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1PalGov © 2011 1PalGov © 2011
أكاديمية الحكومة اإللكترونية الفلسطينيةThe Palestinian eGovernment Academy
www.egovacademy.ps
Tutorial 4: Ontology Engineering & Lexical Semantics
Session 8.1
Ontology Modeling Challenges
Dr. Mustafa Jarrar
University of Birzeit
www.jarrar.info
2PalGov © 2011 2PalGov © 2011
About
This tutorial is part of the PalGov project, funded by the TEMPUS IV program of the
Commission of the European Communities, grant agreement 511159-TEMPUS-1-
2010-1-PS-TEMPUS-JPHES. The project website: www.egovacademy.ps
University of Trento, Italy
University of Namur, Belgium
Vrije Universiteit Brussel, Belgium
TrueTrust, UK
Birzeit University, Palestine
(Coordinator )
Palestine Polytechnic University, Palestine
Palestine Technical University, PalestineUniversité de Savoie, France
Ministry of Local Government, Palestine
Ministry of Telecom and IT, Palestine
Ministry of Interior, Palestine
Project Consortium:
Coordinator:
Dr. Mustafa Jarrar
Birzeit University, P.O.Box 14- Birzeit, Palestine
Telfax:+972 2 2982935 [email protected]
3PalGov © 2011 3PalGov © 2011
© Copyright Notes
Everyone is encouraged to use this material, or part of it, but should
properly 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 by
any means, without prior written permission from the project, who have
the full copyrights on the material.
Attribution-NonCommercial-ShareAlike
CC-BY-NC-SA
This license lets others remix, tweak, and build upon your work non-
commercially, as long as they credit you and license their new creations
under the identical terms.
4PalGov © 2011
Tutorial Map
Topic Time
Session 1_1: The Need for Sharing Semantics 1.5
Session 1_2: What is an ontology 1.5
Session 2: Lab- Build a Population Ontology 3
Session 3: Lab- Build a BankCustomer Ontology 3
Session 4: Lab- Build a BankCustomer Ontology 3
Session 5: Lab- Ontology Tools 3
Session 6_1: Ontology Engineering Challenges 1.5
Session 6_2: Ontology Double Articulation 1.5
Session 7: Lab - Build a Legal-Person Ontology 3
Session 8_1: Ontology Modeling Challenges 1.5
Session 8_2: Stepwise Methodologies 1.5
Session 9: Lab - Build a Legal-Person Ontology 3
Session 10: Zinnar – The Palestinian eGovernmentInteroperability Framework
3
Session 11: Lab- Using Zinnar in web services 3
Session 12_1: Lexical Semantics and Multilingually 1.5
Session 12_2: WordNets 1.5
Session 13: ArabicOntology 3
Session 14: Lab-Using Linguistic Ontologies 3
Session 15: Lab-Using Linguistic Ontologies 3
Intended Learning ObjectivesA: Knowledge and Understanding
4a1: Demonstrate knowledge of what is an ontology,
how it is built, and what it is used for.
4a2: Demonstrate knowledge of ontology engineering
and evaluation.
4a3: Describe the difference between an ontology and a
schema, and an ontology and a dictionary.
4a4: Explain the concept of language ontologies, lexical
semantics and multilingualism.
B: Intellectual Skills
4b1: Develop quality ontologies.
4b2: Tackle ontology engineering challenges.
4b3: Develop multilingual ontologies.
4b4: Formulate quality glosses.
C: Professional and Practical Skills
4c1: Use ontology tools.
4c2: (Re)use existing Language ontologies.
D: General and Transferable Skills
d1: Working with team.
d2: Presenting and defending ideas.
d3: Use of creativity and innovation in problem solving.
d4: Develop communication skills and logical reasoning
abilities.
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Outline and Session ILOs
This session will help student to:
4a2: Demonstrate knowledge of ontology engineering and
evaluation.
4b1: Develop quality ontologies.
4b2: Tackle ontology engineering challenges.
6PalGov © 2011 6PalGov © 2011
Reading
Guarino, Nicola and Chris Welty. 2002. Evaluating Ontological Decisions with
OntoClean. Communications of the ACM. 45(2):61-65. New York: ACM Press.
http://www.loa.istc.cnr.it/Papers/CACM2002.pdf
7PalGov © 2011 7PalGov © 2011
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.
8PalGov © 2011 8PalGov © 2011
OnToClean
Nicola Guarino
CNR Institute for Cognitive Sciences and Technologies,
Laboratory for Applied Ontology (LOA) in Trento, Italy
Research Scientist at the IBM T.J. Watson Research Center in
New York.
Chris Welty
A methodology for ontology-driven conceptual analysis, developed
by:
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Modeling mistakes
• Many people misuse the subsumption relation, what they do is not
subsumptions.
• Which are correct/wrong here?
Educational Institute
University
Faculty of Law
Birzeit University
Time Duration
Time Interval
Person
Student worker
Person
Female Male
Role
Student worker
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Modeling mistakes
• Many people misuse the subsumption relation, what they do is not
subsumptions.
• Which are correct/wrong here?
Educational Institute
University
Faculty of Law
Birzeit University
Time Duration
Time Interval
Person
Student worker
Person
Female Male
Role
Student worker
How to know that your modeling choices are right?
What makes your ontology better than my ontology?
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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.
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Subsumption misused with Instantiation
Mustafa
Human
Mammal Species
X
X
Mustafa
Human
Mammal Species
SubtypeOf
InstanceOf
InstanceOf
Is A
Is A
Is A
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)?
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Subsumption misused with Part/Whole
Engine
Car
SubtypeOf X PartOf
Engine
Car
It is often difficult for beginners in ontological analysis to distinguish between the part-of and the
subclass relation. This is due to the fact that subclass is analogous to subset, and a subset of a
set is a part of it. This confusion can be overcomed when we realize the difference between the
parts 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 essential
properties, like being able to crank and generate a rotational force. Since, however, the
essential properties of cars do not apply to engines, one cannot subsume the other. The
proper relationship here is part and subsumption is not part. [GW02].
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Subsumption misused with Disjunction
BetterEngine
Car Part
SubtypeOf X
This type of mistake is particularly common in object-oriented, where value restrictions are an
important part of modeling. These anti-rigid classes are created to satisfy a modeling need to
represent 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 modelers
believe they are justified using these tricks, but if the intention is to make meaning as clear as
possible then subsumption is not disjunction. [GW02]
Car Part
Engine or Wheel or Seat
SubtypeOf But this is still not an
intuitive class
To see how this is incorrect, rigidity analysis can be most useful. No instance of a car part is
necessarily a car part (we could take an engine from a car and put it in a boat, making it no
longer a car part but a boat part), so we have to make that class anti-rigid. The class engine
itself 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 not
subsume a rigid one, and so we have a conflict.
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Subsumption misused with Constitution
An instance of Ocean is the
“the Atlantic Ocean,”
Oceans are made up of
amounts of water
Ocean
Water
SubtypeOf
An instance of Water is
an amount of waterOcean
Water
PartOf
X
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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
Table
Furniture
SubtypeOf?
Array
SubtypeOf
A polysemous class might be placed below both meanings
Country
PoliticalEntity
SubtypeOf?
GeographicArea
SubtypeOf
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OntoClean
OntoClean 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
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OntoClean
• 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.
based on [Bechhofer]
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OntoClean
• 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.
based on [Bechhofer]
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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.
لكينونة ما إذا كان إجبارية جوهريةتكون الصفة
.لكينونة ما إذا كانت عرضية، لوقت معين وليس طوال الوقتغير جوهرية تكون الصفة
21PalGov © 2011 21PalGov © 2011
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
فهي جوهرية للبعض مثل قاسي مليها، مثل صفة اإذا كانت جوهرية لبعض ح شبه الزمةتكون الصفة
.القاسي‖ اإلسفنج―وغير جوهرية للبعض اآلخر مثل ‖ مطرقة―
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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
– 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 حمليها، 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
فهي جوهرية للبعض مثل قاسي إذا كانت جوهرية لبعض حمليها، مثل صفة شبه الزمةتكون الصفة
.القاسي‖ اإلسفنج―وغير جوهرية للبعض اآلخر مثل ‖ مطرقة―
Each concept in the Ontology should be
labeled with Rigid (+R) , Anti-rigid (-R), or
Semi-rigid (~R).
As we will see later, these metaproperties impose
constraints on the subsumption relation, which can be
used to check the ontological consistency of taxonomic
links.
One of these constraints is that anti-rigid properties
cannot subsume rigid properties. Thus Student cannot
subsume Person.
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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 Interval
Time Duration
SubtypeOf Component OfXTime Interval
Time Duration
When we say “all time intervals are time durations” we really mean “all time intervals have a
time duration”;
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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 Interval
Time Duration
SubtypeOfInstances like: “One hour”, “two hours”, “one day” etc.
Instances like: “1:00–2:00 next Tuesday”,“2:00–3:00 next Wednesday”, etc.
since all Time Intervals are also Time Durations.
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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 Interval
Time Duration
SubtypeOfInstances like: “One hour”, “two hours”, “one day” etc.
Instances like: “1:00–2:00 next Tuesday”,“2:00–3:00 next Wednesday”, etc.
since all Time Intervals are also Time Durations.
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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 Interval
Time Duration
SubtypeOf
since all Time Intervals are also Time Durations.
X Component Of
Time Interval
Time Duration
X
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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 Interval
Time Duration
SubtypeOf
since all Time Intervals are also Time Durations.
X Component Of
Time Interval
Time Duration
X
A property will inherit identity criteria from parents
A property may also supply its own additional identity criteria
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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
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Unity
Thinking about concepts’ identities, while building an ontology helps
us avoid/discover mistakes. For example:
Ocean
Water
SubtypeOf
Instance is an amount of water, but it is not a whole, since it is
not recognizable as an isolated entity.
Instances like the “Atlantic Ocean”, is recognizable as a
single entity
If we claim that instances of the latter are not wholes, and instances of the
former always are, then we have a contradiction. Problems like this
again stem from the ambiguity of natural language, oceans are not ―kinds
of ―water‖, they are composed of water.
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Unity
Thinking about concepts’ identities, while building an ontology helps
us avoid/discover mistakes. For example:
Ocean
Water
SubtypeOf
If we claim that instances of the latter are not wholes, and instances of the
former always are, then we have a contradiction. Problems like this
again stem from the ambiguity of natural language, oceans are not ―kinds
of ―water‖, they are composed of water.
XComposed Of
Water
Ocean
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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! ;-)
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How to apply OntoClean?
B
ASubtypeOf
?
1. If B is anti-rigid, then A must be anti-rigid
2. If B carries an identity criterion, then A must carry the same criterion
3. If B carries a unity criterion, then A must carry the same criterion
4. If B has anti-unity, then A must also have anti-unity
5. If B is externally dependent, then A must be
Given two classes A and B, where B subsumes A,
the following rules must hold:
• Analysis of a hierarchy using these rules can help identify problematic
modeling choices.
• Conceptual backbone of rigid properties
Rules
based on [Bechhofer]
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Summary
• 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
based on [Bechhofer]
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References
Guarino, Nicola and Chris Welty. 2002. Evaluating Ontological Decisions with
OntoClean. Communications of the ACM. 45(2):61-65. New York: ACM Press.
Sean Bechhofer: OntoClean. COMP30412. University of Manchester
http://www.cs.man.ac.uk/~seanb/teaching/COMP30412/OntoClean.pdf