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Re: A proposed solution to the RDF syntactic/semantic mapping problem (long)

From: Jonathan Borden <jborden@mediaone.net>
Date: Mon, 11 Jun 2001 11:35:39 -0400
Message-ID: <002e01c0f28c$2bf65100$0a2e249b@nemc.org>
To: <Patrick.Stickler@nokia.com>, <www-rdf-interest@w3.org>
Patrick:

>
> === Claims ===
>
> Claim 1: A namespace and name pair does not constitute any kind of
> universal semantic identity, only a unique syntactic form which
> can be associated with some semantic identity.

Since I have no idea what a "universal semantic identity" is, nor do I know
if one exists (I strongly suspect that there does not exist 'universal'
agreement on any of these issues) this statement is probably true.

>
> Although names within namespaces do serve to differentiate content
> which is attributed meaning, and that meaning is typically (though
> not necessarily) suggested by the linguistic properties of that name,
> the syntactic form selected for any particular serialization is
> local to that serialization and many syntactic forms may map to the
> same common semantics.

Yet XML Schema, for example, uses QNames not URIs to denote types, so really
depending on the application, either a QName or a URI may be the primary
means of identifying some 'thing'.

> The syntactic form provides a mechanism
> by which we may define a mapping to that universal meaning, but it
> does not serve itself as the universal identifier of that meaning.

Again, not sure how a URI universally identifies a "meaning". It identifies
a resource but isn't it the point of an ontology/schema etc to define a
"meaning"?

>
> Likewise, a namespace does not officially identify any ontology or
> semantic space, even if it is often used to do so, but only is a
> syntactic mechanism by which name collisions are avoided in
> the syndication of arbitrary syntactic forms in a given serialization.
> There is no requirement whatsoever that a namespace provide any
> semantic identity.

"semantic identity" what is that? An XML Namespace name _is_ a URI
reference -- hence inherits all of the properties of a URI reference.

>
> Claim 2: A name within a given namespace does not equate to a URI
> reference of that name within any content dereferencable from the
> namespace URI reference.
>
> I.e. "namespace" + "name" != "namespace#name".

I suppose it depends on what you expect the "name" to reference.

I consider this a bug not a feature.

... Furthermore, as a
> given namespace may have serializations defined in various schema
> formalisms, each potentially having different MIME content types
> with potentially different fragment schemes, yet all defining
> the same namespace URI and name, there is then potentially a many to
> one mapping from namespace and name pair to URI reference into each
> of those schema instances.

This is a mess.

>
> Claim 3: We cannot use concatenation, suffixation, insertion or
> any other method of combining a name with a namespace URI reference
> to obtain a compound URI reference without violating the sanctity of
> either the URI scheme and/or some MIME content type fragment syntax
> space.

What sanctity? We need to define practical and interoperable ways of dealing
with QNames and URIs. The _goal_ is to create systems that work, not to
maintain URIs and RFC 2396 on a pedestal, even when that pedestal is sitting
right in the middle of the Santa Monica freeway -- or I-93.

>
> Likewise, it is not possible to reliably re-partition any merged namespace
> plus name URI reference back into its namespace and name components
> which is necessary for re-serialization of knowledge (see discussion
> and examples below regarding bi-directional serialization mapping).
>
> Claim 4: The current methodology employed by RDF to attempt to create
> a semantic resource identity by direct concatenation of namespace
> and name does not ensure the preservation of the uniqueness of namespace
> qualified names.

agreed.

>
> This example, along with the discussion in claim 2 about unclear
> re-partitioning of combined URI references, demonstrates the fact that
> the uniqueness of a namespace and name pair has three elements:
> (1) the unique namespace,
> (2) the unique name within that namespace,
> and
> (3) a distinct boundary between the two.

agreed.

>
> Step 2: Provide for explicit mapping between syntactic forms and
> semantic resources. I.e. for mapping rdf:ID values to rdf:about values.
>
> This is achieved by the following two methods:
>
> Mapping method 1: RDF

Why not "daml:equivalentTo" or "rdfs:isDefinedBy"?

Isn't that the role of an ontology?

>
> Mapping method 2: RDF Schema

[snip]

I agree that this mapping is needed. I would prefer to see such a mechanism
within RDFS/DAML.

[snip]
>
> === Regular expression constraints on syntactic literals ===

this seems an extension of RDF aboutEachPrefix... an interesting idea and I
can certainly see how it might be useful but given the problems that
aboutEachPrefix has had in gaining traction, it would be hard getting this
accepted.

In summary I completely agree that the QName <-> URI issue is one that needs
to be clarified.

-Jonathan
Received on Monday, 11 June 2001 11:52:47 GMT

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