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    Pal gov.tutorial4.session8 1.ontologymodelingchallenges Pal gov.tutorial4.session8 1.ontologymodelingchallenges Presentation Transcript

    • ‫أكاديمية الحكومة اإللكترونية الفلسطينية‬ The Palestinian eGovernment Academy www.egovacademy.psTutorial 4: Ontology Engineering & Lexical Semantics Session 8.1 Ontology Modeling Challenges Dr. Mustafa Jarrar University of Birzeit mjarrar@birzeit.edu www.jarrar.info PalGov © 2011 1
    • 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
    • © 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
    • 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
    • Outline and Session ILOsThis session will help student to:4a2: Demonstrate knowledge of ontology engineering and evaluation.4b1: Develop quality ontologies.4b2: Tackle ontology engineering challenges. PalGov © 2011 5
    • ReadingGuarino, Nicola and Chris Welty. 2002. Evaluating Ontological Decisions withOntoClean. Communications of the ACM. 45(2):61-65. New York: ACM Press. http://www.loa.istc.cnr.it/Papers/CACM2002.pdf PalGov © 2011 6
    • Ontology Modeling• Building ontologies is still arcane art form.• One maybe a good ontology engineer, but he does not know why!• An ontology might be better than another, but it is difficult to know why!• We need a methodology to guide us not only on what kinds of ontological decisions we should make, but on how these decisions can be evaluated. OntoClean provides a set of modeling ―guidelines‖ in this direction, but it is still not meant to be a comprehensive methodology for the all ontology modeling phases. PalGov © 2011 7
    • OnToCleanA methodology for ontology-driven conceptual analysis, developedby: Nicola Guarino CNR Institute for Cognitive Sciences and Technologies, Laboratory for Applied Ontology (LOA) in Trento, Italy Chris Welty Research Scientist at the IBM T.J. Watson Research Center in New York. PalGov © 2011 8
    • Modeling mistakes • Many people misuse the subsumption relation, what they do is not subsumptions. • Which are correct/wrong here? Person Time Duration Educational Institute Student worker University Time Interval Person Birzeit University RoleStudent worker Female Male Faculty of Law PalGov © 2011 9
    • Modeling mistakes • Many people misuse the subsumption relation, what they do is not subsumptions. • Which are correct/wrong here? Person Educational Institute  How to know that your Time Duration modeling choices are right? Student worker  What makes your ontology better than my ontology? University Time Interval Person Birzeit University RoleStudent worker Female Male Faculty of Law PalGov © 2011 10
    • Subsumption (The Subtype Relation)• The subsumption (also called is-a relationship) forms a hierarchy – A subsumes B if all instances of B are necessarily instances of A – Attributes of a supertype are inherited by it subtypes along the hierarchy.• The subsumption relation is often misused – People are typically confuses the subtype relation with the part-of and instance-of relations, and types with roles. PalGov © 2011 11
    • Subsumption misused with Instantiation Mammal Species Mammal Species XIs AIs A SubtypeOf InstanceOf Human HumanIs A X InstanceOf Mustafa Mustafa Instances are sometimes confused with types! To distinguish between them you should ask what are the instances of ―Mustafa‖? Instances of ―Human‖? Instance of Species? Etc. How to distinguish between same/different instances of a type, two things are same entity (identity criteria)? PalGov © 2011 12
    • Subsumption misused with Part/Whole Car Car SubtypeOf X PartOf Engine EngineIt is often difficult for beginners in ontological analysis to distinguish between the part-of and thesubclass relation. This is due to the fact that subclass is analogous to subset, and a subset of aset is a part of it. This confusion can be overcomed when we realize the difference between theparts of a set and the parts of its members Among the essential properties of a car there are some functional properties, like being ableto accommodate people. An engine has also certain functional properties as essentialproperties, like being able to crank and generate a rotational force. Since, however, theessential properties of cars do not apply to engines, one cannot subsume the other. Theproper relationship here is part and subsumption is not part. [GW02]. PalGov © 2011 13
    • Subsumption misused with Disjunction Car Part Engine or Wheel or Seat SubtypeOf X SubtypeOf But this is still not an intuitive class Engine Better Car PartTo see how this is incorrect, rigidity analysis can be most useful. No instance of a car part isnecessarily a car part (we could take an engine from a car and put it in a boat, making it nolonger a car part but a boat part), so we have to make that class anti-rigid. The class engineitself is rigid, however, since we can’t imagine an entity that is an engine becoming a non-engine. Being an engine is essential to it. An anti-rigid class, such as car part, can notsubsume a rigid one, and so we have a conflict.This type of mistake is particularly common in object-oriented, where value restrictions are animportant part of modeling. These anti-rigid classes are created to satisfy a modeling need torepresent disjunction, for instance, ―any car part is either an engine, or a wheel, or a seat, …‖It should be clear that this is different from saying ―all engines are car parts,‖ since, in fact,they are not. Of course, most modeling systems do not provide for disjunction, so modelersbelieve they are justified using these tricks, but if the intention is to make meaning as clear aspossible then subsumption is not disjunction. [GW02] PalGov © 2011 14
    • Subsumption misused with Constitution  An instance of Water is Ocean Water an amount of waterSubtypeOf X PartOf Ocean  An instance of Ocean is the Water “the Atlantic Ocean,”  Oceans are made up of amounts of water PalGov © 2011 15
    • Subsumption misused with Polysemy • A term may have multiple meanings (Polysemy), • For example ―Table‖ means:  A piece of furniture having a smooth flat top that is usually supported by one or more vertical legs.  A set of data arranged in rows and columns Furniture Array PoliticalEntity GeographicArea SubtypeOf ? SubtypeOf SubtypeOf ? SubtypeOf Table Country A polysemous class might be placed below both meanings PalGov © 2011 16
    • OntoCleanOntoClean helps you to:• evaluate misuses of subsumption and inconsistent modeling choices.• provides a formal basis for why they’re wrong.• Focuses on taxonomy A subsumes B iff for all x, x instance of B implies x instance of A PalGov © 2011 17
    • OntoClean based on [Bechhofer]• Considers general properties – being an apple – being a table – being a person – being red• A Class is then the set of entities that exhibit a property in a possible world.• Members of the Class are instances of the property.• The terminology can be slightly confusing – These are not properties in the sense of OWL properties. PalGov © 2011 18
    • OntoClean based on [Bechhofer]• Metaproperties describe particular characteristics of the properties. • Essence • Rigidity • Identity • Unity• Associating metaproperties with properties (i.e. classes) helps characterize aspects of the properties.• Constraints on the metaproperties enforce restrictions on the taxonomy and help to highlight and evaluate the choices made. PalGov © 2011 19
    • Essence (‫)الجوهر‬• A property (i.e. class) is essential to an entity if it must hold for it. – Not just things that accidently happen to be true all the time. ‫تكون الصفة جوهرية لكينونة ما إذا كان إجبارية‬ .‫تكون الصفة غير جوهرية لكينونة ما إذا كانت عرضية، لوقت معين وليس طوال الوقت‬ PalGov © 2011 20
    • Rigidity )‫(صفة اللزوم‬• A rigid property is a property that is essential to all of its instances. ‫تكون الصفة الزمة إذا كانت جوهرية لجميع حامليها، مثل صفة إنسان ألن من يحمل هذه الصفة ال‬ .‫يمكنه التخلي عنها في أي وقت أو ظرف‬ – Every entity that can exhibit the property must do so. – Every entity that is a person must be a person – There are no entities that can be a person but aren’t.• An anti-rigid property is one that is never essential ‫تكون الصفة غير الزمة إذا لم تكن جوهرية لجميع حامليها، مثل صفة طالب ألن من يحمل هذه الصفة‬ .‫يمكنه التخلي عنها‬ – For example every instance of student isn’t necessarily a student - students may cease to be students at some point without ceasing to exist or changing their identity.• A semi-rigid property is one that is essential to some instances but not to others ‫تكون الصفة شبه الزمة إذا كانت جوهرية لبعض حامليها، مثل صفة قاسي فهي جوهرية للبعض مثل‬ .‫―مطرقة‖ وغير جوهرية للبعض اآلخر مثل ―اإلسفنج‖ القاسي‬ PalGov © 2011 21
    • Rigidity )‫(صفة اللزوم‬• A rigid property is a property that is essential to all of its instances. ‫تكون الصفة الزمة إذا كانت جوهرية لجميع حمليها، مثل صفة إنسان ألن من يحمل هذه الصفة ال‬ .‫يمكنه التخلي عنها في أي وقت أو ظرف‬ – Every entity that can exhibit the property must do so. – Every entity that is a person must be a person  Each concept in the Ontology should be – There are no entities that can be a person but aren’t. labeled with Rigid (+R) , Anti-rigid (-R), or• An anti-rigid Semi-rigid (~R). is never essential property is one that ‫تكون الصفة غير الزمة إذا لم تكن جوهرية لجميع حمليها، مثل صفة طالب ألن من يحمل هذه الصفة‬  As we will see‫يمكنه التخلي عنها‬ . later, these metaproperties impose – For example every instance of student isn’t necessarilywhich can be constraints on the subsumption relation, a student - students may used toto be students at someconsistency ofceasing to exist cease check the ontological point without taxonomic or changing their identity. links.• A semi-rigid propertyof thesethat is essential to some instances but not  One is one constraints is that anti-rigid properties to others cannot subsume rigid properties. Thus Student cannot ‫صفة قاسي فهي جوهرية للبعض مثل‬Person. ‫تكون الصفة شبه الزمة إذا كانت جوهرية لبعض‬ subsume ‫حمليها، مثل‬ .‫―مطرقة‖ وغير جوهرية للبعض اآلخر مثل ―اإلسفنج‖ القاسي‬ PalGov © 2011 22
    • Identity • Identity criteria allows us to recognize individual entities in the world. – Is that a dog?  Necessary and sufficient criteria in terms of definitions – Is that my dog? • Time Duration – One hour, two hours etc. • Time Interval – 11:00-12:00 on Tuesday 26th, 17:00-18:45 on Saturday 17th Time Duration Time Interval SubtypeOf X Component Of Time Duration Time IntervalWhen we say “all time intervals are time durations” we really mean “all time intervals have atime duration”; PalGov © 2011 23
    • Identity  Identity refers to the problem of being able to recognize individual entities in the world as being the same (or different).  Identity criteria are conditions used to determine equality (sufficient conditions) and that are entailed by equality (necessary conditions).  For example, how do we recognize a person we know as the same person even though they may have changed?  Thinking about concepts’ identities, while building an ontology help us avoid/discover mistakes.  For example: Time Duration Instances like: “One hour”, “two hours”, “one day” etc. SubtypeOf Time Interval Instances like: “1:00–2:00 next Tuesday”,“2:00–3:00 next Wednesday”, etc. since all Time Intervals are also Time Durations. PalGov © 2011 24
    • Identity According to the identity critera for time durations, two durations of the same length are the same duration. In other words, all one hour time durations are identical—they are the same duration and therefore there is only one ―one hour‖ time duration. According to the identity criteria for time intervals, two intervals occurring at the same time are the same, but two intervals occurring at different times, even if they are the same length, are different. Therefore, the two example intervals given would be different intervals, but the same duration. This creates a contradiction: if all instances of time interval are also instances of time duration (as implied by the subclass relationship), how can they be two instances under one class and a single instance under another? Time Duration Instances like: “One hour”, “two hours”, “one day” etc. SubtypeOf Time Interval Instances like: “1:00–2:00 next Tuesday”,“2:00–3:00 next Wednesday”, etc. since all Time Intervals are also Time Durations. PalGov © 2011 25
    • Identity When we say ―all time intervals are time durations‖ we really mean ―all time intervals have a time duration‖; the duration is a component of an interval, but it is not the interval itself. Therefore, we cannot model the relationship as subclass. Time Duration Time Interval SubtypeOf X Component Of Time Interval Time Duration X since all Time Intervals are also Time Durations. PalGov © 2011 26
    • Identity When we say ―all time intervals are time durations‖ we really mean ―all time intervals have a time duration‖; the duration is a component of an interval, but it is not the interval itself. Therefore, we cannot model the relationship as subclass. A property will inherit identity criteria from parents A property may also supply its own additional identity criteria Time Duration Time Interval SubtypeOf X Component Of Time Interval Time Duration X since all Time Intervals are also Time Durations. PalGov © 2011 27
    • Unity  Unity refers to the problem of describing the way the parts of an object are bound together.  Unity criteria identify whether or not a property is intended to describe whole objects.  For some classes, all their instances are wholes (like Car), for others none of their instances are wholes (like Oil).• A property carries unity if all its instances exhibit a common unity criterion (e.g., Ocean)• A property carries no unity if its instances are all wholes, but with different unity criteria (Legal Entity, as it includes companies and people• A property carries anti-unity if all of its instances are not necessarily whole PalGov © 2011 28
    • Unity  Thinking about concepts’ identities, while building an ontology helps us avoid/discover mistakes. For example: Instance is an amount of water, but it is not a whole, since it is Water not recognizable as an isolated entity. SubtypeOf Instances like the “Atlantic Ocean”, is recognizable as a Ocean single entityIf we claim that instances of the latter are not wholes, and instances of theformer always are, then we have a contradiction. Problems like thisagain stem from the ambiguity of natural language, oceans are not ―kindsof ―water‖, they are composed of water. PalGov © 2011 29
    • Unity  Thinking about concepts’ identities, while building an ontology helps us avoid/discover mistakes. For example: Water Water X SubtypeOf Composed Of Ocean OceanIf we claim that instances of the latter are not wholes, and instances of theformer always are, then we have a contradiction. Problems like thisagain stem from the ambiguity of natural language, oceans are not ―kindsof ―water‖, they are composed of water. PalGov © 2011 30
    • OntoClean’s support!• Recognizing identity and unity criteria is typically very difficult, and needs philosophical/analytical skill.• Well, of course good ontologies are not easy and need deep thinking!• These difficulties are not simplified much by OntoClean, but there is no better methodology!• More examples and practice help you become a good ontology modeler! …..  then your salary will be very high! ;-) PalGov © 2011 31
    • How to apply OntoClean? based on [Bechhofer] SubtypeOf Given two classes A and B, where B subsumes A, A the following rules must hold: B ?Rules1. If B is anti-rigid, then A must be anti-rigid2. If B carries an identity criterion, then A must carry the same criterion3. If B carries a unity criterion, then A must carry the same criterion4. If B has anti-unity, then A must also have anti-unity5. If B is externally dependent, then A must be• Analysis of a hierarchy using these rules can help identify problematic modeling choices.• Conceptual backbone of rigid properties PalGov © 2011 32
    • Summary based on [Bechhofer]• OntoClean helps a modeler to justify and analyze the choices made in defining a subsumption hierarchy.• Metaproperties : – Rigidity – Identity – Unity – Dependent• Application of constraints on metaproperties– Highlights potential inconsistencies in the modelling PalGov © 2011 33
    • ReferencesGuarino, Nicola and Chris Welty. 2002. Evaluating Ontological Decisions withOntoClean. Communications of the ACM. 45(2):61-65. New York: ACM Press.Sean Bechhofer: OntoClean. COMP30412. University of Manchesterhttp://www.cs.man.ac.uk/~seanb/teaching/COMP30412/OntoClean.pdf PalGov © 2011 34