Re: Linkbases, Topic Maps,and RDF Knowledge Bases -- help me understand, please

["Eve L. Maler" <eve.maler@east.sun.com>]

At 10:32 AM 4/6/01 -0600, uche.ogbuji@fourthought.com wrote:
> > Even though XLink and RDF are targeted at different purposes, it's still a
> > fair observation that XLink has a lot (not all) of the power of RDF.  For
> > info on a suggested way to map XLink to RDF, see the note "Harvesting RDF
> > Statements from XLinks":
> >
> >    http://www.w3.org/TR/xlink2rdf/
>
>I strongly disagree with this.  Just because basic RDF graphs can be
>"harvested" from XLink doesn't mean that XLink has a lot of the power of
>RDF.  RDF can be harvested from HTML as well, but that says nothing about
>the power of HTML relative to RDF.

I'm sorry you took offense.  Maybe I should have separated my first and 
second sentences into two paragraphs.  The Note I referred to doesn't 
directly talk about the conceptual/data model similarities to XLink and 
RDF, but surely it's obvious that they exist, and the Note shows the most 
obvious way: usage of roles and arc roles in constructing assertions.  (The 
role stuff in XLink was explicitly added to allow for clean mapping to RDF 
statement semantics, and this choice was supported by and coordinated with 
some RDF folks.)

I was not trying to say you could simply use XLink for metadata purposes or 
to cheapen RDF; rather I was pointing out that even though you can force 
them both into somewhat similar molds, they don't have the same purpose and 
so each has its place.  For example, XLink has "traversal" semantics that 
RDF doesn't, and RDF has (as I understand it) "bag" semantics that XLink 
doesn't.

>With enough contrivance, one can, of course, get everything RDF can do in
>XLink, for instance, one could use XPointers referring to XLink elements
>to simulate reification, and one could concoct a schema system, but this
>isn't a useful counter to RDF's facility.
>
>And then again there are aspects of RDF that are pretty much outside the
>capacity of XLink, such as the flexibility of RDF's XML serialization
>(which can be burden as much as boon, but is a fact).
>
>I actually don't think there's much overlap between RDF and XLink at all.

I have to disagree, but I'm not really trying to get into a boxing match 
over which is "better"; I think they both have their strengths and use 
cases, and the RDF-knowledgeable people with whom I've worked in doing 
XLink stuff have agreed.  My post was merely intended to inform people 
about a resource that describes some ways in which they are conceptually 
similar.

         Eve
--
Eve Maler                                             +1 781 442 3190
Sun Microsystems XML Technology Development  eve.maler @ east.sun.com