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RE: Provenance usage scenario - releaseTime

From: Ronald Daniel <rdaniel@interwoven.com>
Date: Fri, 15 Feb 2002 21:37:33 -0800
Message-ID: <145C1D60907A4944ABAE75DE3FF6418C2C7FE1@xchanger3.interwoven.com>
To: "'fmanola@mitre.org'" <fmanola@mitre.org>
Cc: w3c-rdfcore-wg@w3.org
Frank asked:

> Could you clarify something about your example?
> > 
> >       <someArticleURI> <D:describedBy> ?M     # M is metadata record URI
> >       ?M   <prism:receptionTime>  ?Tgot
> >       ?M   <dc:source>  ?FromWho
> >       ?M   <x:contains> ?_S                   # _S is statement URI
> >       ?_S  <rdf:type>  <rdf:Statement>
> >       ?_S  <rdf:subject> <someArticleURI>
> >       ?_S  <rdf:predicate> <prism:releaseTime>
> >       ?_S  <rdf:object> ?Trel
> 
> Are you assuming that the metadata record M contains the individual
> triples that you would expect to see produced from parsing the XML/RDF
> you give initially, or does it contain a set of reification quads (the
> quads with ?_S as subject) expanded from those triples that would then
> be directly matched by the query syntax?  

The former. I assume the query processor 'knows' enough about
rdf:subject, rdf:predicate, and rdf:object to be able to answer
queries as if they are there, but there is no way I want all that
gunk cluttering up the graph.

(To digress for a moment; I actually assume M would identify a text file,
or a text string in a DB, that holds the serialized RDF that was actually
received. Reason is that it is better for the provenance application to
be able to say "here are the bits we got from you" instead of
"here are the bits we kept after we fiddled around with what you sent us".
Of course, the query engine that would have the job of searching those
files would probably have built a search index that looks astonishingly
like a triples store. But I assume it will only have the explicit triples
in it.)

> Comment:  This, I think, illustrates one of the reasons for having a
> standard vocabulary for describing statements (you can use it in
> queries).

Complete agreement.

> It's still not clear to me how the vocabulary per 
> se helps in
> recording  provenance information,

If by 'vocabulary' you mean rdf:subject,predicate,object I agree that
they do not directly have much to do with the provenance of a
statement or graph. However, being able to pick those fields out
of a statement is important so we can do the queries.

> since here the provenance is about
> the metadata record (which has a URI), not an individual reified
> statement.

Yeah, it is more around the whole metadata record than one item in it.
When I started I wanted to do a use case that would need a reified
statement, but this example kind of took off with a mind of its own.
However, it seemed important to show that there are provenance
applications that need to identify an entire incoming description,
because that has not been talked about as much as inidividual statements
but will probably be more common.


Note that the query assumes individual statements can be
identified. If they can, then we would seem to have all that is needed
for the finer-grained provenance (which I think you pointed out in an
earlier message).

So I think that for provenance we need the following:
  1) A method for identifying 'statements' in a serialized RDF document.
    (Again, don't take this to indicate any stance on Brian's 'stating'
    vs. 'statement' terminology)
     a) rdf:ID lets us ID some statements up front in the syntax
     b) We MAY need to have an agreed-upon syntax for adding IDs to
        statements ex-post-facto so that everyone can do it the same,
        but I suspect that is a 'nice to have' not really a 'must have'.
  2) A method for identifying whole graphs
  3) A method for stating that a particular statement came from a particular
     graph.

> (On the other hand, this may be close enough:  I can
> identify that a given *container* (the metadata record), 
> which does have
> a URI, contains a statement that *looks like* a given description, and
> the provenance is associated with the container as a whole.)

You are probably right, but I don't know what 'looks like' means.
Here's a quick test case to show what I'm currently assuming:

<rdf:RDF ...namespace decls...>
 <rdf:Description rdf:about="http://example.com/index.html">
  <dc:publisher rdf:ID="foo:12345">The Example Company</dc:publisher>
  <dc:creator>webmaster@example.com</dc:creator>
 </rdf:Description>
</rdf:RDF>

(Have to extend n-triples to n-quads which uses () at the front to hold
the statement URI)

 (foo:12345) <http://example.com/index.html> <dc:publisher> "The Example
Company" .
 (_:a)       <http://example.com/index.html> <dc:creator>
"webmaster@example.com" . 

A system that enabled provenance tracking would also create something like
the following graph when it imported the serialization earlier:
(the empty () at the start of these means the statements have a URI
but I didn't bother to specify it)

 () <_:m> <rdf:type> <x:RDF-serialization> .
 () <_:m> <prism:receptionTime> "2002-02-15T20:19T-8:00" .
 () <_:m> <x:contains> <foo:12345> .
 () <_:m> <x:contains> <_:a> .
 () <_:m> <dc:creator> "Jane Doe"

Here are some queries over the inital graph:

 ?X <dc:creator> ?Y
 => [
     X = <http://example.com/index.html>
     Y = "webmaster@example.com"
    ]

 ?X <rdf:predicate> <dc:publisher>      # Domain of rdf:predicate is a
Statement
 => X = <_:a>

 ?X <rdf:type> ?Y
 => empty         # This is what I would expect because there are not
explicit
                  # rdf:type statements in the graph. But this may be bad
                  # because...

 ?X <rdf:type> <rdf:Statement>
 => X = <foo:12345>
    X = <_:a>

                  # and also ...
 ?X <rdf:predicate> <dc:publisher>
 ?X <rdf:type> ?T
 => [
     X = <_:a>
     T = <rdf:Statement>
    ]

Looks like I'd prefer that the subject/predicate/object/Statement things
that are implicit are ignored until explicitly asked for in a query.

Ron
Received on Saturday, 16 February 2002 00:38:06 EST

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