What is the purpose of this line of discussion? I for one have absolutely no
idea what "instance of" means, if it is something which is sharply distinct
from "member of" between an entity and a set of entities, and therefore have no
idea what sense of "individual" is being discussed here. But my larger point
is, what point is served by setting out to achieve any kind of consensus on
this matter? (01)
Suppose that such a consensus were to be achieved, so that we had a wide
agreement on a notion of individual and of what it means to be an instance of a
non-individual; still, the question reamins of how this is to be formalized in
a logical language. (02)
Logics come with a built-in notion of 'logical individual', which means, things
in the universe of discourse, ie things that the language quantifies over, or
assumes to exist. It would seem natural then to assume that when formalizing
this consensus, the way to proceed would be to design the logic so that the
universe of discourse comprises these individuals, and therefore presumably
excludes the non-individuals. In a classical FO language, these non-individuals
would be the properties and relations which apply to or hold between the
individuals, and then presumably "instance of" would be mirrored by logical
predication, so one would write (P a) to mean that a is an "instance" of P.
However, this elegant picture means that "instance of" must be at least very
similar to set membership, since the only extant semantics for FOL treats
predication as meaning set membership. This does not actually require these two
notions to be identical, but it does impose a very tight constraint on what one
might call logical similarity between them. To be precise, "instance of" will
be *logically indistinguishable* from set membership: any way in which they are
dissimilar will be invisible in the logic itself; it will not be possible to
state axioms in the logic which capture this difference, whatever it may happen
to be. As far as formal ontologies are concerned, therefore, these differences
between instance and membership are irrelevant, and can (indeed, must) be
ignored. (03)
So perhaps we cannot simply identify individual with logical individual, but
must allow both individuals and non-individuals into the logical universe of
discourse, quantify over both of them, and have a sorting property IsIndividual
which allows us to assert Individual-hood of an entity:
(IsIndividual x)
Now we can, at least in principle, set out to write a formal ontology of
Individual-hood. Presumably, the relation instanceOf is also now in our
language, so we can write
(forall ((x IsIndividual) y)(not (instanceOf y x)))
which captures the suggested rule about individuals and instances, so is
plausibly an axiom of our nascent theory. (Any others?) (04)
But now we have partitioned our universe into two disjoint subsets. Why? What
useful expressive power have we achieved by having this distinction in our
ontology? Is it likely that there will be broad classes of things true of
things that satisfy IsIndividual which are not true of those that do not? Or
vice versa? If so, what kind of facts would these be? If not, what is the
purpose of making this distinction at all? What does it buy us? I submit that
until a clear answer is given to this question, we should not waste any further
time arguing over angels on pinheads. (05)
Pat (06)
On Dec 17, 2012, at 9:04 AM, doug foxvog wrote: (07)
> On Thu, December 13, 2012 11:55, Richard Dapoigny wrote:
>> Hi all,
>> I see that the debate about identification of individuals is far from
>> being consensual.
>> However, let us first (try to) agree of some fixed points as we say in
>> mathematics.
>> A usual definition is to see individuals as entities having no
>> instance(s). Is there some agreement about this first definition?
>
> This definition should be a little stronger (imho) -- to things that
> conceptually can have no instances in any possible world. This is a
> feature of the thing being modeled, not of the ontology, context, or
> knowledge base.
>
> "Unicorn" should not be an individual, since there can be instances in a
> fantasy world. Even if the intersection of two classes is empty (e.g.,
> "square circle"), that intersection should not be an individual even
> though it has no instances.
>
> I note that according to this definition, relations (if they are
> considered to be entities) are individuals, the application of a relation
> to a list of arguments, not fitting the definition of "instance" in the
> definition of "individual". If a member of a set is not considered to be
> an "instance" of the set, then sets are individuals. The same argument
> applies to "groups" of things -- whose membership can change, unlike sets.
>
>> This should help to better characterize the link between ontologies and
>> individuals.
>
> I note that OWL-DL distinguishes "classes" and "instances", as being
> disjoint. As such, classes of things (types of wine, animal species,
> models of car, ...) are often instances in OWL ontologies. Of course,
> such things can, themselves, have instances -- even though the
> impoverished language in which they are represented can not express the
> relationship between them and their instances as such.
>
> Some OWL-DL users use the term "individual" to refer to OWL "instances",
> even though those instances (in the real world) have instances of their
> own. These instances can not have their own instances expressed as such
> in OWL-DL (although they could be expressed in OWL-FULL).
>
>> All the best,
>> Richard
>
>
>> Le 13/12/2012 16:14, Amanda Vizedom a écrit :
>>>
>>> Hans, et al,
>>>
>>> Info Systems might not generally make that distinction, but
>>> Ontologies, and deployed ontology-based systems can, should, and often
>>> do.
>
>>> The unique name of an individual within an ontology is generally
>>> artificial, in order to guarantee uniqueness. Namespaces,
>>> Microtheories, and other mechanisms supporting ontology modularity
>>> serve to extend that uniqueness beyond the bounds of the original
>>> ontology or module. This is quite separate from any identifier used
>>> for the individual in any other system. Best practice IME is to map to
>>> identifier systems explicitly, using specific mapping predicates (for
>>> example, "socialSecurityNumber," "legalName," "vehicleIdentityNumber,"
>>> "serialNumber," "XYZemployeeID"); those predicates can and should
>>> themselves be defined with explicit reference to the context in which
>>> they apply or authority which issues and uses them. Note, also, that
>>> this approach is essentially neutral to metaphysical questions about
>>> the individual/class distinction, as identifiers can be, and often
>>> are, treated as contextual for any thing in the ontology, and mapping
>>> identifiers for classes is often done in precisely the same way, using
>>> specific mapping predicates whose context/authority is made explicit
>>> (for example, "modelNumber," "cHEBIName," etc.).
>
>>> This approach also eases things in deployed systems that are used to
>>> track (and perhaps eventually unify/identify) initially unidentified
>>> things using partial information.
>
>>> Best,
>>> Amanda
>>>
>>> On Thu, Dec 13, 2012 at 9:42 AM, Hans Polzer <hpolzer@xxxxxxxxxxx
>>> <mailto:hpolzer@xxxxxxxxxxx>> wrote:
>>>
>>>
>>> MW: Identity is different from identifier...
>>>
>>> HP: Correct! But information systems generally don't make that
>>> distinction because the only way they have of distinguishing among
>>> individuals is through identifiers -- which have context, usually
>>> implicit and overlooked. And one purpose of the "entity primacy"
>>> principle is to make developers explicitly aware of that
>>> distinction so that they don't mistake the identifiers they are
>>> using for individuals for the identity of those individuals (which
>>> is their own and inherent in their existence in some reality). The
>>> best we can do is to get socio-political agreement on some
>>> "near-innate" identifier for individuals, such as VINS for motor
>>> vehicles intended for use on public roads and MAC addresses for
>>> Ethernet devices. Such identifiers are useful for information
>>> sharing interoperability among diverse contexts about the same
>>> individuals. But we don't really have such an identifier for
>>> people (yet). Maybe some "superDNS" identifier certificate issued
>>> independently of national/local jurisdiction before birth to all
>>> people (like VINs) will be brought about thanks to the Internet,
>>> but I'm not holding my breath. Or maybe some biometric will be
>>> found that can serve as this "near-innate" identifier on the
>>> network. And we need to be vigilant and remember that even these
>>> identifiers are not the same as identity and that the individuals
>>> may have other identifiers in other contexts.
>>>
>>>
>>>
>>>
>>>
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>>
>>
>> --
>> And the wounded skies above say
>> it's much too much too late.
>> Well, maybe we should all be praying for time.
>>
>>
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