[Tdwg-tag] RDF versus GML; old but relevant (?)

Roger Hyam roger at tdwg.org
Sun Feb 12 19:39:08 CET 2006

Hi Stan,

As I have said before their is much merit in expressing some 
biodiversity data in GML but not committing to do everything with it. We 
would end up having to port whatever vocabularies we come across to GML 
application schemas.

There is also merit in expressing OGC 'stuff' that is of interest to us 
as an RDF compatible vocabulary so that we can embed it in things that 
are chiefly not about location. Some examples:

    * If you call a LSID for a willow specimen the metadata for that
      specimen will be in RDF and it may need to contain information
      about how it has been georeferenced. The georeferencing concepts
      are probably all OGC 'objects' but expressed as RDF. You don't
      want to have to understand GML just because you are handling data
      that is OGC compliant. Your interest may be in sequencing the
      specimen not mapping it.
    * If you call for an analysis of distribution patterns among 200,000
      willow specimens then you probably want to do it in a
      geographic-centric way (possibly GML) and also express some basic
      taxonomic info in there like their names.
    * If you want to get a description of the differences between
      species of willow so you can link it to the gene expression work
      you are doing in the lab you probably don't want it to have
      anything at all to do with GML.

So it is "horses for courses" rather than GML with everything.

Darwin Core is simple enough as a vocabulary that it will probably be 
expressible in many forms.

Does that make sense?


Blum, Stan wrote:
> I (we) desperately need to solve the puzzle of how to compose (re-use) 
> conceptual specifications.  Can we create a flexible system of base 
> classes that can be snapped together to make useful data exchange 
> applications?  I think this is one of, if not THE most import tasks 
> for the incipient TDWG Architecture group.
> So I'm trying to educate myself about RDF versus XML (and their 
> respective schema tools).  I came across this comment on RDF versus 
> GML, http://www.mapbureau.com/gml/, which contained this:
> <excerpt>
> [...] GML is not directly composable with other XML languages. 
> Entities that are described by other languages cannot legally play the 
> role of geographic features in GML. This because all types of 
> geographic features are required to derive from the GML abstract class 
> *gml:AbstractFeatureType*. Even if it were not for this formal 
> requirement, the lack of conventions about how to represent even 
> simple semantic notions in XML languages would prevent effective 
> integration of GML with XML languages developed independently.
> The non-composability of GML requires that it absorb as application 
> schemas the multitude of other domains to which geographical 
> information is relevant. Failing this, non-standard mechanisms of some 
> kind must be used to relate GML content with external data.
> Indeed, GML positions itself as a universal, rather than 
> geography-specific, semantic standard by including its own general 
> formalisms for collections, assertion of properties (in a style very 
> much like RDF), time and processes, and reference between content in 
> separate files (via Xlink). GML can be viewed as an alternative not 
> just to geography in RDF, but to RDF itself.
> </excerpt>
> This seems like a problem for us because some aspects of our 
> biodiversity information are decidedly not spatial.  Is this a problem 
> with XML Schema generally or just the way it was used to create GML?  
> Several TDWGers are getting enthusiastic about RDF, despite the 
> cautions of McCool (referenced by Bob Morris earlier on the TDWG-GUID 
> list).  Should we go ahead and cast DarwinCore as a GML application 
> while we gear up for a coordinated switch to RDF?
> -Stan
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 Roger Hyam
 Technical Architect
 Taxonomic Databases Working Group
 roger at tdwg.org
 +44 1578 722782

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