Re: Comments on 'precedural approaches'

From: Emmanuel Pietriga <>
Date: Tue, 26 Apr 2005 08:20:40 +0200

Stefano Mazzocchi wrote:
> These are random comments on Section 2.1 of the current paper's working
> draft, sent here for archival and for triggering further discussion.

Also archiving my reaction to these comments.

> - xslt over RDF/XML is always possible, it's just unberably hard and
> error prone, due to the XSLT-unfriendly nature of RDF/XML.
> - "conceptually wrong" is a little big too strong, use "conceptually
> defective"? A great example is the fact that rdf:type="blah" can become
> the element name, modelling this in XPath is extremely hard.

I really feel strongly against this RDF/XML+XSLT as a general approach
for transformaing RDF. That's why I put "wrong". But you're right,
that's probably too strong... The example is a good one and we should
probably cite it. But it is more an illustration of the point above
(unbearably hard) than of this one (conceptually defective).

> - the other problem with XSLT is the notion that it acts as a
> transformation filter on a given infoset. In theory, this infoset could
> be as big as the whole triple store model itself, in practice however,
> due to the intrinsic nature of XSLT recursivity, it is ill suited for
> 'selection by filtering'.


> - mention XQuery as a potential alternative to the above, but note that
> it suffers from the same problems as XSLT.
> - "potential irregularit, openness and use of different vocabularies"
> this is not true. XSLT can cope with that too.

Yes it can. But at what cost? The complexity is so huge... Again, that's
why I believe the RDF/XML+XSLT approach to be conceptually wrong.
Addressing RDF at the lower level of abstraction that is its RDF/XML
representation makes it so difficult. Yes, there are a lot of useful
tools for processing XML, but it does not mean that they are suited to
processing RDF models.

> The problem is not that
> is the fact that we have graphs instead of trees and all existing
> technologies work with trees, not graphs.

Yes. But it is not just that. It is the fact that the RDF/XML tree is
intended for the serialization of the RDF model. It is just one possible
projection of the graph, and it thus looses the generallity found at the
RDF graph level.

My point is that it is not just a question of processing graphs or trees
with the right tools, it is also a question of how the data is
structured and represented. When presenting people with the RDF/XML tree
representation of a model, you force them to build a mental
representation of the RDF/XML tree and to map/convert it to what it
actually "means" at the more abstract (purely) RDF level. This is a hard
mental operation which requires a lot of *unnecessary* cognitive effort.
Here, it is more the HCI research scientist part of myself who talks,
but I believe this to be something that should be taken into account.

Emmanuel Pietriga
INRIA Futurs - Projet In Situ    tel : +33 1 69 15 34 66
Bat 490, Université Paris-Sud    fax : +33 1 69 15 65 86
91405 ORSAY Cedex  
Received on Tue Apr 26 2005 - 06:21:44 EDT

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