W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2001

Re: Syntax vs Semantics vs XML Schema vs RDF Schema vs QNames vs URIs (was RE: Using urn:publicid: for namespaces)

From: David Allsopp <dallsopp@signal.dera.gov.uk>
Date: Wed, 15 Aug 2001 16:10:33 +0100
Message-ID: <3B7A90E9.35F0EDAF@signal.dera.gov.uk>
CC: www-rdf-logic@w3.org, www-rdf-interest@w3.org

Patrick.Stickler@nokia.com wrote:
> > >For those who are convinced that anonymous nodes are a good
> > thing, please
> > >think about the implementational burden and
> > portability/interoperability
> > >issues they may introduce.
> >
> > What burdens and issues? .
> Specifically the need to refer to resources as a template of
> property values (i.e. [X namespace '...', X name '...'])
> rather than a single opaque URI identifier.

But this is just querying - you have to do that anyway to find out what
the "opaque URI" actually is. 

And as I said previously, you have to keep generating long pseudo-unique
IDs, which may clash occasionally.

Finally, this hinders you in identifying equivalent resources when you
merge data from two sources, because the two sources have to assign a
pseudo-unique URI to the resource; a third party can't then determine
that the nodes really refer to the same thing, e.g:

John --hasFather--> [] --age--> 84

John --hasFather--> [] --age--> 84

compared with

John --hasFather--> randomgenid0123456789 --age--> 84

John --hasFather--> randomgenid9876543210 --age--> 84

where [] represents an anonymous node.

The point is that we don't know the name of John's father, so assigning
him a random name makes our life harder, not easier, since everybody
necessarily assigns him a _different_ random name.

> Another is not knowing whether I will get back from a
> query an anonymous node constituting the root of a collection,
> containing resource nodes (or other collections) rather than
> an actual resource node -- or possibly getting a set of results
> having both resource nodes *and* collection root nodes -- because
> in one case in the *serialization* the values of a property were
> defined as a bag in the "same" statement and in another case
> each was defined as a separate statement! Yuck!

I don't see how removing anonymous nodes assists here - the data can
always be structured in different ways, and you have to know that in
advance, or perform cleverness to deduce the structure.

I agree the RDF collections are rather awkward though.


David Allsopp.

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Received on Wednesday, 15 August 2001 11:10:44 UTC

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