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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.


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


be the same as this?

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?
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?


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'.



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 $xsd.int*$"24" or $"24"/$isa/$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
"abc"^^dt:specialDatatype //"abc" is a special

so it seems that their use of "literals" is a bit more evolved that simply storing a value.
Hope this could help a bit!

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.


On Sun, May 18, 2008 at 10:50 PM, Drummond Reed <mailto:drummond.reed@cordance.net> wrote:


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



$B!D(Bthe XRI that identifies the literal object of this statement (using direct concatenation syntax) is:


That's as far as we've gone discussing it.

Is there any reason that rule will not work?


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:


I could just express it using these XRIs:



Now the question is, how does that work with literals? If I have this:

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?


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