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Re: Simpler syntax for RDF

From: Sergey Melnik <melnik@DB.Stanford.EDU>
Date: Tue, 16 Nov 1999 17:25:11 -0800
Message-ID: <383203F7.B9BB86C5@db.stanford.edu>
To: Tim Berners-Lee <timbl@w3.org>
CC: www-rdf-interest@w3.org
Tim,

in my view, there are two different perspectives to look at your
proposal:

1) on one hand, we need to be able to derive an RDF model from
"arbitrary" XML (tough issue)
2) on the other hand, a syntax that facilitates exchange of RDF between
applications is needed that is easy to understand, implement etc.

Let me start with (2) since this is the simple point. My experience
during contributing to SiRPAC and implementing serialization for RDF
suggests, that for many cases a "*poor* strawman's syntax" would be just
fine:

<triple subject="URI" predicate="URI" object="URI"/>
<triple subject="URI" predicate="URI">literal</triple>

A "desperate Perl hacker" (remember this paper?) could implement in
within minutes. You still have all the advantages of Unicode-based XML
etc.

As to (1):

there are two big problems that I see, and a number of smaller ones. The
big problems are:

(a) since parsing relies on the schema information about XML tags,
parsing without schema would not be possible (I might have misunderstood
this). In that case, however, we're moving to where we came from: SGML
is not parseable without DTDs.

(b) default context: in the current specs, the context is limited to one
level within the Description. Higher context-sensitivity (many-level) is
problematic if one needs to extract information out of context. Even in
case of nested RDF/XML you'll find just a couple of RDF pages out there,
that use it correctly.

You have made a "call for implementation". However, so many issues still
have to be resolved, that I (as a potential implementor) would just not
know where to start.

RDF 1.0 has a number of legacy, heritage or flawed features, that make
both the specification and implementation intransparent. To make my
criticism a bit more constructive, consider as examples the following
issues:

- aboutEachPrefix: if you create an RDF model using RDF/XML that
contains aboutEachPrefix, and serialize it back, the intended semantics
is lost, since this aboutEachPrefix is not reflected in the model.

- xml:lang does not appear in the model either and is therefore also a
bug in the specs. Either a new triple has to be appended to the model,
or xml:lang should be ignored.

- there is no principle difference between rdf:ID and rdf:about. There
would be one if you appended rdf:isDefinedBy to every resource defined
by rdf:ID. Not in the model - no semantics.

- ...

Before such issues have been resolved, I'd be very careful about
motivating people to implement something. Currently I am a courtesy
maintainer of SiRPAC. However, to be frank, I'm not willing to
rewrite/adapt it as long as the specs are flawed.

I like the spirit of your proposal. Still, I think that an organized
effort is needed to produce something targeted at RDF M&S 2.0. And I'd
definitely love to contribute to it.

Best,
Sergey
Received on Tuesday, 16 November 1999 20:20:35 GMT

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