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   Re: A certain difficulty

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  • From: "Perry A. Caro" <caro@Adobe.COM>
  • To: David Megginson <david@megginson.com>
  • Date: Fri, 25 Feb 2000 11:02:28 -0800

David Megginson wrote:
> it
> turns out that there are at least six components (not three) in each
> statement:
>   subject
>   subjectType (global id, local id, URI pattern)
>   predicate
>   object
>   objectType (literal text, literal XML markup, reference)
>   objectLang
> These are not simply syntactic artifacts -- it's information that
> *must* be exposed through any RDF API, and thus, part of the core
> model, independent of the peculiarities of the XML markup (note that
> I'm assuming that bagID, etc. are predigested).

Hear, hear!  It's misleading to talk about Statements as "simple" triples. 
They are either triples where each member is a complex object with various
attributes, or they are N-tuples of several fields, some of which are
optional or default.

By the way, you forgot "objectWhiteSpace", a field like objectLang, whose
value is either "default" or "preserve".  This is crucial to correctly
handling the xml:space global attribute.

> The URI patterns
> (aboutEachPrefix), especially, make it much trickier to do any
> relational database implementation of RDF, since you the set of
> possible subjects is open.

Again, hear, hear!  I find aboutEachPrefix to be one of the most disturbing
features of RDF.  It's value to the Semantic Web is clear, particularly for
site maps, but for offline or non-HTTP-server-mitigated metadata
applications, it is a tremendous burden.

I think Jeff Sussna made some excellent points, too.  The feedback I've
gotten from various parties who have considered using RDF matches Jeff's
concerns.  Add to Jeff's the concern that the complexity of the RDF spec
invites subsetting (I wanted to write "incites" in place of "invites").  For
example, I'm omitting support for aboutEachPrefix in version 1.0 of my
offline-oriented RDF processor.


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