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Subject: RE: [xdi] XDI graph as XRIs
Bill Barnhill Associate (XML, Emerging Technologies, Web Services, Java, Ruby) Booz | Allen | Hamilton mailto:barnhill_william@bah.com phone:+1.315.330.7386 // +1.315.491.6765 (cell) i-name: xri://=Bill.Barnhill
Hi Bill, Not knowledgeable on RDF discussions, I am not quite in a position to assess the statement in 1), and would appreciate if you can explain the issue a little more so that I can get up-to-speed. For 2), what kind of encoding scheme do you propose? In case of RDF, since it essentially is an XML, we could have 0x10 0x13 in it, but for XRI, I do not think it is feasible. I guess we would have to develop an escaping scheme for line folding also. =nat Barnhill, William [USA] wrote: > > Regarding the items you listed as possible disadvantages: > 1) The difference between a literal and a reference is not so clear; > literals are not first-class objects in the graph > I think this is actually a good thing, it means you can say everything > that is a first class object in the graph is an XRI. It also allows us > to circumvent some of the issues with literals that RDF has run into. > I recently had a round (or 4) with that while working with the > Semantic Web Rule Language (SWRL). > > 2) Encoding is required for literals that contain characters not > allowed in XRI syntax > Yes, and that's a pain, but is also required for literals in RDF. For > example you have to XML escape any literals with containing XML in > RDF, unless you're using RDF/XML (and even then the support for > rdf:parseType="Literal" varies. > > You brought up two good points, but because of the above reasons I > still think literals as XRIs are 'a good thing'. > > Bill > -----Original Message----- > From: Markus Sabadello [mailto:markus.sabadello@gmail.com] > Sent: Tue 5/20/2008 3:33 PM > To: Barnhill, William [USA] > Cc: Giovanni Bartolomeo; Drummond Reed; Bill Barnhill; Nat Sakimura; > tatsuki@nri.com; xdi@lists.oasis-open.org > Subject: Re: [xdi] XDI graph as XRIs > > It seems to me the advantages of your way of doing literals are: > - An XDI graph can easily be expressed as a set of XRIs > - Predicates can have more than one literal > - Subjects can be literals > > The disadvantages maybe are: > - The difference between a literal and a reference is not so clear; > literals are not first-class objects in the graph > - Encoding is required for literals that contain characters not > allowed in XRI syntax > > Also, I'm not sure what to think about having the type in the literal > instead of in the predicate. > > Markus > > > On Tue, May 20, 2008 at 10:31 AM, Barnhill, William [USA] > <barnhill_william@bah.com> wrote: > > > > Comments inline... > ________________________________ > > From: Markus Sabadello > Sent: Tue 5/20/2008 12:20 PM > To: Barnhill, William [USA] > Cc: Giovanni Bartolomeo; Drummond Reed; Bill Barnhill; Nat > Sakimura; tatsuki@nri.com; xdi@lists.oasis-open.org > > Subject: Re: [xdi] XDI graph as XRIs > > > > I have seen the type in the predicate many times. > > E.g. would this > > =bill.barnhill > +email$xsd$string > "barnhill_william@bah.com" > > be the same as this? > > =bill.barnhill > +email > $xsd$string*' > <mailto:$xsd$string*%27barnhill_william@bah.com%27> > barnhill_william@bah.com' > > {wab: > Not sure, depends on what you mean by 'same', but I think the > answer to what you mean is yes. > } > > Could you even still call the second example a "literal"? > Looks like it would just be an XRI segment like everything else? > > {wab: > Yep, Exactly! That's why I said in my earlier email I prefer > the approach of not having literals at all (like Drummond says), but > still being able to capture the semantics that literals imply by > having literals just be another type of XRI. What do you think? > } > > Markus > > > On Tue, May 20, 2008 at 4:24 AM, Barnhill, William [USA] > <barnhill_william@bah.com> wrote: > > > Hope this gets through to the list. > > > Thank you Giovanni for bringing up the typing point. > For typing I've been treating 'xxx' as a subsegment that represents an > untyped literal that defaults to the string type $xsd*string (also > seen it in emails as $xsd$string, but am now liking first method > better to avoid namespace clutter). > > I'm using the idea that any literal is a name within > the namespace consisting of all literals, and a typed literal is a > name within the sub-namespace of literals that is the namespace > consisting of all literals of that type. > > '11' then translates to $xsd*string*'11' > > and the number 11 as an integer literal would be > $xsd*integer*'11'. > > Thanks, > > Bill > > > ________________________________ > > From: Giovanni Bartolomeo > Sent: Tue 5/20/2008 6:08 AM > To: Markus Sabadello; Drummond Reed > Cc: Bill Barnhill; Nat Sakimura; tatsuki@nri.com; > xdi@lists.oasis-open.org > Subject: Re: [xdi] XDI graph as XRIs > > > Guys, welcome back from the Summit! > > I'm reporting some excerpts from one of Bill's mail > (it was about to allow literals as subject): > > > > [..] Post is long so won't reproduce it here, > but I strongly urge a read for anyone interested in this issue. To me > the arguments in that post, and those made on the list here, put me > firmly on the side of allowing literals as subjects. > > But it poses a further question: How do we > represent them? Do we allow 24 and "xx" as literals or only "24" and > "xx"? Furthermore if all subjects are XRIs (and I think they should > be), how is a literal an XRI? > > What is a literal? It could be viewed as a > name in the namespace context of it's type. So if we pick one of the > following we can treat all literals as XRIs: > a. There is an open class of dollar words that > start with $" and end with ", e.g. $"24", $"foo" that represent > untyped literals, and you represent a typed literal via either > $xsd.int <http://xsd.int/> *$"24" or $"24"/$isa/$xsd.int <http://xsd.int/> > b. The class of literals is a special class of > xrefs that begin with a quote after the opening paren and end with a > quot before the closing paren. This has the benefit of making all > literals relative to context, but detriment of making typing require $isa. > > > if we follow this suggestion, any literal will have a > counterpart represented by a valid XRI, thus storing as a set of XRIs > will be possible (other than allowing literals as subjects) - on the > other hand, I've starting investigating SPARQ, well, they have special > symbols which operates on literals, e.g. > > > "cat"@en //the literal "cat" has a counterpart > in the English language which points to a real world > entity (an animal) > "42"^^xsd:integer //the literal "42" is a integer > number! > "abc"^^dt:specialDatatype //"abc" is a special > datatype > > > so it seems that their use of "literals" is a bit more > evolved that simply storing a value. > Hope this could help a bit! > Giovanni > > At 10.02 19/05/2008, Markus Sabadello wrote: > > > These are two different topics: > > 1) Addressing - This is quite clear. > Everything in the XDI graph has an XRI address. Since a predicate can > not have more than one literal, it is sufficient to have the subject > and predicate in the XRI address, e.g. =markus/+email. > > 2) Storing the whole graph data (including > literals) as a set of XRIs - Bill says this is possible. And this is > what my question (and I think Nat's too) was about. > > Markus > > > On Sun, May 18, 2008 at 10:50 PM, Drummond > Reed <mailto:drummond.reed@cordance.net> wrote: > > > > Markus, > > > > > > This > subject has indeed come up several times before. I know Bill has > suggested that, when looked at from an RDF graph standpoint, every XDI > document can be represented as the set of RDF statements that appear > in the document. This would include all those whose object is a literal. > > > > > > > However when we refer to "the set of XRIs" represented by an XDI RDF > document, I have proposed that if the object of an XDI RDF statement > is a literal, the literal is NOT part of the XRI. In other words, if > you have the XDI RDF statement$B!D(B > > > > > > =markus > > +email > > > "mailto:markus.sabadello@gmail.com" > > > > > > > $B!D(Bthe XRI that identifies the literal object of > this statement (using direct concatenation syntax) is: > > > > > > =markus/+email > > > > > > That's as far as we've gone discussing it. > > > > > > Is there any reason that rule will not work? > > > > > > =Drummond > > > > > ________________________________ > > > From: Markus Sabadello [mailto:markus.sabadello@gmail.com] > > Sent: Friday, May 16, 2008 6:12 PM > > > To: Bill Barnhill > > Cc: Nat Sakimura; tatsuki@nri.com; xdi@lists.oasis-open.org > > Subject: [xdi] XDI graph as XRIs > > > > > > Hey Bill, > > > > I'm sitting together with Nat and Tatsuki, talking > about various XDI topics. One issue that came up was the following: I > think it was you who suggested a few times that every XDI document can > be expressed as a simple list of XRIs, right? > > > For example, if I have this XDI graph: > > > =markus > > +friend > > =bill.barnhill > > =drummond > > > I could just express it using these XRIs: > > > =markus/+friend/=bill.barnhill > > =markus/+friend/=drummond > > > Right? > > > Now the question is, how does that work with literals? > If I have this: > > > =markus > > +email > > "mailto:markus.sabadello@gmail.com" > > > Then what's the XRI that represents this statement? I'm sure > someone has thought about that before, but I don't really remember how > it works or if it works at all? > > > Markus > > > > > > > -- Nat Sakimura (=nat) Nomura Research Institute, Ltd. XDI.ORG Vice Chair
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