about my research, I said “ontology”, she said what it this? I said: “it is a dictionary that computers can understand”. She said, how? I said, the computer computes the meaning as it is represented in logic. Note that “ontology” here is not a new name for an old thing. PalGov © 2011 8
  • 9. What is an Ontology?• An ontology is ... – an explicit specification of a conceptualization [Gruber93] – a shared understanding of some domain of interest [Uschold,Gruninger96]• Some aspects and parameters: – a formal specification (reasoning and “execution”) – ... of a conceptualization of a domain (community) – ... of some part of world that is of interest (application)• Provides: – A common vocabulary of terms – Some specification of the meaning of the terms (semantics) – A shared “understanding” for people and machines PalGov © 2011 9
  • 10. What is an Ontology?In computer science Gruber (1995): “a explicit specification of a conceptualization”. Written in logic, as a set the set of objects and relations in a of axioms i.e. a theory domain. <Objects,Relations,Functions> Conceptualization a = <Objects, Relations, Functions> b d c e PalGov © 2011 10
  • 11. What is an Ontology?In computer science Gruber (1995): “a explicit specification of a conceptualization”. Written in logic, as a set the set of objects and relations in a of axioms i.e. a theory domain. <Objects,Relations,Functions> Conceptualization: The ontology is a set of axioms used Block {a, b, c, d, e} to specify this conceptualization:a On {<a,b>,<b,c>,<d,e>} x y On(x,y)  Above(x,y)b d Above {<a,b>,<b,c>,<d,e>} … Clear {<a>,<d>}c e Table {<c>,<e>} Hat {<b,a>,<c,b>,<e,d>} Sharing these axioms (i.e., ontology) means sharing the same understanding PalGov © 2011 11
  • 12. What is an Ontology?In computer science Gruber (1995): “a explicit specification of a conceptualization”. Written in logic, as a set the set of objects and relations in a of axioms i.e. a theory domain. <Objects,Relations,Functions> Conceptualization: Guarino’s:a d Block {a, b, c, d, e}  This change implies changing On {<a,b>,<b,c>,<d,e>} the conceptualization.b Above {<a,b>,<b,c>,<d,e>}  Do we need to change our Clear {<a>,<d>}c e conceptualization each time Table {<c>,<e>} there is some re- Hat {<b,a>,<c,b>,<e,d>} arrangements in the world?! PalGov © 2011 12
  • 13. What is an Ontology?In computer science Gruber (1995): “a explicit specification of a conceptualization”. Written in logic, as a set the set of objects and relations in a of axioms i.e. a theory domain. <Objects,Relations,Functions> Conceptualization: Block {a, b, c, d, e} Guarino’s:a d  this conceptualization is a state On {<a,b>,<b,c>,<d,e>}b of affairs (= one situation a Above {<a,b>,<b,c>,<d,e>} snapshot) of the domain. Clear {<a>,<d>}c e Table {<c>,<e>}  This definition of Hat {<b,a>,<c,b>,<e,d>} conceptualization has a problem. PalGov © 2011 13
  • 14. Guarino’s definition of a conceptualization independent of any specific interpretation, model, or situation,A conceptualization is an intensional semantic structure,which encodes the implicit rules constraining the structure of a piece ofreality  These should not be ordinary relations, but rather conceptual relations. Conceptualization: a [[Block]]D {a, b, c, d, e}  A relations has a b d [[On]]D {<a,b>,<b,c>,<d,e>} model. [[Above ]]D {<a,b>,<b,c>,<d,e>} (extensional interpretation). c e [[Clear ]]D {<a>,<d>} [[Table ]]D {<c>,<e>}  A conceptual relation has [[Hat ]]D {<b,a>,<c,b>,<e,d>} intended models. (Intensional interpretation). PalGov © 2011 14
  • 15. Guarino’s definition of a conceptualization independent of any specific interpretation, model, or situation,A conceptualization is an intensional semantic structure,which encodes the implicit rules constraining the structure of a piece ofreality Ordinary relations are defined on a domain D Conceptual relations are defined on a domain space <D, W>An Ontology is an artifact designed with the purpose of expressing theintended meaning of a (shared) vocabulary.• A shared vocabulary plus a specification (characterization) of itsintended meaning PalGov © 2011 15
  • 16. How can we formally describe the meaning of a vocabulary?Given the “Palestinian Government” domain.How can we formally describe the meaning of the vocabulary (citizen,company, salary, tax, car, land, etc.) in this domain?Example: Company = a type of legal person, registered to conductbusiness, and recognized by its registration number. There are two types ofcompanies: Shareholding Company and Partnership Companies.In logic: LegalPersonCompany ⊑ LegalPerson Conducts ⊓ Conduct.Business Business ⊓ Has.RegestrationNumber Company HasShareholdingCompany ⊑ Company Registration Number PartnershipCompany ⊑ Company Shareholding Partnership Company Company PalGov © 2011 16
  • 17. How can we formally describe the meaning of a vocabulary?  Notice that meaning/semantics of “Company” can be determined from its position in the diagram, i.e., it is relations with other concepts, and constraints.Example: Company = a type of legal person, registered to conductbusiness, and recognized by its registration number. There are two types ofcompanies: Shareholding Company and Partnership Companies.In logic: LegalPersonCompany ⊑ LegalPerson Conducts ⊓ Conduct.Business Business ⊓ Has.RegestrationNumber Company HasShareholdingCompany ⊑ Company Registration Number PartnershipCompany ⊑ Company Shareholding Partnership Company Company PalGov © 2011 17
  • 18. How can we formally describe the meaning of a vocabulary? • Ministries need such precision and formal definitions to exchange data meaningfully. • We may use ORM/ER/UML as a language to specify the meaning (i.e., semantics) of a domain, as a formal notations. OWL is the standard ontology language.  Thus, an ontology consists of Concepts, Relations between these concepts, and some Rules.  The most important relation is the subtype relation.In logic: LegalPersonCompany ⊑ LegalPerson Conducts ⊓ Conduct.Business Business ⊓ Has.RegestrationNumber Company HasShareholdingCompany ⊑ Company Registration Number PartnershipCompany ⊑ Company Shareholding Partnership Company Company PalGov © 2011 18
  • 19. Part of the LegalPerson Ontology, in Palestine  The meaning of each of these concepts can be determined from its position PalGov © 2011 19
  • 20. Ontology vs Conceptual data Schema • But can we say that an ontology is a conceptual schema? i.e., is it true that the Palestinian government ontology is a conceptual database schema covering all data elements in all government databases? The answer is No! Then what is the difference between an ontology and a schema? DB schema provides skeleton/structure to the data, not meaning. Although ontology provides structure to the data, but the meaning is the most important aspect.In logic: LegalPersonCompany ⊑ LegalPerson Conducts ⊓ Conduct.Business Business ⊓ Has.RegestrationNumber Company HasShareholdingCompany ⊑ Company Registration Number PartnershipCompany ⊑ Company Shareholding Partnership Company Company PalGov © 2011 20
  • 21. Is this an Ontology or a Data Schema? Address Has Person ⊑ HasAddress.String ⊓ hasEmailPerson Has Email In OWL <owl:Class rdf:ID=“Person" /> <owl:Class rdf:ID=“Address" /> <owl:Class rdf:ID=“email" /> <owl:DataProperty rdf:ID=“Has-Address"> <rdfs:domain rdf:resource="#Person" /> <rdfs:range rdf:resource="www.w3.org/2001/XMLSchema#string"/> </owl:ObjectProperty> <owl:DataProperty rdf:ID=“Has-Email"> <rdfs:domain rdf:resource="#Person" /> <rdfs:range rdf:resource="www.w3.org/2001/XMLSchema#string"/> </owl:ObjectProperty>  What makes and ontology an ontology, not a schema? PalGov © 2011 21
  • 22. Where is the meaning (example: What is X?) Educational Has Email Institution Has Address X Project participates-In/ Faculties Composed-Of / If you can be sure of what is X from its position, then its characteristics (i.e., relations with other concepts) are suitable for defining its meaning? Which of these characteristics are more distinguishing? (Intrinsic verse extrinsic characteristics)“An intrinsic property (‫ )الصفة الجوهرية‬is typically something inherent to an individual, notdependent on other individuals, such as having a heart or having a fingerprint. Extrinsicproperties (‫ )الصفات العرضية‬are not inherent, and they have a relational nature, like “being afriend of John”. Among these, there are some that are typically assigned by external agents oragencies, such as having a specific social security number, having a specific customer ID, oreven having a specific name.” [GW00] PalGov © 2011 22
  • 23. Where is the meaning (example: What is X?) Educational Has Email Institution Has Address X Project participates-In/ Faculties Composed-Of /• An ontology that doesn’t hold intrinsic properties is not a good ontology, it becomes a schema, with poor or no meaning.• Ideally, it should “...catch all and only the intended meaning” [Gangemi 04]• Notice that having all and only the intrinsic properties is : (i) very difficult to represent ,e.g. how to represent “person has brain”, (ii) such properties are not needed in IT applications, so why to have them.• Thus, it is not necessary that the intrinsic properties be explicitly captured in the ontology, but these properties must govern the way we think and build the ontology. PalGov © 2011 23
  • 24. Where is the meaning (example: What is X?) Educational Has Email Institution Has Address X Project participates-In/ Faculties Composed-Of /• Hence, you (as a knowledge engineer) should be smart when making choices, so to achieve a general but applicable ontology, and not to end with a schema.• The more a knowledge engineer is aware of ontology modeling challenges, the better his/her skills will be in building quality ontologies.There are some methodologies to guide you building quality ontologies) (Ontology Modeling Challenges and Methodologies will be discussed later) PalGov © 2011 24
  • 25. The Ontological Level [Guarino] Level Primitives Interpretation Main feature Logical Predicates, Arbitrary Formalization functionsEpistemological Structuring Arbitrary Structure relations Ontological Ontological Constrained Meaning relations Conceptual Conceptual Subjective Conceptualization relations Linguistic Linguistic Subjective Language terms dependence PalGov © 2011 25
  • 26. References1)Thomas R. Gruber: Toward Principles for the Design of Ontologies Used for Knowledge Sharing http://tomgruber.org/writing/onto-design.pdf2) Nicola Guarino: Formal Ontology and Information Systems http://www.loa-cnr.it/Papers/FOIS98.pdf PalGov © 2011 26