RDF Question: about syntax of rdf container objects (Bag, Alt, Seq)

Dan Brickley Daniel.Brickley at bristol.ac.uk
Thu Apr 8 18:34:18 BST 1999

[ Can we drop www-rdf-comments at w3.org from the cc: list now? ]

On Thu, 8 Apr 1999, Walter Underwood wrote:

> At 04:51 AM 4/8/99 -0700, Jeffrey E. Sussna wrote:
> >No. RDF defines alternative syntax for particular abstract models. You may
> >use whichever syntax you like. The examples you included are equivalent.
> >This is part of both the flexibility and seeming difficulty at first glance
> >of RDF.
> It isn't a "seeming" difficulty, it is a real problem. Two syntaxes
> are much, much less useful than one. Having two or more ways to say 
> the same thing (zip, jar, and cab for Java) is almost always a bad
> idea. The reason given for the compressed RDF syntax, "it's smaller",
> is never a good enough reason. Either use the small one, use the clear 
> one, or make one that is small enough and clear enough. Specs are
> the wrong place to prevaricate.

It's not really two syntaxes, since all syntactic variants are part of
the RDF syntax specification. 

(as a side thought: if someone proposed a way of mapping arbitrary XML
content into the RDF directed-labelled-graph data model (eg. by
interpreting schemas or through XSL) would people complain that this
made RDF even more syntactically flexible?)

RDF is explicitly in the business of providing a common data model
across multiple applications, and this includes PICS labels, embedded
metadata in images and other obscure ways of shipping around statements
about the properties of various Web objects. So multiple ways of
discovering facts to store using the RDF data model is pretty much
inevitable. A web indexing application for example might want to store
RDF summaries of PDF files, PICS labels, HTML and XML docs, JPEG, GIF
and PNG images. For there to be a single 1:1 mapping of RDF into a
concrete syntax would pretty much squish the point of having it in
first place. 
All that said, there is a better justification for RDF's syntactic
flexibility than that of size: we need to be able to shove this stuff
into the heads of normal Web documents without having it leak out in
older browsers, hence the string-properties-as-attributes variant of
the syntax.


Daniel.Brickley at bristol.ac.uk                  
Institute for Learning and Research Technology http://www.ilrt.bris.ac.uk/
University of Bristol,  Bristol BS8 1TN, UK.   phone:+44(0)117-9287096

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