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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 > > PLEASE NOTE: If the above links do not work >for you, your email application > may be >breaking the link into two pieces. You may be >able to copy and 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: > 02/02/2008 13.50 > > > > > > > >
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