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RE: N3 contexts vs RDF reification

From: Lee Jonas <lee.jonas@cakehouse.co.uk>
Date: Wed, 25 Apr 2001 18:00:45 +0100
Message-ID: <51ED29F31E20D411AAFD00105A4CD7A77112@zingiber.cakehouse.co.uk>
To: "'Seth Russell'" <seth@robustai.net>, RDF-IG <www-rdf-interest@w3.org>
Seth Russell [mailto:seth@robustai.net] wrote:

>From: "Lee Jonas" <lee.jonas@cakehouse.co.uk>
>
>> I like the concept, but does it mean n+1 tuples? e.g.:
>> (stmtid1,p,s,o)
>> (stmtid2,references,ctx1,stmtid)
>
>Yes, but I don't see that as a problem, do you?
>

Actually, it becomes n+n*m tuples (worse-case), e.g.:

(stmtid1,p1,s1,o1)
(stmtid2,p2,s2,o2)
(stmtid3,ref,ctx1,stmtid1)
(stmtid4,ref,ctx1,stmtid2)
(stmtid5,ref,ctx2,stmtid1)
(stmtid6,ref,ctx2,stmtid2)

This bothers me ever so slightly (though not a lot): my proposal would not
fare much better at n*m:

(ctx1,p1,s1,o1)
(ctx1,p2,s2,o2)
(ctx2,p1,s1,o1)
(ctx2,p2,s2,o2)

I would have been more bothered by occurrences of what should be the same
statement being assigned different statement ids.  But your next bit means
this is not what is happening:

>> Also, you have to explicitly identify all statement occurrences
>> consistently, even across documents - this could prove yet another
problem
>> for generating valid rdf.
>
>Well actually I am not proposing any changes in RDF\XML  or the RDF data
>model whatsoever - so my proposal would have nothing to do with validating
>RDF.  Rather my proposal addresses the internal data structure of a
>application ... I guess you could call it the RDF API.
>

Ok.

>> Rather than an 'artificial key' for statements, what if the key were
>> regarded as (p,s,o)?
>> then
>> (c1,p1,s1,o1)
>> (c2,p1,s1,o1)
>> represents two contexts referring to the same statement.  The consumer of
>> statements is free to 'import' them into their own contexts if they wish:
>> (c3,p1,s1,o1).
>
>Cool!  I hadn't though of that.  In this regard our proposals are almost
>identical.  And in my application I actually do form the key p+s+o to
insure
>that a potentially new triple does not already exist before I store it in
>the database enforcing the idealistic view that triples are unique.
>

Arguably, you are storing the ephemeral statements, whereas all triples
generated from parsing the RDF/XML are *occurrences* of said statements.

>However, the extra tangible arc label assigning the triple to a context
>proves useful for other reasons in my system.  With it one can talk about a
>statement being in a context ... and that statement being in a context ...
>and so on .. and so on .. and so on.   With your system there is no such
>explicit arc of which we can speak.
>

No, but that information is captured directly in the quadruple.  I can map
quadruples into 3 tables (and vice-versa):

CREATE TABLE contexts(ID INT PRIMARY KEY);
CREATE TABLE statements(ID INT PRIMARY KEY, ...);
CREATE TABLE contexts_statements_xjoin(ContextID INT, StatementID, PRIMARY
KEY(ContextID, StatementID));

Then, I can determine which statements are in which contexts from
'contexts_statements_xjoin'.

I.e. I don't need extra statements in the RDF Model to determine context
membership, either from the quadruples or direct from the database.

I am doing something like this in a new project I am working on, so it will
be interesting to see if it works out ok.  Perhaps more on that later...

>And also I don't understand how you have solved the reification problem
....
>[previously you mention]
>> It seems to me that the goal of reification is to make further statements
>> about statements - i.e. make statements the subject or object of other
>> statements.
>
>I can see how we can use your technique to make statement(s) the subject or
>object of other statements.  But what about just one statement ?  For
>example I can say (c1,p1,s1,o1) and (c1,p2,s2,o2) and then talk about those
>with (c2,p3,c1,o3) but what if I just want to talk about the second
>statement alone .. how would I do that?
>

By creating a new context, c3, containing an occurrance of the second
statement - i.e. (c3,p2,s2,o2).


>thanks for the dialogue ...
>Seth

You're welcome.

regards
Lee
Received on Wednesday, 25 April 2001 13:00:41 GMT

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