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Subject: Re: [xdi] XDI graph as XRIs
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; [email protected]
> 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; [email protected]
>
> 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; [email protected]
>
> 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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