OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.

 


Help: OASIS Mailing Lists Help | MarkMail Help

xdi message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]


Subject: XDI expressivity (was RE: [xdi] Re: $greater, $lesser, etc.)


Giovanni,

 

I apologize for not responding on this thread earlier but I have been in a solid week of meetings in Boston as well as prepping for RSA all next week so I am behind on my email. It will be another ten days before I’m able to start getting caught up.

 

However since I’m on a plane back to Seattle right now, and since you’ve asked such an _excellent_ question that raises a subject I’ve been eager to start discussing, see my answer below your message.

 


From: Giovanni Bartolomeo [mailto:giovanni.bartolomeo@uniroma2.it]
Sent: Friday, April 04, 2008 3:39 AM
To: xdi@lists.oasis-open.org
Subject: Re: [xdi] Re: $greater, $lesser, etc.

 

Dear All,

I've just elaborated a bit more on my previous comments.. BTW I didn't receive any answer, maybe I'm missing something, but I think this is a relevant point:

At 18.51 31/03/2008, Giovanni Bartolomeo wrote:

What it is still a bit obscure to me are the following statements:

=giovanni/+phone+home/"+39 06 4451843"

=giovanni+phone/+home/"+39 06 4451843"

aren't they equivalent? furthermore, aren't they both asserting the 
same as giovanni+phone+home/$type$xsd$string/"+39 06 4451843"?

Giovanni


What I realized is that these three statements:
a. =giovanni+phone+home/$type$xsd$string/"+39 06 4451843"
b. =giovanni/+phone+home/"+39 06 4451843"
c. =giovanni+phone/+home/"+39 06 4451843"

are actually NOT equivalent in terms of semantics:
a. is asserting that the type for =giovanni+phone+home is a string and its value is "+39 06 4451843"
b. is asserting that =giovanni's phone at home is "+39 06 4451843", being =giovanni the subject
c. b. is asserting that =giovanni+phone's a property, home, which is equals "+39 06 4451843", being =giovanni+phone the subject

HOWEVER in order to enforce consistency, these three addresses
a. =giovanni+phone+home/$type$xsd$string/
b. =giovanni/+phone+home/
c. =giovanni+phone/+home/

should point to the SAME node in the XDI graph (or be aliases). Is this correct? What do you think?

Giovanni

 

********** Drummond replies **********

 

I am so glad someone finally asked this question in black and white – I have been thinking about this issue of “XDI expressivity” for months now given the fundamental capabilities of XDI RDF. Forgive me for providing an extended answer, but I think the question can be so revealing about the power of XDI RDF.

 

First, to answer your question right up front, “Do those three XDI addresses identify the same literal node?”, my answer is: “You cannot know deterministically without reference to the XDI dictionaries used by the statements.”

 

The reason is that the three statements represent three different paths through the XDI RDF graph, and as you pointed out, each path represents different semantics. So you you really have to drill all the way down into the graphs, and the statements represented by each graph, in order to answer your question.

 

To do this, let’s start by looking at the three graphs visually in X3 Simple (one reason I love X3 Simple is that it lets you see the visual pattern of the graph while at the same time seeing the addresses).

 

#1

=giovanni+phone+home

          $type$xsd$string

                      "+39 06 4451843"

#2

=giovanni

          +phone+home

                      "+39 06 4451843"

#3

=giovanni+phone

          +home

                      "+39 06 4451843"

 

Now, let’s “fully explode” each of these into ALL the XDI statements they represent.

 

#1 (5 statements)

=giovanni

          $has

                      +phone

=giovanni+phone

          $has

                      +home

$type

          $has

                      $xsd

$type$xsd

          $has

                      $string

=giovanni+phone+home

          $type$xsd$string

                      "+39 06 4451843"

 

#2 (3 statements)

=giovanni

          $has

          +phone+home

+phone

          $has

                      +home

=giovanni

          +phone+home

                      "+39 06 4451843"

 

#3 (2 statements)

=giovanni

          $has

                      +phone

=giovanni+phone

          +home

                      "+39 06 4451843"

 

Isn’t it fascinating that the first graph represents five statements, the second three, and the final one only two?

 

In any case, all three options here (plus more - see below) appear to be completely valid chains of XDI statements between the XDI subject =giovanni and the XDI literal "+39 06 4451843". But none of them asserts exactly the same semantics (the only way to do that would be to use XDI synonyms, i.e., $is statements). However using an XDI reasoner and an XDI dictionary (which itself is just a set of XDI statements comprising definitions), you could verify that according to that dictionary, all these statements identify the same literal node.

 

In fact the dictionary is pretty short. Here it is:

 

+phone

          $is$a                                        <--1-->

                      +

                      $type$xsd$string

          $has                                         <--2-->

                      +home

          $a$has                                      <--3-->

                      +home

          $has$a                                      <--4-->

                      +home

          $a$has$a                                  <--5-->

                      +home

+home

          $is$a                                        <--6-->

                      +

          $has                                         <--7-->

                      +phone

          $a$has                                      <--8-->

                      +phone

          $has$a                                      <--9-->

                      +phone

          $a$has$a                                  <--10-->

                      +phone

$type

          $has

                      $xsd

$type$xsd

          $has

                      $string

 

As short as it is, the semantics represented by those statements – while crystal clear from a pure XDI semantics point-of-view – represent a surprising range of grammatical relationships a human POV. Roughly translated to English, the first ten statements say:

 

1) A phone is both a subject (noun) and a label for a type of data (typically called a “phone number”, but often abbreviated in English as just “phone”).

 

2) A phone can have a home, i.e., as a noun, it can have a possessive relationship with another noun, home.

 

3) A phone is something a home can have (possessive relationship).

 

4) A phone has an attribute of home.

 

5) Phone is an attribute of a home.

 

6) Home is a subject.

 

7) A home can have a phone (possessive relationship – inverse of #3).

 

8) A home is something a phone can have (possessive relationship – inverse of #2).

 

9) A home has an attribute of phone (inverse of #5).

 

10) Home is an attribute of a phone (inverse of #4).

 

Armed with that dictionary, an XDI reasoner can quickly prove that all the following XDI statements identify the same literal:

 

=giovanni+phone+home/$type$xsd$string/
=giovanni+home+phone/$type$xsd$string/

=giovanni/+home+phone/

=giovanni/+phone+home/
=giovanni+phone/+home/

=giovanni+home/+phone/

 

However, if you remove any of those XDI dictionary statements, some of the above are no longer provably true. For example, if you remove the statements:

 

+phone

          $has

                      $home

+home

          $a$has

                      +phone

 

Then you could no longer prove that the following two statements identify the same XDI object as the rest:

 

=giovanni+phone+home/$type$xsd$string/
=giovanni/+phone+home/

 

They MIGHT identify the same literal as the rest, but now you have nothing you can prove that with.

 

There’s much more I’d like to say about this simple dictionary, but I’m out of time. However I encourage everyone who is interested to study it closely. To test your knowledge, here’s a quiz question:

 

          “Given the dictionary above, how can you prove that it is valid for the XDI object of all six statements to be a literal string?”

=Drummond




[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]