Heres another example. Cyc lists all the chemical elements, and cross-
links to other such lists in other ontologies using owl:sameAs. But
the Cyc ontology says that an element is the set (class) of all pieces
of the pure element, so that for example sodium in Cyc has a member
which is the lump of pure metallic sodium I keep safely under glycerin
in a glass bottle on my shelf. This is a clever ontological device
which makes a bunch of inferences very slick in Cyc, but I bet its not
the same *idea* of sodium that most ontologies would agree with. So
that sameAs ought to be (and it is understood as meaning) 'same
chemical element', but it does not allow mutual substitutivity, even
if you were to translate those other ontologies into CycL, which
nobody is ever likely to do.
Pat
On Jul 21, 2009, at 7:58 PM, Pat Hayes wrote:
On Jul 21, 2009, at 7:26 PM, Alan Ruttenberg wrote:
On Tue, Jul 21, 2009 at 1:23 PM, Toby Inkster<[email protected]> wrote:
On Tue, 2009-07-21 at 19:52 +0300, Bernhard Schandl wrote:
I would say: Never assert sameAs. It's just too big a hammer.
Instead use a wider palette of relationships to connect entities
to other ones.
which ones would you recommend?
skos:exactMatch = asserts that the two resources represent the same
concept
Say, refer to the same thing.
, but does not assert that all triples containing the first
resource are necessarily true when the second resource is
substituted
in.
I'm having trouble parsing this one. I don't know what concepts are,
but they are an odd sort of thing if they can be the same, but can't
be substituted.
This is exactly what is needed in many cases. Philosophical
terminology is that they have the same referent but not the same
sense, and lack of substitutability reflects the unfortunate but
inevitable fact that the Web as a whole is not referentially
transparent (yet). More mundane example, the same person might need
to be referred to in one way in one context and differently in
another, just because the two social contexts require different
forms of address. (That example from Lynn Stein.)
In any case, this isn't much better when the issue I point out is
that
there is a specific relation between e.g. the intervention and the
drug - that relation is no where near equivalence in any form.
True, but in cases like this, it is simply a basic conceptual
mistake to be using any kind of loose-sameAs property. rdf:seeAlso
would be more like what is needed for linking a drug to an
intervention. I agree with you about having a selection of better-
thought-out relations rather than just using sameAs as a kind of all-
purpose knee-jerk connecting link. Maybe this "Linked Data" slogan
has a rather dumbing-down effect, as it suggests that 'link' is a
simple uniform notion that works in all cases.
skos:closeMatch = same as exact match, but slightly woolier.
Seems harmless, assuming one doesn't mind whatever one is dealing
with
typed a concept.
Ditto the broader and narrower relations, which although not to my
taste (i don't how to tell when they hold) are certainly better than
using sameAs.
owl:equivalentProperty = if {X equivalentProperty Y} and {A X B}
then
{A Y B}. In other words, the properties can be used completely
interchangeably. But perhaps there are other important differences
between X and Y, such as their rdfs:label or rdfs:isDefinedBy.
Still near equivalence.
owl:equivalentClass = if {X equivalentClass Y} then all Xs are Ys
and
vice versa. Same dealy with owl:equivalentProperty really.
Ditto.
ovterms:similarTo = a general, all-purpose wimps' predicate. I use
this
extensively.
Under the principal "first do no harm", this seems to work,
although I
note that the intervention (something that happens) isn't similar to
the drug used in it (something that is consumed when the intervention
happens).
seeAlso seems pretty harmless and noncommittal.
But better is probably to look more closely at what the entities are
and then choose a relationship that better expresses how they relate.
In the case of the intervention, one plausible interpretation is that
the "intervention" names a class of processes, and that there is a
subclass of such processes in which the drug participates. (the other
subclass are those in which a placebo is the participant) This can be
modeled in OWL.
(My real advice for clinical trial resource is to collaborate with
the
OBI project and use terminology that is being developed for exactly
that purpose)
In my line of work I start with the OBO Relation ontology,
http://www.obofoundry.org/ro/ which provides a basic set of well
documented relations, such as the has_participant relationship.
OWL also provides some relations of beyond equivalences - subclass
relations are an option, when appropriate, as well as making
statements that classes overlap - by expressing that the intersection
of the two is not empty.
That ontology is undergoing some reform, as it should in time. Some
of
the new candidate relations are documented in links from that page.
In
addition it is proposed that that there be class level and instance
level versions of the relations - the class level relations might
better a modeling style that would rather avoid using OWL
restrictions, and fits well with OWL 2 which allows a name(URI) to be
used as both a class and an instance.
Finally, for those cases where there are more than one URI and they
*really* mean the same thing - why not try to get the parties who
minted them to collaborate and retire one of the URIs. If they really
mean the same thing there should be no harm in either party using the
other's URI.
Its not that simple, unfortunately. I'm going to make this issue the
center of my invited talk at ISWC later this year :-)
Pat
-Alan
--
Toby A Inkster
<mailto:[email protected]>
<http://tobyinkster.co.uk>
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