Adrian, (01)
To be fair, I was quoting from OWL documentation whose disucssion itself was
struggling with how to represent certain conceptualizations of the world (to
use Guarino's formulation of this) in the OWL formalism. In this process we
see some of the limitations of OWL-DL so this may indeed encourage us to move
to a more expressive formalism. So the discussion provides some value in that
direction as well as providing some ideas on a quality conceptualization for
part-whole. My suggestion is that this explicit discussion is useful to cover
with domain people help ontologists build ontologies. (02)
Gary Berg-Cross (03)
Ours is the age that is proud of machines that think and suspicious of men who
try to.
- H. Mumford Jones <http://www.quotationspage.com/quote/23570.html> (04)
________________________________ (05)
From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx on behalf of Adrian Walker
Sent: Sun 5/6/2007 3:43 PM
To: [ontolog-forum]
Subject: Re: [ontolog-forum] Finnegans Web (06)
Gary -- (07)
You wrote... (08)
"Several issues arise even from such a simple example. To begin with, the
representation using existential restrictions (i.e. owl:someValuesFrom) does
not clearly communicate all of the semantics we may want for car parts. For
example, a strict reading of the definition of the Crankcase class above is
that a crankcase is part of at least one engine. In point of fact, a crankcase
cannot be part of more than one engine. We may be tempted to add a cardinality
restriction (e.g. maxCardinality 1) on partOf to the definition of crankcase,
but this would be a mistake; since partOf is transitive, a crankcase is also
part of the car the engine is part of. Note also that OWL-DL does not allow
transitive properties to have any cardinality restrictions. In general it is
best to avoid placing restrictions (including range restrictions) on transitive
properties at all. (09)
Indeed, once one starts to represent real world things, it seems that they
often do not fit into the OWL "either transitive or not transitive" mold. (010)
So, the question then is whether OWL (1.1?) can usefully represent things that
are mostly transitive, but with niggling non-transitivities? (011)
Another example is "transitive over" as in [1,2]. Can that be represented in
recent versions of OWL? (012)
If the answer is No, then are we heading to a future in which OWL gradually
gets displaced by some more flexible approach? (013)
Cheers, -- Adrian (014)
Internet Business Logic
A Wiki for Executable Open Vocabulary English
Online at www.reengineeringllc.com <http://www.reengineeringllc.com/>
Shared use is free (015)
Adrian Walker
Reengineering (016)
[1] www.reengineeringllc.com/demo_agents/TransitiveOver1.agent (017)
[2] www.reengineeringllc.com/demo_agents/OwlResearchOnt.agent (018)
On 5/6/07, Gary Berg-Cross <gary.berg-cross@xxxxxxxx> wrote: (019)
Pat, (020)
In responding to Barry's comment on OBO: (021)
Barry>>The OBO Foundry has no objection to mappings a la alternative (3)
>(see http://obofoundry.org/cgi-bin/table.cgi?show=mappings
<https://mail.em-i.com/exchweb/bin/redir.asp?URL=http://obofoundry.org/cgi-bin/table.cgi?show=mappings
> ), though
>it has proved much more difficult in medicine than Pat here suggests.
>(3) may indeed be the right solution in the long run. But I believe
>that it can be successful only if different groups first follow
>alternative (2) in coherent fashion to create a solid basis for later
>>mappings. For alternative (3) surely gives ontology developers too
Barry >>little guidance as to what to do in the short run. (022)
You said, (023)
Pat>Perhaps. But what bothers me is this idea that ontology developers
need to be given 'guidance'. By who? By the ontology experts? But
there are no ontology-writing experts, really. We are all beginners
at this game. By philosophers? Excuse me while I laugh. By engineers?
Librarians? Software designers? Management experts? Nicola Guarino?
There are no end of people ready to give such advice, but none of
them have any real qualifications to do so; and all the advice given
Pat>is controversial. (024)
I wonder if this is a tad strong. Would you agree that advice that
shows up on representing
part-whole in OWL isn't helpful? For example, (025)
Simple part-whole relations in OWL Ontologies W3C Editor's Draft 11 Aug
2005 at (026)
http://www.w3.org/2001/sw/BestPractices/OEP/SimplePartWhole/ (027)
provides the following advice/guidance that seems to me to be of value: (028)
"In many applications, what is needed is not a list of all parts but
rather a list of the next level breakdown of parts, the "direct parts" of a
given entity. It is therfore often useful to use the property hierarchy to
define a subproperty <http://www.w3.org/TR/rdf-schema/#ch_subpropertyof> of
hasPart that is not transitive and links each subpart just to the next level.
For these examples we shall call this subproperty hasPart_directly. Note of
course that the mere idea of a "direct" part is subjective, one may invent
intermediate direct parts depending on numerous factors, or eliminate them. For
example, we may choose not to represent engine as a part of cars, but rather
represent all the components of engines as direct car parts. Grouping subparts
into larger parts may also be subjective, a common example is a flywheel in a
car, which can be viewed as an engine part or a transmission part in an
ontology that includes those classes. (029)
Choosing whether to use partOf or hasPart (030)
OWL supports inverse relations
<http://www.w3.org/TR/owl-ref/#inverseOf-def > , so we can define an inverse of
partOf, say hasPart. For any two individuals I1 and I2, if "I1 partOf I2" then
"I2 hasPart I1". However, care must be taken when using inverses in
restrictions on classes. To say that "All As are parts of some B" does not
imply that "All Bs have some As as parts", i.e. the restriction
(Class A partial restriction(partOf someValuesFrom(B))
does not imply
(Class B partial restriction(partOf someValuesFrom(A)) (031)
Therefore, if we want to say both that "all As are parts of some B" and
"all Bs have part some A", we have to assert each statement separately. Such
pairs of statements are sometimes called "reciprocals". " (032)
Later another issue is addressed and guidance provided when considering
parts of a car (engine, lights etc.): (033)
"Several issues arise even from such a simple example. To begin with,
the representation using existential restrictions (i.e. owl:someValuesFrom)
does not clearly communicate all of the semantics we may want for car parts.
For example, a strict reading of the definition of the Crankcase class above is
that a crankcase is part of at least one engine. In point of fact, a crankcase
cannot be part of more than one engine. We may be tempted to add a cardinality
restriction (e.g. maxCardinality 1) on partOf to the definition of crankcase,
but this would be a mistake; since partOf is transitive, a crankcase is also
part of the car the engine is part of. Note also that OWL-DL does not allow
transitive properties to have any cardinality restrictions. In general it is
best to avoid placing restrictions (including range restrictions) on transitive
properties at all. (034)
It would make more sense to add a restriction on the partOf_directly
property in the definition of these classes, when it is appropriate. A single
crankcase cannot be a direct part of more than one engine, an engine cannot be
a direct part of more than one car, etc., so in these cases a maxCardinality
restriction would make the semantics more clear. " (035)
So my question is, would agree that such discussions are useful for
clarifying issues in a general sense and with a particular represenation in
particular? Aren't we all invested in a general effort to "think clearly'? (036)
Gary Berg-Cross (037)
EM&I (038)
Herndon VA (039)
703-742-0595
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