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Subject: Re: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
That's an excellent point, Giovanni. My own conclusion from your observation, however, is that the change introduced in XDI/RDF V9 that made $is reflexive and therefore eliminated $a$is as inverse was a mistake and should be repealed. The fact that RDF describes a directed graph, together with the fact that a subject is not the same thing as an object, leads me to believe that it's not meaningful to have reflexive (i.e., bidirectional) predicates in RDF. =Kermit On 3/19/08, Giovanni Bartolomeo <giovanni.bartolomeo@uniroma2.it> wrote: > 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 > > > > > > > > > > > > > --------------------------------------------------------------------- > To unsubscribe from this mail list, you must leave the OASIS TC that > generates this mail. You may a link to this group and all your TCs in OASIS > at: > https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php > >
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