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Subject: Re: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
Hello,
I think I've now understood why we cannot have
XDI documents (and possibly literals) in subjects
(i.e. to have a full addressable RDF graph).
However, with predicates like $is and their
inverse (which is $is) we should proceed
carefully. Coming back to the third example by
Kermit, if we use $is as predicate we've exactly what Kermit suggested:
<"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">
<"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";>
This is implicit in $is which MUST be symmetric
($is inverse predicate is $is). Otherwise, I
think, the semantics of $is is lost. But probably
here $is is not the best predicate...
Giovanni
At 20.57 18/03/2008, Kermit Snelson wrote:
>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!1234]]
>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!1234]]
> > 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 > $mod > / >
> =drummond > +name >
> "D.Reed" > > But you can't modify a
>subject. > > What again was a use case for
>literals in subjects? (I'm not against it, >
>just asking) > > Markus > > > On Mon, Mar 17,
>2008 at 7:34 PM, Drummond Reed
><drummond.reed@cordance.net> > wrote: > > > >
>[renaming this thread to something more
>relevant] > > > > Giovanni, > > > > I agree with
>Markus I can't make sensee of having an XDI
>document as an XDI > subject. I'm not sure my
>point from my earlier message came across, but
>I > was saying that when you use XDI context
>syntax the // syntax it does > _not_ assert
>that the previous XDDI document is the subject
>of an XDI > statement. It says that the previous
>XDI statement _contains_ another XDI >
>statement. For example, in the following X3
>Simple graph… > > > >
>=drummond > > +email > >
> / > >
> =drummond > >
> +email+home > > >
>"dsr.example@gmail.com" > >
> +email+work > > >
>"drummond.example@cordance.net" > > > > …you can
>makke the following "compound XDI
>statement": > > > >
>=drummond/+email//=drummond/+email+home > > > >
>This compound statement does not assert an XDI
>document as a subject. It > asserts the
>following: > > > > 1) =drummond is an XDI
>subject > > 2) +email is an XDI predicate of
>this subject > > 3) The object is another XDI
>document > > 4) =drummond is an XDI subject in
>this contained XDI document > > 5) +email+home
>is an XDI predicate of that XDI subject > > 6)
>"dsr.example@gmail.com" is the literal value of
>that XDI object > > > > If you wanted to have an
>entire XDI document as the subject of an XDI >
>statement, I think the syntax you are looking
>for is: > > > > >
>(xdi-subject/$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 preedicates 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 aagenda > 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%20Comments-Barnhill.pdf
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