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Subject: RE: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
Kermit, I agree with you that RDF itself doesn't allow literals as subjects
(why they made that decision is a topic we'll put out of scope for now).
However I doesn't make sense to me that the "proper XDI mapping" of the HTML
link...
Blah blah <a href="http://example.com/some/target";>some literal text
here</a> blah blah
...would be:
XDI subject = "http://example.com/some/target";
XDI predicate = $html$a
XDI object = "some literal text here"
The reason is that I don't think that's the actual RDF graph being
expressed. An HTML link embedded in one page pointing to another Web page
would be the following graph:
---------------------- -----------------------
| HTML link text | ======> | Target page |
---------------------- -----------------------
RDF subject RDF predicate RDF object
That would map to:
XDI object = "some literal text here"
XDI predicate = $uri
XDI subject = "http://example.com/some/target";
However, building on Markus' suggestion, it does appear that there is a
clean way to express this so that it does not force us to have a literal as
an XDI subject. In X3 Simple, it would be the following:
$
$type$xsd$string
"some literal text here"
$uri
"http://example.com/some/target";
This especially makes sense since "$" by itself represents the self-context
-- literally, "here and now", which is what every HTML link actually
represents -- a link from the point where you see the link to the target
resource. So in English-pseudo-X3 this would translate to something like:
In the current context
the text
"some literal text here"
has the URI
"http://example.com/some/target";
That completely solves the problem. We still get unambiguous HTML-to-XDI-RDF
translation of any HTML link together with the ability to extend the
semantics of the link as we discussed earlier in the thread. So a corrected
example of such a "rich XDI link" we discussed earlier in the thread would
be:
Blah blah [$[$type$xsd$string["some literal text here"]
[$uri["http://example.com/some/target";]]
[$uri$https["https://example.com/some/target";]]
[$is[@!F83.62B1.44F.2813!1234]] blah blah
=Drummond
> -----Original Message-----
> From: kermit.snelson@gmail.com [mailto:kermit.snelson@gmail.com] On Behalf
> Of Kermit Snelson
> Sent: Tuesday, March 18, 2008 12:58 PM
> To: Drummond Reed
> Cc: Markus Sabadello; Giovanni Bartolomeo; barnhill_william@bah.com;
> xdi@lists.oasis-open.org
> Subject: Re: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-
> Barnhill)
>
> There are at least three reasons, in my opinion, why XDI/RDF subjects
> can't be literals:
>
> 1) RDF itself doesn't allow literals as subjects:
>
> http://www.w3.org/TR/rdf-concepts/#dfn-subject
>
> 2) The proper XDI mapping of:
>
> Blah blah <a href="http://example.com/some/target";>some literal text
> here</a> blah blah
>
> would be:
>
> XDI subject = "http://example.com/some/target";
> XDI predicate = $html$a
> XDI object = "some literal text here"
>
> and the corresponding inline X3, with the additional predicates in
> Drummond's example, would be something like:
>
> Blah blah [http://example.com/some/target[$html$a["some literal text
> here"]]
> [$uri$https[https://example.com/resolvable/uri]][$is[@!F83.62B1.44F.2813!1
> 234]]
> blah blah
>
> 3) Allowing literals as subjects doesn't make logical sense. Consider
> the following:
>
> <"http://example.com/number/of/hours/in/a/day";>
> <http://english.com/is";> <"24">.
> <"http://example.com/number/of/beers/in/a/case";>
> <http://english.com/is";> <"24">.
>
> So far, so good. But to assert the following:
>
> <"24"> <"http://english.com/is";>
> <"http://example.com/number/of/hours/in/a/day";>.
> <"24"> <"http://english.com/is";>
> <"http://example.com/number/of/beers/in/a/case";>.
>
> is to assert some substantial connection between the number of hours
> in a day and the number of beers in a case, which is fallacious.
>
> =Kermit
>
> On 3/18/08, Drummond Reed <drummond.reed@cordance.net> wrote:
> >
> >
> >
> >
> > First, let me be clear: I'm not a big fan of using literals as subjects,
> and
> > I don't have any compelling use cases for it (see below for the only one
> > I've been thinking about). It was Giovanni who seemed to have a reason
> for
> > using literals as subjects.
> >
> >
> >
> > Second, I agree, a literal as a subject can't be changed or it becomes a
> new
> > subject from an XDI standpoint.
> >
> >
> >
> > Now, here's the one thing that's had me thinking about literals-as-
> subjects
> > for a long time - take a standard HTML link tag:
> >
> >
> >
> > Blah blah <a
> > href="http://example.com/some/target";>some literal text
> > here</a> blah blah
> >
> >
> >
> > If you wanted to turn this into an XDI statement, the only logical
> mapping
> > that seems to make sense is:
> >
> >
> >
> > XDI subject = "some literal text here"
> >
> > XDI predicate = $uri
> >
> > XDI object = "http://example.com/some/target";
> >
> >
> >
> > In other words, were you to replace HTML <a> tags with X3 within an HTML
> > document, the above link would look like:
> >
> >
> >
> > Blah blah ["some literal text
> > here"[$uri["http://example.com/some/target";]]] blah blah
> >
> >
> >
> > That's pretty cool, because now you have a way of embedding really rich
> > semantics into ordinary web pages and web links. As a simple example,
> image
> > being able to make the above simple link into a compound statement,
> which
> > includes: a) an alternate HTTPS URL for the target resource, and b) a
> > persistent XRI synonym for the resource:
> >
> >
> >
> > Blah blah ["some literal text
> > here"[$uri["http://example.com/some/target";]]
> >
> [$uri$https["https://example.com/some/target"]][$is[@!F83.62B1.44F.2813!12
> 34]]
> > blah blah
> >
> >
> >
> > Net net: it's the ability to put XDI statements inline in ordinary HTML
> and
> > other markup formats that's the strongest use case I've seen so far for
> > being able to treat literals as XDI subjects.
> >
> >
> >
> > =Drummond
> >
> >
> >
> >
> >
> >
> > ________________________________
> >
> >
> > From: markus.sabadello@gmail.com [mailto:markus.sabadello@gmail.com] On
> > Behalf Of Markus Sabadello
> > Sent: Tuesday, March 18, 2008 9:30 AM
> > To: Drummond Reed
> > Cc: Giovanni Bartolomeo; barnhill_william@bah.com; xdi@lists.oasis-
> open.org
> > Subject: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-
> Barnhill)
> >
> >
> >
> >
> >
> > One aspect that seems strange with using literals as subjects is that
> you
> > can't modify them with XDI messages (I think).
> >
> > If you have
> >
> > =drummond
> > +name
> > "Drummond"
> >
> > You can modify the literal like this:
> >
> > =drummond
> > $mod
> > /
> > =drummond
> > +name
> > "D.Reed"
> >
> > But you can't modify a subject.
> >
> > What again was a use case for literals in subjects? (I'm not against
> it,
> > just asking)
> >
> > Markus
> >
> >
> > On Mon, Mar 17, 2008 at 7:34 PM, Drummond Reed
> <drummond.reed@cordance.net>
> > wrote:
> >
> >
> >
> > [renaming this thread to something more relevant]
> >
> >
> >
> > Giovanni,
> >
> >
> >
> > I agree with Markus - I can't make sense of having an XDI document as an
> XDI
> > subject. I'm not sure my point from my earlier message came across, but
> I
> > was saying that when you use XDI context syntax - the // syntax - it
> does
> > _not_ assert that the previous XDI document is the subject of an XDI
> > statement. It says that the previous XDI statement _contains_ another
> XDI
> > statement. For example, in the following X3 Simple graph.
> >
> >
> >
> > =drummond
> >
> > +email
> >
> > /
> >
> > =drummond
> >
> > +email+home
> >
> >
> > "dsr.example@gmail.com"
> >
> > +email+work
> >
> >
> > "drummond.example@cordance.net"
> >
> >
> >
> > .you can make the following "compound XDI statement":
> >
> >
> >
> > =drummond/+email//=drummond/+email+home
> >
> >
> >
> > This compound statement does not assert an XDI document as a subject. It
> > asserts the following:
> >
> >
> >
> > 1) =drummond is an XDI subject
> >
> > 2) +email is an XDI predicate of this subject
> >
> > 3) The object is another XDI document
> >
> > 4) =drummond is an XDI subject in this contained XDI document
> >
> > 5) +email+home is an XDI predicate of that XDI subject
> >
> > 6) "dsr.example@gmail.com" is the literal value of that XDI object
> >
> >
> >
> > If you wanted to have an entire XDI document as the subject of an XDI
> > statement, I think the syntax you are looking for is:
> >
> >
> >
> >
> > (xdi-subject/$context$xdi)/xdi-predicate/xdi-object
> >
> >
> >
> > In this XDI statement:
> >
> >
> >
> > 1) (xdi-subject/$context$xdi) is a cross reference that uniquely
> identifies
> > an XDI document:
> >
> > a) xdi-subject is the XDI subject authoritative for a
> reference
> > to the XDI document
> >
> > b) $context$xdi is the context type
> >
> > 2) xdi-predicate is the XDI predicate whose subject is the entire
> previous
> > cross-reference
> >
> > 3) xdi-object is whatever the XDI object is (literal, another XDI
> subject,
> > or another XDI document)
> >
> >
> >
> > ****************
> >
> >
> >
> > As for the issue of whether a literal can be an XDI subject, my primary
> > concern about that is how to treat it under XDI addressing rules. In
> every
> > XDI context, the XRIs must be unique. So there are two directions we
> could
> > take:
> >
> >
> >
> > 1) Allow literals to be XDI subjects, but ignore them from an XDI
> addressing
> > perspective (i.e., they would be "invisible" from an addressing
> standpoint.)
> >
> >
> >
> > 2) Allow literals as XDI subjects in syntax, but for addressing
> purposes,
> > have a specified transformation into relative XRI. For example:
> >
> >
> >
> > ["Drummond Reed"[+email[""dsr.example@gmail.com"]]] <==X3 with literal
> as
> > non-addressable subject
> >
> > [%44rummond%20%52eed[+email[""dsr.example@gmail.com"]]] <==X3 with
> literal
> > as addressable XRI subject
> >
> >
> >
> > Thoughts?
> >
> >
> >
> > =Drummond
> >
> >
> >
> >
> >
> >
> > ________________________________
> >
> >
> > From: markus.sabadello@gmail.com [mailto:markus.sabadello@gmail.com] On
> > Behalf Of Markus Sabadello
> > Sent: Monday, March 17, 2008 9:10 AM
> > To: Giovanni Bartolomeo
> > Cc: Drummond Reed; 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
> >
> >
> >
> >
> > From the standpoint of having already implemented this, the proposal of
> > allowing a subject to be an XDI document (aka subcontext aka inner
> graph) is
> > a nightmare..
> >
> > I can think of at least the following immediate problems:
> > - Some of the serialization formats may not be able to express this.
> > - We always said that subjects in a graph must be unique. Can this
> still be
> > enforced with inner graphs as subjects?
> > - What will XDI messages look like that make changes to these subjects?
> >
> > I don't feel too secure about allowing literals as subjects either, but
> I
> > can't really argue why at this point..
> >
> > But I'm just thinking loud.. Of course all this is not necessarily a
> reason
> > not to do it :)
> >
> > Markus
> >
> >
> > 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:
> >
> > The document named XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8
> > Comments-Barnhill.pdf) has been submitted by Mr. William Barnhill to the
> > OASIS XRI Data Interchange (XDI) TC document repository. Document
> > Description: View Document Details:
> > http://www.oasis-
> open.org/apps/org/workgroup/xdi/document.php?document_id=27112
> > Download Document:
> > http://www.oasis-
> open.org/apps/org/workgroup/xdi/download.php/27112/XDI%20RDF%20v8%20Commen
> ts-Barnhill.pdf
> > PLEASE NOTE: If the above links do not work for you, your email
> application
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> paste
> > the entire link address into the address field of your web browser. -
> OASIS
> > Open Administration No virus found in this incoming message.
> > Checked by AVG Free Edition.
> > Version: 7.5.516 / Virus Database: 269.19.19/1256 - Release Date:
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> >
> >
> >
> >
> >
> >
> >
> >
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