Woops
sorry, that got sent off before I was finished:
And here is a small
document that validates against that schema:
<?xml version="1.0"
encoding="UTF-8"?>
<assembly xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="C:\Documents and
Settings\murraypx\Desktop\example.xsd" name="Bicycle">
<part name="Front
Wheel"/>
<part
name="Back Wheel"/>
</assembly>
-Paul Murray.
Hi,
By way of example, here is a tiny xml schema for parts
and assemblies:
<?xml
version="1.0" encoding="UTF-8"?>
<!--W3C Schema generated by XML Spy
v4.4 U (http://www.xmlspy.com)-->
<xs:attribute name="name" type="xs:string"/>
<xs:attributeGroup
name="core">
<xs:attribute
ref="name"/>
</xs:attributeGroup>
<xs:element
name="part">
<xs:complexType
mixed="true">
<xs:attributeGroup
ref="core"/>
</xs:complexType>
</xs:element>
<xs:element name="assembly">
<xs:complexType mixed="true">
<xs:choice minOccurs="0"
maxOccurs="unbounded">
<xs:element ref="part" minOccurs="0"
maxOccurs="unbounded"/>
<xs:element ref="assembly" minOccurs="0"
maxOccurs="unbounded"/>
</xs:choice>
<xs:attributeGroup
ref="core"/>
</xs:complexType>
</xs:element>
</xs:schema>
*Note: changed to
ontolog-forum@xxxxxxxxxxxxxxxx in above cc line (was incorrect).
I am unclear as to how the XML Schema constraint addresses a real world
object.
Also, note that the structures on the semantics side are based on set
theory. So these are structured mathematical objects.
"Murray, Paul" wrote:
"A
constraint in an XML Schema is a constraint on the structure or form of a
document, not on the meaning of a real world object as in an
ontology."Not necessarily true, a
constraint in an XML Schema (say the parent/child element/attribute
relationships) can also translate to a constraint on a real world object
as in the "part-of" relationship. But I guess this is a
nit. I think an important statement here
is:*However, we all know that
structure is the mother of meaning too, that in fact no semantics is
possible without it, and that the formal objects on the "semantics" side
to which the syntax/structures map (in model-theoretic semantics via an
interpretation function) and which we take to "stand in" for the
real/possible world entities whose semantics we want to capture, are
themselves structured (probably because we want those objects to have
certain formal properties, ordering relationships, etc.) -Paul Murray.
We've recently been discussing a variant of
this question internally (in MITRE) across two communities, the database
and the ontology folks. I.e., data modeling vs. ontology engineering. I
think our point of departure was the SIGMOD paper from last year:
Data Modelling versus Ontology Engineering. P. Spyns, R. Meersman, M.
Jarrar, Special Section on Semantic Web and Data Management, V. 32:4,
December, 2002. http://www.acm.org/sigmod/record/issues/0212/SPECIAL/2.Meersman.pdf.
Note the above requires a login account.
I think the short answer is that database schemas and XML Schema are
a way of structuring data/document collections for some generally local
purpose, e.g., to satisfy an application (or set of applications) or, in
the case of XML Schema, for some generally local exchange of
documents/messages. So, in general, schemas are focused on
structure rather than the meaning of constructs that define that
structure. And ontologies address a more "global" view, in terms of real
world semantics.
*However, we all know that structure is the mother of meaning too,
that in fact no semantics is possible without it, and that the formal
objects on the "semantics" side to which the syntax/structures map (in
model-theoretic semantics via an interpretation function) and which we
take to "stand in" for the real/possible world entities whose semantics
we want to capture, are themselves structured (probably because we want
those objects to have certain formal properties, ordering relationships,
etc.)
That said, maybe the shortest answer is: A constraint in an XML
Schema is a constraint on the structure or form of a document, not on
the meaning of a real world object as in an ontology.
Leo
"Uschold, Michael F" wrote:
It is not usual for someone to show me an XML
shema and say, "Hey, what do you think of my ontology?", or: "Gee, we
are using an ontology now, but everyone's using XML, so maybe we
should use an XML Schema instead?". Indeed, some people
have the impresson that XML Schema and ontologies** are similar
animals and one can use one or the other for a given problem.
Where does this impression come from?
For SOME problems, ontologies and XML Schema seem for all practical
purposes, to be alternatives. One can create an ontology and a data
set conforming to that ontology, or one could create an XML schema and
pass data conforming to that schema. There would be a clear
mapping between classes and attributes in the ontology and elements
and attributes in the XML schema.
However, I believe that for MOST problems ontologies and XML schema
are not appropriately seen as alternatives, indeed they are quite
different animals for quite different purposes, and can be used to
good effect together complementing each other.
Can anyone resolve this paradox? One great way to answer the
question is like this:
If properties p1, p2, ... pn hold for a given situation, then
for most practical purposes, XML schema and ontologies can be viewed
as alternatives. This is because <now explain how properties
p1-pn make this so, and why when those properties do not hold, the
situation changes and how.>.
What are the properties? I would guess that one has to do with the
intended purpose of the ontology/schema. Related to this would be
inference requirements.
Thanks,
Mike Uschold
** For now, lets say by ontology I mean a simple language like OKBC
or even RDFS that one can use Protégé for. --
_____________________________________________
Dr. Leo
Obrst The MITRE Corporation
mailto:lobrst@xxxxxxxxx Intelligent
Information Management/Exploitation
Voice: 703-883-6770 7515
Colshire Drive, M/S H305
Fax:
703-883-1379 McLean, VA 22102-7508,
USA --
_____________________________________________
Dr. Leo Obrst
The MITRE Corporation
mailto:lobrst@xxxxxxxxx Intelligent
Information Management/Exploitation
Voice: 703-883-6770 7515 Colshire
Drive, M/S H305
Fax: 703-883-1379
McLean, VA 22102-7508, USA
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