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Re: Statements/Reified statements

From: Sergey Melnik <melnik@db.stanford.edu>
Date: Wed, 22 Nov 2000 13:52:50 -0800
Message-ID: <3A1C4032.E7AAB84C@db.stanford.edu>
To: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
CC: ML RDF-interest <www-rdf-interest@w3c.org>
Pierre-Antoine CHAMPIN wrote:
> ...
> First, Statements and Reified statements are not the same thing.

Although this is consistent with the spec, I believe there are
significant advantages both for understanding and manipulating reified
statements if these two notions are merged into one.

Can you (or anyone) list some use cases where it is beneficial to make
this distinction? I can think of several cases, in which distinguishing
statements vs. reified statements makes things a lot more complicated.
Just consider a database query that retrieves all assertions made about
a statement (by anyone).

The M&S spec clearly states that statements are *non-atomic* entities in
the RDF model, i.e. they have 3 identifiable parts. Why then getting
into trouble of defining another mechanism ("quad reification") for
identifying these same parts in a less efficient (in all senses) manner?

Consider a mathematical model for RDF: given an entity S we will always
be able to tell whether S is a statement or not (by testing whether S is
a member of set "Statements"). Given that S is a statement we will
always be able to gets its subject, predicate and object (e.g. we refer
to such X that there exist Y and Z with S=(X, Y, Z)). Thus we can pretty
safely assume that any RDF API or storage facility will provide similar
capabilities.

The "fix" or interpretation I advocate is the following:

- STATEMENTS ARE RESOURCES (that implies that every statement is unique
and equivalent to reified statement)
- toss "quad" reification mechanism altogether

If someone chooses to reply to this posting, please be constructive. If
you claim reification should be done in this or other way, justify you
opinion, or tell what the drawbacks of the above suggestion are. There
are many ways to express the same thing which are all theoretically
equivalent. However, we have to store reified statements, send them over
networks and use in query processing. Keep that in mind.

Sergey
Received on Wednesday, 22 November 2000 16:35:01 GMT

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