lightweight reification (was Representing trust (and other contex t) in RDF)

Hi Graham
 
>Brian,
>
>What I am trying to accomplish is to find a *representation*
>(as opposed to
>implementation), within the RDF model (as opposed to
>serialization), for
>trust-related information.

This is a really interesting question.

>
>I think we may be trying to say the same thing, or something very
>similar.  Certainly, Guha's comments about representing contexts as
>resources seem entirely consistent with what I was trying to suggest.
>

I think I was saying two things mixed up in the same message.  So I'd like
to split them up to keep them separate.

>Unfortunately, I find XML serialization of RDF is very
>difficult to read,
>and not helped by the HTML formatting of your message,

I've just looked at the archive - the message didn't look like that when I
pressed the send button.  I'll have a look at my mail config and see if
there is anything I can do this end to prevent that sort of thing happening.

> so I can't tell
>exactly what you propose in your message.  It looks as if you are
>suggesting something similar to Sergey's proposal that I
>reference from my
>original posting.
>

I have a couple of different thoughts I'd like to toss into the discussion.
Lets take the one that is most similar to the digest proposal first.  The
other had better wait till I've had a read of the context stuff that Guha
and Dan have pointed us at.

At one level, the goal is to make be able to make statements about
statements, without invoking the perceived overhead of full RDF reification.

Since RDF statements can only be about about resources, then a resource is
needed that will act as a model for the statement.  The current RDF m&s
proposal is to create a resource, with 4 properties (type, subject,
predicate, object) and this seems to raise negative reactions.

My understanding of the digest proposal is to create a resource to model the
statement, but not add the 4 extra properties.  The problem is how to relate
that resource to the statement that it models.  It is  suggested to relate
the two by computing a digest of the statement and using that digest to
construct a URI for the resource that models the statement.

M&S is quite specific when it talks about reification that a statement and
the resource that models it are different things.  I haven't understood why
and I've just been wondering if one could consider statements to be
resources.

One would then have models like this:


       [this message] ---[was written by]--->Brian
                               |
                               |
                           [asserted by]
                               |
                              \ /
                             Brian


I think that this is effectively what the digest proposal does, but it seems
to me that the above is a simpler and cleaner model.  Thinking of it this
way, I don't think the digest is necessary and statements with anonymous
resources will work. 

However, the digest approach has the benefit that it can be represented by
the currently recommended syntax.
 
The final thought I'd like to add is that when I think about implementing
the non-digest approach it seems it would be easy to provide 'full
reification' with very little, if any, extra work.  So I'm left wondering
whether the 'overhead' of reification is more perceived than real.
 
Brian