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Lecture Notes <br />University of Birzeit<br />2nd Semester, 2010<br />Advanced Artificial Intelligence (SCOM7341)<br />On...
Reading Material<br />0) Everything in these slides<br />1)Thomas R. Gruber: Toward Principles for the Design of Ontologie...
What is Ontology?<br />In Philosophy<br />Ontology as such is usually contrasted with Epistemology, which deals with the n...
What is Ontology?<br />In computer science<br /><ul><li>Gruber (1995): “a explicit specification of a conceptualization”.<...
What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the...
What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the...
do we need to change our conceptualization each time there is some re- arrangements in the world?!</li></ul>Conceptualizat...
What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the...
This definition of conceptualization has a problem.</li></ul>a<br />d<br />b<br />c<br />e<br />
Guarino’s definition of a conceptualization<br />independent of any specific interpretation, model, or situation,<br />A c...
A relations has a model.</li></ul>(extensional interpretation).<br /><ul><li>A conceptual relation has intended models.</l...
Guarino’s definition of a conceptualization<br />independent of any specific interpretation, model, or situation,<br />A c...
Ontologies vs. Conceptual Schemas<br />Conceptual schemas<br />Often not accessible at run time<br />Usually no formal sem...
Ontologies vs. Knowledge Bases<br />Knowledge base<br />   – Assertional component<br />• reflectsspecific (epistemic) sta...
Ontologies vs. classifications<br />• Classifications focus on:<br />– access, based on pre-determined criteria<br />(enco...
Is this an Ontology or a Data Schema?<br />Address<br />Has<br />Person ⊑ HasAddress.String<br /> ⊓ hasEmail<br />Person<b...
Educational Institution<br />Project<br />participates-In/<br />Faculties<br />Composed-Of/<br /><ul><li> Which of these c...
Educational Institution<br />Project<br />participates-In/<br />Faculties<br />Composed-Of/<br />Example, What is X? where...
(Some) Ontology Engineering Challenges <br />Ontology Application Dependence<br />Ontologies are supposed to capture knowl...
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Jarrar.lecture notes.aai.2011s.ontology part2_whatisontology

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Jarrar.lecture notes.aai.2011s.ontology part2_whatisontology

  1. 1. Lecture Notes <br />University of Birzeit<br />2nd Semester, 2010<br />Advanced Artificial Intelligence (SCOM7341)<br />Ontology<br />Part 2 What is Ontology?<br />Dr. Mustafa Jarrar<br />mjarrar@birzeit.eduwww.jarrar.info<br />University of Birzeit<br />
  2. 2. Reading Material<br />0) Everything in these slides<br />1)Thomas R. Gruber: Toward Principles for the Design of Ontologies Used for Knowledge Sharing http://tomgruber.org/writing/onto-design.pdf<br />2)Nicola Guarino: Formal Ontology and Information Systems http://www.loa-cnr.it/Papers/FOIS98.pdf<br />
  3. 3. What is Ontology?<br />In Philosophy<br />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 (كينونات) and the attributes (صفات) which belong to it qua being" (Aristotle, Metaphysics, IV, 1). <br />It is the science of what is (in the universe) .<br />Ontos (that which exists) + logos (knowledge of) <br />Dates back to Artistotle<br />Quine, 1969: “To exist is to be the value of a quantified variable”<br /> So, it is a science (branch of philosophy). <br />
  4. 4. What is Ontology?<br />In computer science<br /><ul><li>Gruber (1995): “a explicit specification of a conceptualization”.</li></ul>the set of objects and relations in a domain<br /><Objects, Relations, Functions><br />Written in logic, as a set of axioms i.e. a theory<br />Conceptualization<br />= <Objects, Relations, Functions><br />a<br />b<br />d<br />c<br />e<br />
  5. 5. What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the set of objects and relations in a domain. <Objects,Relations,Functions><br />Written in logic, as a set of axioms i.e. a theory<br />Conceptualization:<br />Block {a, b, c, d, e}<br />On {<a,b>,<b,c>,<d,e>}<br />Above {<a,b>,<b,c>,<d,e>}<br />Clear {<a>,<d>}<br />Table {<c>,<e>}<br />Hat {<b,a>,<c,b>,<e,d>}<br />The ontology is a set of axioms used to specify this conceptualization:<br /> x y On(x,y)  Above(x,y)<br /> …<br />a<br />b<br />d<br />c<br />e<br />Sharing these axioms (i.e., ontology) means sharing the same understanding<br />
  6. 6. What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the set of objects and relations in a domain. <Objects,Relations,Functions><br />Written in logic, as a set of axioms i.e. a theory<br />Guarino’s: <br /><ul><li>this change implies changing the conceptualization.
  7. 7. do we need to change our conceptualization each time there is some re- arrangements in the world?!</li></ul>Conceptualization:<br />Block {a, b, c, d, e}<br />On {<a,b>,<b,c>,<d,e>}<br />Above {<a,b>,<b,c>,<d,e>}<br />Clear {<a>,<d>}<br />Table {<c>,<e>}<br />Hat {<b,a>,<c,b>,<e,d>}<br />a<br />d<br />b<br />c<br />e<br />
  8. 8. What is Ontology?<br />In computer science<br />Gruber (1995): “a explicit specification of a conceptualization”.<br />the set of objects and relations in a domain. <Objects,Relations,Functions><br />Written in logic, as a set of axioms i.e. a theory<br />Conceptualization:<br />Block {a, b, c, d, e}<br />On {<a,b>,<b,c>,<d,e>}<br />Above {<a,b>,<b,c>,<d,e>}<br />Clear {<a>,<d>}<br />Table {<c>,<e>}<br />Hat {<b,a>,<c,b>,<e,d>}<br />Guarino’s: <br /><ul><li>this conceptualization is a state of affairs (= one situation a snapshot) of the domain.
  9. 9. This definition of conceptualization has a problem.</li></ul>a<br />d<br />b<br />c<br />e<br />
  10. 10. Guarino’s definition of a conceptualization<br />independent of any specific interpretation, model, or situation,<br />A concetualization is an intensional semantic structure, which encodes the implicit rules constraining the structure of a piece of reality<br /><ul><li>These should not be ordinary relations, but rather conceptual relations.
  11. 11. A relations has a model.</li></ul>(extensional interpretation).<br /><ul><li>A conceptual relation has intended models.</li></ul>(Intensionalinterpretation).<br />Conceptualization:<br /> [[Block]]D{a, b, c, d, e}<br /> [[On]]D{<a,b>,<b,c>,<d,e>}<br /> [[Above ]]D {<a,b>,<b,c>,<d,e>}<br /> [[Clear ]]D{<a>,<d>}<br /> [[Table ]]D{<c>,<e>}<br />[[Hat ]]D{<b,a>,<c,b>,<e,d>}<br />a<br />b<br />d<br />c<br />e<br />
  12. 12. Guarino’s definition of a conceptualization<br />independent of any specific interpretation, model, or situation,<br />A concetualization is an intensional semantic structure, which encodes the implicit rules constraining the structure of a piece of reality<br />Ordinary relations are defined on a domain D:<br />Conceptual relations are defined on a domain space<D, W><br />An Ontology is an artifact designed with the purpose of expressing the intended meaning of a (shared) vocabulary.<br />• A shared vocabulary plus a specification (characterization) of its intended meaning<br />
  13. 13. Ontologies vs. Conceptual Schemas<br />Conceptual schemas<br />Often not accessible at run time<br />Usually no formal semantics<br />attribute values taken out of the UoD<br />constraints relevant for database update<br />Ontologies<br />Usually accessible at run time<br />formal semantics<br />attribute values first-class citizens<br />constraints relevant for intended meaning<br />
  14. 14. Ontologies vs. Knowledge Bases<br />Knowledge base<br /> – Assertional component<br />• reflectsspecific (epistemic) states of affairs<br />• designed for problem-solving<br /> – Terminological component (ontology)<br />• independent of particular states of affairs<br />• Designed to support terminological services<br />Ontological formulas are (assumed to be) necessarily true<br />
  15. 15. Ontologies vs. classifications<br />• Classifications focus on:<br />– access, based on pre-determined criteria<br />(encoded by syntactic keys)<br />• Ontologies focus on:<br />– Meaning of terms<br />– Nature and structure of a domain<br />
  16. 16. Is this an Ontology or a Data Schema?<br />Address<br />Has<br />Person ⊑ HasAddress.String<br /> ⊓ hasEmail<br />Person<br />Email<br />Has<br />In OWL<br /><owl:Class rdf:ID=“Person" /><br /><owl:Class rdf:ID=“Address" /><br /><owl:Class rdf:ID=“email" /><br /><owl:DataProperty rdf:ID=“Has-Address"><br /> <rdfs:domain rdf:resource="#Person" /><br /> <rdfs:range rdf:resource="www.w3.org/2001/XMLSchema#string"/><br /></owl:ObjectProperty><br /><owl:DataProperty rdf:ID=“Has-Email"><br /> <rdfs:domain rdf:resource="#Person" /><br /><rdfs:range rdf:resource="www.w3.org/2001/XMLSchema#string"/><br /></owl:ObjectProperty><br /> What makes and ontology an ontology<br />
  17. 17. Educational Institution<br />Project<br />participates-In/<br />Faculties<br />Composed-Of/<br /><ul><li> Which of these characteristics are more distinguishing? </li></ul>(Intrinsic verse extrinsic characteristics)<br />Example, What is X? where is the meaning/semantics?<br />Email<br />Has<br />Address<br />Has<br />X<br />“An intrinsic property (الصفات الجوهرية) is typically something inherent to an individual, not dependent on other individuals, such as having a heart or having a fingerprint. Extrinsic properties (الصفات العرضية) are not inherent, and they have a relational nature, like “being a friend of John”. Among these, there are some that are typically assigned by external agents or agencies, such as having a specific social security number, having a specific customer i.d., even having a specific name.”<br />
  18. 18. Educational Institution<br />Project<br />participates-In/<br />Faculties<br />Composed-Of/<br />Example, What is X? where is the meaning/semantics?<br />Email<br />Has<br />Address<br />Has<br />X<br />An ontology that doesn’t hold intrinsic properties is not a good ontology, otherwise where is the semantics/real-meaning? <br />(Ideally, it should“...catch all and only the intended meaning” [Gangemi 04])<br />Notice that 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.<br />
  19. 19. (Some) Ontology Engineering Challenges <br />Ontology Application Dependence<br />Ontologies are supposed to capture knowledge at the domain level independently of application requirements [G97] [GB99] [CJB99].<br />The problem is that when building an ontology, there will always be intended or expected usability requirements -“at hand”- which influence the independency level of ontology axioms. <br />Bylander and Chandrasekaran argued in [BC88] that:<br />“Representing knowledge for the purpose of solving some problem is strongly affected by the nature of the problem and the inference strategy to be applied to the problem.”<br />
  20. 20. (Some) Ontology Engineering Challenges <br />?<br />Libraries<br />Ontology Application Dependence<br />Usability perspectives lead to different (and sometimes conflicting) axiomatizations although these axiomatizations might agree at the domain level.<br />Bookstores<br />
  21. 21. (Some) Ontology Engineering Challenges <br />?<br />Libraries<br />Ontology Application Dependence<br />Usability perspectives lead to different (and sometimes conflicting) axiomatizations although these axiomatizations might agree at the domain level.<br />Bookstores<br />Both are not ontologies, they are data schemes<br />
  22. 22. The Ontological Level<br />[Guarino]<br />

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