A response to Ali’s note (Wed March 3, 11 PM EST):
Thanks for presenting the contrary position. Specific answers
are in-line, but here one general comment.
The process of creating mappings and translations between
different ontologies as I understand your approach is not disjoint with the use
of an FO. I completely agree with your point that an expressiveness at least
equal to FOL is needed for accurate mapping. And if specific mappings are
created between two particular ontologies, those mappings may be as accurate
and more efficient than generating mappings by means of a common FO. So specific
pre-existing mappings can be used if they exist, and mapping via the FO can be
used if specific mappings don’t exist. If you have some direct
mappings, the FO can be used as a backup where direct mappings (or transitive
equivalence relations) don’t exist. If some set of ontologies is mapped
to an FO in such a way that one can describe every element in every ontology
using only the elements of the FO, then whatever you choose to call the FO might
function as I would hope the FO to function. But mapping every ontology to the
FO seems to me to take a lot less effort than generating multiple mappings between
the ontologies of that set. And the transitive mappings available using individual
ontologies mapped to a common ontology would be accurate only for an
equivalence relation, which seems unlikely to hold for more than 70% of the
types in any two ontologies, and fewer when there is an intermediate ontology.
But even that only deals with the types (classes). The more important mappings
are for the semantic relations, and these are very difficult to map, being as
their meanings (if domain and range are used) depend on the hierarchy and on logical
inferences, and if the hierarchies are not exactly the same, it seems that it
will be very hard to translate the semantic relations. It is still hard to
translate semantic relations using an FO, but if all semantic relations are
expressible using the FO terms, it at least becomes possible.
I emphasize that the goals of mapping between domain ontologies and
using the FO are not incompatible, I just believe that there are things you can
do with an FO that are not possible or not practical by trying to map among
multiple ontologies without generating an FO. You seem to think that specific
mappings will be adequate. But I am especially concerned with information on
the internet for which the ontology has not been mapped to yours. The FO
covers that case automatically, I can’t see how specific mappings can.
More details on specifics below.
Patrick Cassidy
MICRA, Inc.
908-561-3416
cell: 908-565-4053
cassidy@xxxxxxxxx
From:
ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ali Hashemi
Sent: Wednesday, March 03, 2010 10:11 PM
To: [ontolog-forum]
Subject: Re: [ontolog-forum] Foundation ontology, CYC, and Mapping
Dear Pat C,
I do not doubt that everyone on this list can think of some additional
*potential* problems with this process. But the first question to be
answered is: is there a better process to support very broad semantic
interoperability with the same accuracy?
There are number of other ways this interoperability may be achieved, without
recourse to a single FO.
First, if theories in a repository are suitably modular, each module on it's
own (set of axioms) is an ontology. Additionally, every combination of modules
(that is consistent and makes sense) is also a unique ontology.
[[PC]] The cases I have seen where pluggable modules exist and
don’t depend on some ontology of more fundamental concepts to specify the
meanings in the modules cover a tiny, **tiny** fraction of what one would need
in an ontology useful for practical purposes. Perhaps I have missed some
important developments. Can you provide me with examples of applications using
ontologies developed from pluggable modules?
Moreover, one need not agree on a unique set of primitives. There might be 7-8
different sets with mappings between them, but no real "join" or
generalization of the primitives - i.e. 7-8 different FO's that all efforts
have been unable to merge.
I.e. instead of a single hub-spoke, you have 7-8 hubs and ensuing spokes, with
the hubs connected to one another.
[[PC]] How would the hubs be connected to each other? If the mappings
are not 1 to 1, what kinds of relations would have to be defined? Would you
introduce new more basic elements to create the translations among the 7-8 hubs?
Would accurate translations be possible? (If they are 1 to 1, the ontologies are
essentially identical, a case I have never seen).
Here’s a dichotomy: (1) two candidates for an FO are
logically contradictory. Attempted mappings without stringent effort to
isolate and avoid the inconsistency may cause disastrous errors in translation
among them.
(2) the two candidates are not logically contradictory. IN that
case they should be able to be merged. It may take considerable effort, but if
the original ontology developers are around to resolve ambiguities as the
mapping process takes place, it should be possible. Without the originators
available, in general the ambiguities will leave considerable uncertainty and
make mapping highly error-prone. Except for CYC, the ontologies I have seen in
general have many ambiguous types and even more ambiguous semantic relations.
And the best way to avoid ambiguities is to have the domain ontologies
specified using a common set of primitives, which have been thoroughly reviewed
and tested and documented to be sure that their meanings are clear.
Anyway, the basic idea re mapping is still the same. That merge engine which
you allude to can manifest in a number of ways. If the relationships / mappings
between ontologies is already recorded in the metadata (i.e. T1 faithfully
interprets T2 given mapping module T1-2) a simple reading of the metadata should
be able to specify a mapping. Note, all this is quite independent on requiring
anything to go through an FO.
[[PC]] Sure, if you have enough metadata - but the point I was
making was that creating the metadata to do such mappings is going to be a lot
faster if you develop an FO with primitives. If you have a merge engine that
can actually properly relate ontology elements in independent ontologies, it
will in effect be using an FO with primitives, except for those minority of
cases where there are accurate 1-1 maps for all ontologies in the mix.
If mappings don't exist, we're still in luck. There's a semantic mapping tool
(prototype in my MASc thesis, updated version coming out soon) which does
exactly what you wanted. It finds where two ontologies agree, where they differ
and on what terms. It can do it wholly automatically, but it is not very
efficient (it would test all possible relations between terms, whereas a human
could suggest which term-term relations to explore). It does this using any
referent onotlogy, it need not be an FO, but it could very well be an FO...
[[PC]] I will certainly be interested in seeing the concrete
results of any mapping tool that appears to perform well enough to sustain some
level of accuracy over an inference chain of say 6 to 12 in length. The paper
you referenced by Euzenat surveying ontology mapping indicates the problem that
makes me despair. An F value of less than 80% may be interesting and
potentially useful for generating search results to present to humans, but is
utterly hopeless for logical inferencing. And what I am aware of seems to be
the easy part. Since all of the meaning in an ontology comes from the logical
inferences generated by the semantic relations, the most important matching
would be for the semantic relations. Can you point me to a specific paper that
shows promising results for that task? Is your thesis accessible on-line?
The above comments distinguish two different issues that can
be discussed
separately: (Issue1) do we actually *want* every meaning in the FO itself to
change when a new element is added, or do we have criteria of performance
for the FO that guard against unintended changes? (I would use a test
application suite to detect and avoid unintended changes) And
(Issue2) given that the meanings of domain types will differ when different
specialized types are created in domain ontologies, how will this affect the
performance of the FO as a support for interoperability? (There will be
no
contradictions, but less certainly as to whether inferences about a given
subtype in one domain do or do not apply to the parent type or a different
subtype in another domain).
This is a question of how people want to use their given ontology. Often, the
terms defined in an FO are wholly unnecessary for the application domain.
Say I have a manufacturing plant, and I have some machines, employees and a
process. I might not really care about the philosophical implications of
whether number is a subtype of abstract entity. This suggests to me that it
might be limiting to commit to a particular FO. But whatever, let's work out an
example within the context of a single FO.
I care about processes, actions and the agents that perform them. If I want to
to communicate with another plant, we still don't really need to agree on an FO
in its entirety. All we need to figure out is what our systems are committing
ourselves to. At most (if at all), we would only plug into a sub-component of
the FO.
Now, if any such FO is suitably modular, then the addition of a novel element
need not change the meaning across the board.
In fact, I suggest it is misleading to refer to the FO as a single ontology. It
is really a collection of ontologies, and depending on which modules you decide
to include, you have a different ontology each time. So were I to plug into the
FO, i would care about the modules pertaining to Processes (which might take me
to activities, time, duration etc.), and another module about agents taking me
to people, robots, etc.
[[PC]] There may well be parts of the FO that can be segregated
out as modules (I have separable modules in the COSMO, such as one for mapping
the ontology to databases, with database-specific types and relations), but
there will have to be an indispensable framework that integrates the modules, and
my experience with COSMO suggests that that would be well over half the
ontology. I also anticipate that users will want a tool that takes the FO and
some domain ontology specified using the FO, and extracts from the FO only
those elements required to create the domain ontology. This would be useful to
minimize the resulting ontology for computational efficiency, and would not
require that the FO be modularized (though that wouldn’t hurt). In
general it will be unpredictable what modules are needed for the next ontology
you encounter on the internet. See the next comment.
I need not commit to the whole FO, just parts of it. A change in a module that
i'm not plugged into (or more general than it), would not change the ontology.
[[PC]] Fine for any two ontologies that are directly hand-mapped.
What do you do for information posted in the internet, assuming that you have
the ontology the posting group uses? How accurate would an automatic mapping
be under those circumstances? The merging process for different ontologies can
be automatic and accurate if the elements of domain ontologies are logically specified
only from elements from a common FO. But I cannot visualize how any automatic
mapping can achieve any level of accuracy without the use of a common standard
of meaning that can express all the elements in the ontologies to be mapped. I
would be fascinated if you could show an example of a mapping between
independently developed practical-sized ontologies (non-toy ontologies, used in
some application) that can give a mapping accuracy of at least 99% for both
classes and relations. Or at least outline a procedure that you think can do
that.
End of comments.
PatC
Even if it were, the distinction between conservative and nonconservative
extension plays a role too. In Pat Hayes' example, if the previous definition
of human was silent on these novel properties, those new properties would be a
conservative extension, and the addition of M's axioms would essentially be
orthogonal to my original reasoning process.
Now in terms of intended meaning, it makes a huge difference. In terms
of reasoning, it can be neatly delineated. However, if the extension were to be
nonconservative, we still have a change in intended meaning and the change in
logical meaning is complicated as well (though still manageable if modules are
used).
Cheers,
Ali
--
(•`'·.¸(`'·.¸(•)¸.·'´)¸.·'´•) .,.,
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