xdi message
[Date Prev]
| [Thread Prev]
| [Thread Next]
| [Date Next]
--
[Date Index]
| [Thread Index]
| [List Home]
Subject: Re: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
- From: Giovanni Bartolomeo <giovanni.bartolomeo@uniroma2.it>
- To: "Markus Sabadello" <markus.sabadello@xdi.org>, "Kermit Snelson" <ksnelson@subjectivity.com>
- Date: Thu, 20 Mar 2008 13:31:41 +0100
I obviously agree with this solution!
It works because we're talking about the "concept of number"
(which I prefer to have formalized as a $word. :-)
On the other hand, the problem is not totally solved: if the literal were
a string, this would not work.
Giovanni
At 12.09 20/03/2008, Markus Sabadello wrote:
My quick&simple solution to
this whole thread would be to say that literals have no semantic meaning
within XDI itself. They are just data for the consuming
application.
So if you really want to say something about the number 24, then you use
an XRI, e.g. $24, or $type$xsd$int!24, or whatever.
$24
$is
+(
http://example.com/number/of/beers/in/a/case)
Markus
On Thu, Mar 20, 2008 at 3:51 AM, Kermit Snelson
<
ksnelson@subjectivity.com> wrote:
- These issues are indeed very difficult to discuss over email, so
I'm
- all for deferring them to tomorrow's telecon.
- But in the meantime, I do have an easy-to-express-over-email thought
about this:
- > Also, the reflexive properties of "is" would seem to
hold across any combination
- > of the subjects and objects of these statements
- I'm not yet convinced that does work, actually, even in English.
The
- reasoning here:
- The number of beers in a case is 24.
- 24 is the number of hours in a day.
- Therefore, the number of beers in a case is the number of hours
in a day.
- is really no better than this:
- Sushi is better than nothing.
- Nothing is better than sex.
- Therefore, sushi is better than sex.
- The problem with the first syllogism (and it's probably already
- obvious that "nothing" is wrong with the second one) is
its
- implication that changing the number of beers in a standard case to
be
- 16 would also require changing the number of hours in a day to be
16,
- which probably isn't true.
- My point here is that using literals both as subjects and as
objects
- can cause problems even in English, and I suspect that's one of
the
- reasons why RDF, which is designed to express semantics with
- sufficient precision that even machines can't get confused,
allows
- only objects to be literals. And if only objects may be literals,
then
- it's impossible to have reflexive predicates, because
otherwise
- <
http://example.com/number/of/beers/in/a/case> <$is>
<"24">.
- would imply
- <"24"> <$is>
<
http://example.com/number/of/beers/in/a/case>.
- =Kermit
- On 3/19/08, Drummond Reed
<
drummond.reed@cordance.net> wrote:
- > To me, this is a wonderful example (or painful example,
depending on your view) of how some aspects of this subject are going to
be difficult to discuss via such a low-bandwidth medium (or at least a
slow-bandwidth medium) as email.
- >
- > To be specific, I think I understand the point Giovanni is
making, and the one Kermit is making. However, I think that if we are
very precise (which we're going to have to be in XDI RDF), they actually
illustrated why $is is reflexive.
- >
- > I'll try to quickly explain what I mean while providing
the caveat that this may be going to be hard to discuss in email, and
thus I suggest we take it up further on tomorrow's telecon (to which I'll
add it to the agenda, coming out next).
- >
- > I'm going to assume that Kermit's example of using the
predicate
"http://english.com/is" is
a clever way of saying, "the predicate known in English language as
the word 'is'". (If I was wrong about that, Kermit, let me
know).
- >
- > If so, then in "English pseudo-X3", you could
say what Kermit was expressing as:
- >
- > The number of
hours in a day
-
>
is
-
>
24.
- > The number of
beers in a case
-
>
is
-
>
24.
- >
- > If so, the inverse of both these statements would appear
to be valid:
- >
- > 24
-
>
is
-
>
the number of hours in a day.
- > 24
-
>
is
-
>
the number of beers in a case.
- >
- > Also, the reflexive properties of "is" would
seem to hold across any combination of the subjects and objects of these
statements, i.e., you could say:
- >
- > 24
-
>
is
-
>
24
- > The number of
hours in a day
-
>
is
-
>
the number of beers in a case.
- > The number of
beers in a case
-
>
is
-
>
the number of hours in a day.
- >
- > So if we agree that in all these statements the subject is
a number and the object is a number -- just described in different ways
-- then I think everything works. BUT if Kermit's point was that the
literal "24" as a subject cannot be intrinsically determined to
be a number, then I agree that there may be issues about making
statements about a literal as a subject.
- >
- > Given that, here's a challenge. What about the following
set of XDI statements (moving to formal X3 Whitespace for clarity):
- >
- >
["24"
-
>
[$is$a
-
>
[$literal]
-
>
[$type$xsd$string]
-
>
[$type$xsd$integer]
-
>
]
- > ]
- >
- > Doesn't all that make sense? (Again, I'm not necessarily
advocating for XDI subjects to allow literals. I'm just challenging the
notion that there's anything logically wrong with it. The above all
appears pretty intuitive to me.)
- >
- >
- > =Drummond
- >
- >
- > > -----Original Message-----
- > > From:
kermit.snelson@gmail.com
[
mailto:kermit.snelson@gmail.com] On Behalf
- > > Of Kermit Snelson
- > > Sent: Wednesday, March 19, 2008 12:57 PM
- > > To: Giovanni Bartolomeo
- >
- > > Cc: Drummond Reed; Markus Sabadello;
barnhill_william@bah.com
;
- > >
xdi@lists.oasis-open.org
- >
- > > 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!1
- > > 234]]
- > > > > > 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