Re: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8 Commen

Subject: Re: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8 Comments-Barnhill.pdf) uploaded

On Sat, Mar 15, 2008 at 1:39 PM, Giovanni Bartolomeo <giovanni.bartolomeo@uniroma2.it> wrote:

At 20.52 13/03/2008, Drummond Reed wrote:

Giovanni,

It's a subtle point, but when you use subcontext syntax (//), the parent XDI document is not the subject of the child XDI document. It is the container ("context") for the child. Thus I don't think the ABNF should change.

Ok, I see; so if my understanding is correct, we have both the possibility to have a whole XDI document as an RDF object as well as a "contained" object ("subcontext"). Thus, the original question: in these ABNF excerpts, how could we specify that a subject can be an XDI document? E.g.

X3 = *( "[" sub *( "[" pred *( "[" obj "]" ) "]" ) "]" )
~~sub = [ comment ] xri-reference [ comment ]~~
sub = [ comment ] (xri-reference / X3) [ comment ]
pred = [ comment ] xri [ comment ]
obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]
literal = """ *char """
comment = "<--" *c-char "-->"

RE the question of whether to allow a literal as an XDI subject, yes, I have thought about, for reasons which I'll explain on today's call (if we have time).

I would allow this; especially if we'll standardize inverse predicates, we should allow a subject to be a literal, as well as a XDI document or a xri-reference.

RE whether a predicate should be able to be an XDI document, my immediate answer is no – RDF predicates are strictly URIs; XDI predicates should be strictly XRIs.

Yes, I agree with this. To summarize, I would be in favour of having the same definition for subjects and objects:

sub = [ comment ] (xri-reference / literal / X3) [ comment ]
pred = [ comment ] xri [ comment ]
obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]

what do you think?

Thanks,
Giovanni

Talk to you shortly,

=Drummond

From: Giovanni Bartolomeo [ mailto:giovanni.bartolomeo@uniroma2.it]
Sent: Thursday, March 13, 2008 3:11 AM
To: Drummond Reed; 'Markus Sabadello'
Cc: barnhill_william@bah.com; xdi@lists.oasis-open.org
Subject: RE: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8 Comments-Barnhill.pdf) uploaded

Hello Drummond,

Thanks for this clarification; however, if my understanding is correct, this means that an XDI document can also be subject of another XDI document, other than object.
Doesn't this implies that we should update ABNF syntax making the definition of subject somehow similar to the one for object?

X3 = *( "[" sub *( "[" pred *( "[" obj "]" ) "]" ) "]" )
~~sub = [ comment ] xri-reference [ comment ]~~
sub = [ comment ] (xri-reference / X3) [ comment ]
pred = [ comment ] xri [ comment ]
obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]
literal = """ *char """
comment = "<--" *c-char "-->"

Further questions are:

        should allow literals as a subject?
        should be predicate definition similar to subject and object one update, e.g. may a predicate contain an XDI document?

however I'm not quite convinced with these last two ideas... comments welcome!

Giovanni

At 22.38 12/03/2008, Drummond Reed wrote:

Just to be clear, the "n-segment" syntax was deprecated in the V9 XDI RDF Model document ( http://wiki.oasis-open.org/xdi/XdiRdfModel) due to the problems identified in this thread. To be precise, it was unclear whether

s1
            p1
                        o1
                                    p2
                                                o2

meant that s1/p1/o1 was the subject of p2/o2 or not. It was also unclear how cross-reference syntax would be applied.

We solved both problems by eliminating "n-segment" syntax in the V9 document. Now it should be unambiguous that if you want to express that s1/p1/o1 is the subject of p2/o2, you say:

            (s1/p1/o1)/p2/o2

What did remain is the // syntax for subcontexts, which allows you to solve the RDF "blank node problem" by providing an address for a blank node. That address is simply // (which fits very nicely from a conceptual standpoint since the identifier for that segment is "blank").

So if I want to say that the object of s1/p1 is a blank node, I can write it as s1/p1// . This creates a new XDI context in which I can express another set of XDI statements whose XRIs are unique in this context.

We'll go over the practical uses for this on the call tomorrow – agenda coming out shortly.

=Drummond

From: markus.sabadello@gmail.com [ mailto:markus.sabadello@gmail.com] On Behalf Of Markus Sabadello
Sent: Wednesday, March 12, 2008 10:44 AM
To: Giovanni Bartolomeo
Cc: barnhill_william@bah.com; xdi@lists.oasis-open.org
Subject: Re: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8 Comments-Barnhill.pdf) uploaded

To be honest, I don't really understand the N-Segment syntax anyway.

Why is

s1
        p1
                 o1
                          p2
                                   o2

better than

s1
        p1
                 o1
o1
        p2
                 o2

?

Markus
On Tue, Mar 11, 2008 at 4:29 PM, Giovanni Bartolomeo < giovanni.bartolomeo@uniroma2.it> wrote:
Dear Bill, All,

reading your comments about XDI RDF v8 ( http://www.oasis-open.org/committees/download.php/27112/XDI%20RDF%20v8%20Comments-Barnhill.pdf ) I've found this sentence:

One problem with the 3-Segment syntax is that the N-Segment syntax uses cross-references for
reification. This means 3-Segment syntax has to have a different notation for a subject which is the
statement itself rather than the object of the statement. The 3-Segment notation for this is a crossreference
within a cross-reference: (()). So a subject of (s/p/o) asserts s/p/o and starts a new statement
whose subject is o, while a subject of ((s/p/o)) asserts s/p/o and starts a new statement whose subject is
the statement s/p/o. For example to say that =Drummond is author of the statement =Bill.Barnhill is a
contributor to the resource represented by @example we would use the XRI:
((@example/+dc+contributor/=Bill.Barnhill))/+dc+author/=Drummond.

Well, I'm wondering how N3 syntax (and consequently X3 simple) addresses this problem:

If my understanding is correct, the N3 syntaxt
<s1> <p1> <o1>
<o1> <p2> <o2>
is equivalent to X3 simple
s1
        p1
                 o1
                          p2
                                   o2
what if I want to express that the whole statement <s1> <p1> <o1> is the subject of <p2> <o2>? How this can be represented with X3 Simple?
Breaking into a new subcontext doesn't seem to help, as this explicitly introduce a new subject!
s1
        p1
                 /
                          s2
                                   p2
                                            o2
Whereas I just want that the whole statement (s1/p1/o1) is the subject of p2!

What do you think? Am I missing something?

Thanks,
Giovanni

At 11.06 07/02/2008, barnhill_william@bah.com wrote:

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