Article:		Building a Semantic Web Site
Subject:		An Approach to the Semantic Web
Date:		2001-05-10 01:54:51
From:		Eric van der Vlist
Response to: An Approach to the Semantic Web
I will try to give this sequel keeping a "fair and equal treatment to RDF and XTM"... As a preamble, I would say that the availability and quality of the meta information is more important than the serialization format (RDF, XTM or any other). I see RDF and XTM as belonging to different levels, though and believe they should be more complementary than competing. RDF is a very generic syntax to express facts as triples while XTM is an application describing "Topic Maps", i.e. the relations between topics and between topics and resources. I believe that XTM could have used a RDF syntax, however since it is not the case with XTM 1.0 we have to make a choice and, I think that it depends on the application you want to build and the tools you want to use. If your application is all about describing topics and relations between topics and resources you might want to use XTM and the tools that are available to build Topic Maps. On the other hand, if you want to consolidate information between applications and, for example, link your site summary with annotations and conformance tests, the generic RDF model should be much easier to use since triples from different sources do merge automatically when you load them. Developing new applications with XTM is of course possible (many papers have been published for instance to show how Topic Maps may be used to represent knowledge bases) but requires to put on "topic maps lenses" and to consider everything as Topic Map objects (i.e. topics, associations or occurrences) and that's not always very natural. The border line I would personally draw is then very simple: if you need a Topic Map, then go for XTM, but if you want something more extensible, consider using RDF. And keep in mind that if you've taken care to include enough information, you will always be able to transform RDF into XTM or XTM into RDF.

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• An Approach to the Semantic Web
  2001-05-12 13:31:53 Scott Tsao [Reply]
  
  Eric wrote:
  > I see RDF and XTM as belonging to different levels, though and
  > believe they should be more complementary than competing.
  I agree whole-heartly with you here, and my attempt was trying to
  find out WHERE they could be more complementary.

  
  > I believe that XTM could have used a RDF syntax, however since it
  > is not the case with XTM 1.0 we have to make a choice and, I think
  > that it depends on the application you want to build and the tools
  > you want to use.
  I am not sure about this. I have also heard suggestions that RDF
  model should be serialized in terms of XLink (which XTM is based
  on). My quess is that this might be a tool issue, i.e., whether
  tools are readily (and freely) available to process the serialized
  data stream.

  
  > If your application is all about describing topics and relations
  > between topics and resources you might want to use XTM and the
  > tools that are available to build Topic Maps.
  Agreed. The nice and clean separation between the topic layer and
  resource layer is a "user-friendly mental model" that helps me to
  visualize in my mind how I would want to semantically organize my
  myriad resources.

  
  > On the other hand, if you want to consolidate information between
  > applications and, for example, link your site summary with
  > annotations and conformance tests, the generic RDF model should be
  > much easier to use since triples from different sources do merge
  > automatically when you load them.
  Since I am not familiar with the details of RDF, I might be ignorant
  here. What do you mean "link your ..."? Is this the same as the
  XLink model (I thought RDF does not use XLink)? Also, you mentioned
  in various places the strength of RDF's "automatic and implicit
  merge" feature. Can you give a simple example of this? How would
  you compare it with the XTM merge feature (I believe it is part of
  the XTM Processing Model)?

  
  > Developing new applications with XTM is of course possible (many
  > papers have been published for instance to show how Topic Maps may
  > be used to represent knowledge bases) but requires to put on "topic
  > maps lenses" and to consider everything as Topic Map objects (i.e.
  > topics, associations or occurrences) and that's not always very
  > natural.
  As a matter of fact (as I stated earlier) as an user I prefer to put
  on the "topic maps lenses" (feels very natural to me). I can name a
  couple of applications that this type of lenses fit naturally:
  - controlled vocabularies (e.g., thesauri)
  - metadata registry (and repository)
  - Bible studies (as pointedly elaborated by Patrick Durusau, see
  http://groups.yahoo.com/group/xtm-wg/message/2317)

  
  > The border line I would personally draw is then very simple: if you
  > need a Topic Map, then go for XTM, but if you want something more
  > extensible, consider using RDF. And keep in mind that if you've
  > taken care to include enough information, you will always be able
  > to transform RDF into XTM or XTM into RDF.
  As an implementor, I would hope that I will not have to pay the
  panelty for this transformation. Also, I don't understand what you
  mean by "more extensible" if I use RDF. Is it because the fact that
  more tools are available (especially those advocated by the W3C)?
  From the semantic enrichment standpoint, I think XTM is more
  extensible. We are probably talking about "extensibility" at two
  different levels, which we both agreed from the start.

  
  Thanks,

  
  Scott Tsao
  The Boeing Company