Short Essay: Squeezing RDF into a Java Object Model
david at megginson.com
Mon May 3 20:49:11 BST 1999
W. E. Perry writes:
> David Megginson wrote:
> > Obviously, there's a much more complex model underlying RDF than the
> > spec lets on, and that model affects not only the ease or difficulty
> > of implementing an object model, but also the difficult of many
> > standard operations like queries against a collection of RDF
> > statements and storage in a relational database.
> May I respectfully submit that the problem is not the complexity of
> the model underlying RDF, but its simplicity and relative freedom
> from restriction, permitting the very sort of extension that leads
> to the implementational problems David Megginson illustrates.
I'm not certain that I follow -- I did not consider extensions at all
in my essay.
Certainly, it is possible to build complex layers on top of a simple
data model, and much of what is in the RDF-syntax spec (such as the
containers, rdf:type, rdf:value, rdf:Statement, etc.) together with
all of the RDF-schema spec can be taken in that light; as a result, I
considered none of that in my model.
The problem is that the bottom-level, primitive model required for RDF
support is itself rather complicated. It is certainly fair, in the
model, to include
but you also have to specify what a Subject, Predicate, and Object
are. They are not simply resources/URIs, but have properties of their
This is the bare-bones RDF data model, according to my reading of the
spec. Now, I will certainly admit that I have not been involved in
the RDF design process, and may have misunderstood something: I
encourage all members of XML Dev to feel free to correct me, no matter
how experienced or inexperienced they may be with RDF.
> Effectively it is just such a cumulative body of metadata which
> David Megginson is seeking. It would provide the ability to refer
> to components larger than simple subjects, predicates and objects,
> such as resources as objects or prefixes as subjects. Such a
> framework would comprehend and permit reference to any such objects
> either top-down, from the perspectives of their larger containers,
> or bottom-up from the perspective of their sub-components.
I don't think that that's what I was looking for, though it certainly
sounds interesting. Right now, I'm just considering the smallest
possible data model required for implementing the RDF-syntax
All the best,
David Megginson david at megginson.com
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