Jeffrey Schieffel wrote: (01)
>> An ontology is intended to define the terms of a domain, and the
>> relationships ... It enables semantic interchange. (02)
>> If two agents, each using an ontology, cannot exchange terms that can
>> be fitted into the respective ontology each is using, then they must
>> be using
>> different, non-overlapping ontologies. These two ontologies would be
>> orthogonal. No term or relation in one ontology would have meaning in
>> the other. The ontologies would be mutually exclusive. (03)
I think we are talking past one another. My email was directed at the
inaccuracies in this characterization of "semantic interchange", as
distinct from whether there was a usable definition of "orthogonality"
somewhere in there. (04)
My position is that two agents don't need to have non-overlapping
ontologies to be unable to communicate effectively. Their ontologies
can have a 90% overlap, but if there is one critical idea that one has
and the other does not understand, they can't do business. (05)
The example:
>> If you think Cairo is a city in Egypt, and I think Cairo is a city in
>> Illinois,
>> then we know we are talking about different places; but if the shared
>> ontology
>> only tells us that Cairo is a city, we may think we are talking about
>> the same place. (06)
Jeffrey wrote:
> Yes, but I am not talking about sharing. I'm defining orthogonality. (07)
Surprise! I presumed that a discussion of communication between agents
and "semantic interchange" was about "sharing". My error. (08)
> As for the Cairo example, two points. First, if both ontologies have
> _city_ in them, then there is at least one shared concept, hence they
> are not orthogonal. (09)
Indeed. My point was that it the existence of the common concept does
not guarantee that any related term can be exchanged. If there is one
term that cannot be fitted into one agent's ontology, in this case the
concept "Egypt", that is sufficient to cause communication failure. (010)
In Pat's terminology, if there is ONE term in ontology O that does not
have a "definition" that can be proved in ontology P, that is, if *one*
term in ontology O 'is orthogonal to' P, then the communication between
the agent using O and the agent using P is "impaired". And if that term
is critical to the reason for the communication (i.e., the 'joint
business process'), then the communication between them is *critically
impaired* -- they cannot safely or effectively execute the joint process. (011)
(I should mention that this is precisely the focus of work in my group
at NIST, which is why it is important to me to clarify this.) (012)
> For that matter, the name _Cairo_ needs to be
> disambiguated only when written. The Egypt and Illinois cities are
> pronounced differently, so there is no conflict in the instances. (013)
This is irrelevant. In point of fact, the term needs to be
disambiguated when written and when the characters are encoded in
automated exchanges, which is a substantial majority of business cases.
When the communication is verbal, we are talking about the mental
'ontologies' of the human agents, which is rather beyond our scope. And
in that case, it is probably true that both names spelled "Cairo" in
English have different pronunciations by different agents. In
Louisville and Natchez, they pronounce it Keruh, and in Egypt it is al
Qairah. So even human agents would have to sort out differences in
pronunciation which are regional from differences in pronunciation
intended to differentiate terms. (I am reminded of the New Yorker who
thought "Milla's Dock" was a Boston beer, while "Milla's Dawk" was made
in Milwaukee, where of course, it was pronounced "Miller's Dark". :-)) (014)
> The Cairo example brings up an additional point that was in Alexander
> Garcia Castro's original question. It is: is there a measure for
> orthogonality? My take is that if orthogonality is a matter of degree (I
> stated it isn't), then the underlying question is one of semantic
> distance. (015)
Well, the definition of orthogonality between ontologies as stated by
Pat (which mirrored my less careful phrasing) is certainly yes/no. But
it makes use of the concept 'orthogonality' of a term to an ontology.
The number of orthogonal terms between two ontologies might be a measure
of "semantic distance". (016)
> This, then, raises the further question of the two kinds of tags in an
> ontology, the tags for concepts, and the named instances of the concepts
> in the ontology. I suspect the semantic distance is measured by the
> instantiated elements. (017)
Ultimately, the communication between two agents will succeed if they
both associate the 'things' that arise in their joint activity with the
mutually agreed-upon behavioral concepts. The universe of discourse for
the joint activity is just the things at hand and the actions taken.
The actual meaning of the concept in a larger world is not important. (018)
And in a larger sense, coextension of concepts may be just as useful an
indication of "semantic equivalence" as "provable definition". But
provable definition guarantees coextension, and the only other mechanism
of proving coextension is total enumeration. (019)
A priori, the two communicating agents only know some of the relevant
instances -- the others are less predictable. "Cairo" can be an element
of the ontology that corresponds to a specific 'thing' in every/any
related UoD, or it can be a 'thing' that arises in the active situation,
where both agents classify it as 'city' and 'destination', because of
ontological alignment. (020)
But Agent X and Agent Y both have internal ontologies that are *larger*
than the *shared ontology* for the joint activity. When all Agent X
gets is "Cairo", because the concept "Country of destination" was not
shared, his internal ontology may implicitly supply the value "USA" (it
is amazing how insular Americans still are). And agent Y may understand
"country" as a significant element of a destination, but be able to
deduce it from the city identifiers in his normal universe of discourse,
unaware that the designation "Cairo" isn't unique in the actual universe
of discourse for the joint activity. (This is yet another version of
the problem Pat Hayes refers to as the "Horatio Principle" -- there are
more things in heaven and earth, Horation, than are dreamt of in your
philosophy.") And that makes extensional measures of semantic distance
quite tricky. (021)
-Ed (022)
--
Edward J. Barkmeyer Email: edbark@xxxxxxxx
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694 (023)
"The opinions expressed above do not reflect consensus of NIST,
and have not been reviewed by any Government authority." (024)
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