210:, of classes all of whose individuals are wholes under the same relation. Like identity, OntoClean does not require that the relation itself be specified, often it is enough to know that the relation exists. Intuitively, a class has unity if all its instances are the same type of whole, and is typically true of classes of natural objects. Non-unity, indicated by
196:. An instance of this class might be some amount of the material (this is only one possible meaning, of course), such that any (in fact, every) arbitrary subsection of the amount would be a different instance of the same class. By contrast, instances of the class Person are, typically, not decomposable in this fashion.
141:
by the triangle class here, e.g. the same triangle could be in many places at the same time. Someone else may have an ontology in which the triangle class has different identity criteria, such that different drawings are always different triangles, even if they are the same size. Identity criteria
51:
The notions
Guarino & Welty focused on were drawn from philosophical ontology. They were not after the seemingly endless arguments about what the right ontology of the universe is, but rather the techniques these philosophers use to analyze, support, and criticize each other's arguments. These
313:
Note that these are just examples — it is certainly possible to have an ontology in which Person is anti-rigid. Imagine an ontology of mystical beliefs, for example, in which an entity changes from Person to Spirit upon death. In order for the individual to be the same across this change, being a
105:
More importantly for ontology are questions of identity that expose the existence of, or at least the need to represent, other entities. Here the issue at stake is finding the conditions under which a proposed entity would be both the same and different. The classic example is an amount of clay
79:
The distinction between property and class is subtle, and probably not critical to understanding OntoClean, however this article, follows the OntoClean publications and consistently uses "property" according to its original meaning, and one can treat "property" and "class" as synonymous. Thus a
329:
Dependence is a varied notion. In the core OntoClean papers, Guarino & Welty used a kind of dependence that captures a meta-property of certain relational roles. A property is dependent if each instance of it implies the existence of another entity. The property
Student, for example, is
271:, usually represented by the class Person. For every entity that has this property, the property is essential. So at least one of the properties that has not changed about me when I shave my beard is that I am a person. These properties, that are essential to all their instances, are
133:. A sortal is a class all of whose instances are identified in the same way. In information systems, these criteria are often extrinsic, like a social security number or universally unique id, which is not interesting from an ontological point of view. Identity criteria should be
399:
Guarino, Nicola, and Chris Welty. 2000. Identity, Unity, and
Individuation: Towards a Formal Toolkit for Ontological Analysis. In W. Horn, ed., Proceedings of ECAI-2000: The European Conference on Artificial Intelligence. Amsterdam:IOS Press. Pp. 219–223. August,
39:
OntoClean was the first attempt to formalize notions of ontological analysis for information systems. The idea was to justify the kinds of decisions that experienced ontology builders make, and explain the common mistakes of the inexperienced.
88:
The basis of OntoClean are the domain-independent properties of classes, the OntoClean metaproperties: identity, unity, rigidity, and dependence. Later work by Welty & Andersen has added two more metaproperties: permanence and actuality.
376:
Guarino, Nicola, and Chris Welty. 2000. Ontological
Analysis of Taxonomic Relationships. In, Laender, A. and Storey, V., eds, Proceedings of ER-2000: The 19th International Conference on Conceptual Modeling. Springer-Verlag. October,
338:
constant dependence. The former accounts for dependence on specific entities, e.g. each person is dependent on having a particular brain. The latter accounts for the
Student/Teacher case, where any instance of Teacher will do.
97:
Identity is fundamental to ontology, and especially to information systems ontologies. Identity is well known in metaphysics and in database conceptual modeling. In the latter case, it is an accepted best practice to specify a
137:, they should help us and others understand what a class means. A triangle, for example, can be identified by the length of its three sides, or by two sides and an interior angle, etc. This says a lot about what is
330:
dependent, since to be a student there must be a teacher; for every instance of student there is at least one instance of teacher. In later work for this was noted to subsume two kinds of property dependence:
59:
does not appear in the literature until 2002. According to
Thompson-ISI, work on OntoClean was the most cited of academic papers on Ontology. OntoClean was important as it was the first formal methodology for
145:
Identity criteria and sortals are intuitively meant to account for the linguistic habit of associating identity with certain classes. In the classical statue and clay example, we naturally say "the same
122:. In conceptual modeling, it is understood that when such an ambiguity arises, one should treat it as two different entities to account for a situation where one changes and the other stays the same.
199:
For the purposes of OntoClean, wholes are individuals all of whose parts are related to each other, and only to each other, by some distinguished relation. This relation can be viewed as a
214:, is the meta-property of classes whose instances are not all wholes, or not all wholes by the same relation. A further and more useful refinement of non-unity is anti-unity, indicated by
241:
makes good sense when first considered, however it doesn't take long to see how considerations of time causes problems between most ontologies (especially semantic web ontologies) and
142:(and OntoClean, for that matter) do not tell you that one of these definitions of triangle is right or wrong, just that they are different and thus that the classes are different.
76:
to be a member of a class. For example, we say that instances of the Person class have the property of "being a person." In the semantic web, a property is a binary relation.
260:; an essential property (and, q.v. terminology above, properties are unary predicates) of an entity is a property that cannot change, and these are the properties for which
203:
relation. Mere sums have no such relation since any decomposition of a mere sum is connected to any larger sum, which is not one of its parts, by the same relation.
321:, which are particulars. The term rigid in OntoClean is meant to describe the instanceOf link between an individual and a rigid class — it cannot be broken.
245:. For example, I might have a beard on one day and shave it off the next, yet I am the same entity at both times. How is it possible for me to be the
465:
256:
There are many logical approaches to this classic dilemma (including simply ignoring it), the most common is to consider some properties to be
52:
techniques make very little, if any, commitment to a particular ontology, instead they expose what are often very subtle distinctions.
470:
342:
There are many other kinds of dependence, see and especially . It is an open problem to adapt them into the OntoClean framework.
55:
The ideas underlying OntoClean appeared first in the literature in a series of three papers published in 2000. The name
41:
261:
242:
238:
388:
Proceedings of EKAW-2000: The 12th
International Conference on Knowledge Engineering and Knowledge Management.
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holds. Other properties of an entity that can change are non-essential and cannot be involved in identity.
386:
Guarino, Nicola, and Chris Welty. 2000. A Formal
Ontology of Properties. In, Dieng, R., and Corby, O., eds,
192:, which are individuals whose boundaries are, in a sense, arbitrary. For example, consider the class
218:, the meta-property of classes all of whose instances are not wholes, such as classes of mere sums.
176:) is inherited down the class hierarchy, if a class is a sortal then all its subclasses are as well.
61:
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for rows in a table. If "two" rows have identical primary keys, they are considered the same row.
424:
318:
23:
based on formal, domain-independent properties of classes (the metaproperties) developed by
409:
Guarino, Nicola and Chris Welty. 2002. Evaluating
Ontological Decisions with OntoClean.
48:, said, "What you have done is reduce the amount of time I spend arguing with medics."
24:
459:
72:
In logic, a property is a unary predicate in intention, in other words a property is
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person must not be essential and furthermore must be changeable (i.e. anti-rigid).
154:", indicating that there are identity criteria that are peculiar to each class.
438:
267:
Some properties are essential to all their instances. Think of the property of
28:
64:, applying scientific principles to a field whose practice was mostly art.
45:
20:
450:
Simons, P., 1987, Parts: A Study in
Ontology, Oxford: Clarendon Press.
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are associated with, or carried by, some classes of entities, called
184:
There are certain properties that only hold of individuals that are
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Berlin:Springer LNCS Vol. 1937/2000. Pp. 97–112. October, 2000.
294:), which are properties that must be changeable. Think of
286:. An important specialization of non-rigid properties are
188:. In formal ontology, wholes are often distinguished from
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Rigidity should not be confused with Kripke's notion of
160:
is the first OntoClean metaproperty, indicated with the
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for non-sortals) on a class in the original notation.
114:
statue, is it the same entity? If so, how could it be
80:metaproperty is a property of a property or class.
439:Towards OntoClean 2.0: A framework for Rigidity
298:— all students must possibly not be students.
44:, during a debate at the KR-2002 conference in
106:that is shaped into a statue. If you use the
8:
310:) is inherited down the class hierarchy.
230:) are inherited down the class hierarchy.
361:) is inherited down the class hierarchy.
206:Unity is the metaproperty, indicated by
369:
425:"Emerging Research Fronts:Ontologies"
7:
282:, and properties that are not rigid
278:Rigid properties are designated by
345:Being dependent is indicated with
14:
413:45(2):61–65. New York:ACM Press
19:is a methodology for analyzing
466:Ontology (information science)
1:
118:? If not, how could it be
110:clay but reshape it into a
487:
437:Welty and Andersen, 2005.
411:Communications of the ACM.
471:Philosophical methodology
349:, being independent with
334:constant dependence and
201:generalized connection
62:ontology engineering
35:Overview and History
68:Note on terminology
319:Rigid Designators
127:identity criteria
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451:
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273:rigid properties
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296:being a student
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150:" or "the same
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5:
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269:being a person
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158:Being a sortal
125:In OntoClean,
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91:
85:
84:Metaproperties
82:
69:
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36:
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25:Nicola Guarino
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262:Leibniz's law
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239:Leibniz's law
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164:superscript (
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74:what it means
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290:properties (
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16:
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135:informative
100:primary key
42:Alan Rector
29:Chris Welty
460:Categories
423:Thompson.
365:References
325:Dependence
288:anti-rigid
249:if I have
21:ontologies
357:(but not
302:(but not
258:essential
226:(but not
190:mere sums
172:(but not
116:different
112:different
57:OntoClean
17:OntoClean
332:specific
234:Rigidity
139:intended
120:the same
93:Identity
46:Toulouse
336:generic
251:changed
131:sortals
186:wholes
152:statue
400:2000.
377:2000.
180:Unity
247:same
222:and
194:clay
148:clay
108:same
27:and
353:.
306:or
462::
359:−D
355:+D
351:−D
347:+D
308:+R
304:−R
300:~R
292:~R
284:−R
280:+R
275:.
253:?
228:−U
224:~U
220:+U
216:~U
212:−U
208:+U
174:−I
170:+I
166:−I
162:+I
31:.
441:.
427:.
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