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RE: Re: semantics in schema (xsd)


xsd ontology
As has been pointed out:

1.  The problem is not with the ontology technology.  The problem 
is with rules applied to membership that are then assumed 
to have a meaningful relationship to real world entities, 
particularly in the the co-occurrence constraints (business rules).

2.  That the scope of application and the abstract domain 
are not necessarily the same.

3.  That the best approach to implementing these can be 
to create an extensible enumeration of the relationship 
types given that the domain of application may vary 
significantly by locale, that is, the ontology itself 
may have to be very weak to have a global scope.

Regardless of the purity of the abstractions of the 
ontological instance or its metalanguage, the social 
dimensions of the application domain are a powerful 
selector of the technology applied, where the 
rules and relationships are declared and what they 
are locale by locale.

In the example provided, the problem of a single viewpoint 
is clear:  at the Constitutional level, at the Federal level, 
at the state level, at the agency level, at the 
individual level, the ontological distinctions 
and the co-occurrence values are distinctly different.

len


From: Pete Kirkham [mailto:pete.kirkham@b...]

(a little late as I've been away for a long weekend)

Irene Polikoff:
> Well, this seem to go back to the question of whether "husband" should
> be treated as a class - a subclass of males or as a relationship (object
> property).

In the ontology, the class describes a set of things with common properties,
this 
should not be confused with a type in an information model/schema or a class
in an 
OO implementation that encapsulates the data that represents the information
that 
is a viewpoint on the abstract concept that is described by the ontological 
classification.

So the ontology may have husband as a class- as there is a 'meaningful' set
of 
human individuals that share the properties maleness and marriage, and an 
information model for on application of that ontology may only have the
capability 
of representing husbands with female spouses. All information models of real
world 
situations appear doomed to incompleteness.

David Megginson:
> I'd say forget about classes and make your objects big bags of properties 
> (attributes and relationships).  The main advantages of classes for 
> object-oriented programming -- code reuse and type-safe polymorphism -- 
> don't even apply to simple information representation, so why pay the
costs 
> of a class structure if you don't receive any benefits?

The benefit of classifying concepts gives a shorthand to help us reason
about 
things- it's easier to agree what a husband is, then talk about what
information 
the application needs to represent about or process when dealing with
husbands than 
it is to always talk about 'individuals who are in a legally married state
who are 
also male and human'. 

>   There exists an entity A.
>   A is human.
>   A is male.
To me, at the ontological level, these are classes, irrespective of whether
or how 
you choose to implement the data level in static typed OO software.

Given all statements may have a temporal limit, there's no problem with one
web 
page from 1997 saying 'Fred is a husband' and another from 1993 saying 'Fred
is not 
a husband'; OWL specifically notes that data in web documents may change and
be 
inconsistent. If not, then nothing would be able to be classified, as
nothing real 
is permanent. In OWL, even if you define only the relations, I can define a
class 
based solely on the presence of those relations, and declare that your
statements 
indicate a classification. AFAICT this is the main interoperation mechanism
that 
OWL uses- saying that from your information model {x: x is a Human & x is a
Male &  
x is married to y} is equivalent to my {x: x marital status = husband }
class, if 
my information model only represents marital status as an enumeration. Such 
mappings apply only for the information mapped, so tomorrow an individual
may be in 
a different classification.

It's always possible to construct classes from relationships in the
ontology, and 
this seems to be done best by what is meaningful in the domain.

In the information model, the types will be based on what is useful to the 
applications that are using the information. It may be useful to limit
husbands to 
current heterosexual relationships for one application, for another (e.g. a
pension 
scheme), the instances considered as members of the husband type may include

deceased partners.

The software constructs that encapsulate the data may end up being very
different 
to the ontological classifications and the information model types, simply
because 
the software has to be written a certain way to work. Hence, in a static OO 
language, you end up with David's implementation, irrespective of the
concepts 
embodied. But capturing the classifications that make up the ontology
shouldn't be 
constrained by the limits of one programming paradigm that may be used to
implement 
one application in that domain.


Pete

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