Re: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-02-26

[Nick Nicholas <opoudjis@optushome.com.au>]

I will do an overview answer to this series of posts later on today I  
hope. It's unfair of me to zoom in on this post, because it's a  
digression to what Giovanni was saying (and I haven't grasped the  
point he was making yet); but:

Predicates in XDI have denotations: +friend as a class is the class of  
all objects of the predicate +friend.

*But* that does not do away with reification: predications can still  
be reified, and denote states of affairs, rather than objects of  
predicates.

So:

+friend is the class that includes {=Drummond}, because Drummond is a  
friend to someone.

=Bill/+friend/=Drummond also has a denotation --- =Bill (if I'm not  
mistaken).

But that does *not* mean you can plug =Bill anywhere you see =Bill/ 
+friend/=Drummond . In particular:

=John/+says/(=Bill/+friend/=Drummond) does not mean the same as =John/ 
+says/=Bill


Now, +friend is a predicate, and is inherently relational. But when  
used as an RDF subject or object (a term), it denotes individuals, not  
states of affairs. And it cannot be used in place of a state of affairs:

(=Bill/+friend/=Drummond)/$is$a/+true-statement     makes sense
=Bill/$is$a/+true-statement                         does not
+friend/$is$a/+true-statement                       does not either

because when it is a term, +friend is not anything different to =Bill:  
it is a class of individuals, and /$is$a/+true-statement only applies  
to states of affairs (reified predications). Similarly,

(=Bill/+friend/=Drummond)/+since/2006               makes sense
=Bill/+since/2006                                   does not
+friend/+since/2006                                 does not either

for the same reason.

Hope that makes sense...

On 06/03/2009, at 02:06, Giovanni Bartolomeo wrote:

> G: I think that the "instance" you are referring here is not  
> =Drummond, instance of the individual class ("="), but =Bill.Barnhill 
> +Friend=Drummond, an instance of =Bill.Barnhill+Friend class (which  
> could be in turn an instance of +Friend). Consider this example:
>
> +Friend/$has/+since
>
> =Bill.Barnhill+Friend=Drummond/+since/"02-10-1998" (i.e. the  
> individual =Drummond, casted to +Friend, in the context of  
> =Bill.Barnhill, has the property +since - which is obviously context- 
> dependent, i.e. changes with the context, =Bill.Barnhill 
> +Friend=Giovanni/+since/"05-03-2007")
>
> But would =Drummond/+since/"02-10-1998" or =Drummond/ 
> +since/"05-03-2007" make any sense?
>
> Another way to say this is that =Drummond would exist even without  
> being a friend of mine, or a friend of anyone. It exists because it  
> is an instance of the individual class ("=").
>
> The issue is whether =Bill.Barnhill+Friend=Drummond and =Drummond  
> should point to the same XDI resource, e.g. whether =Bill.Barnhill 
> +Friend=Drummond/$is/=Drummond or =Bill.Barnhill+Friend=Drummond/$is 
> $a/=Drummond (as the implication suggested by Drummond +x/$has/+y -- 
> > +x+y/$is$a/+y would suggest). Probably we need to elaborate a bit  
> more on this.

--
  Dr Nick Nicholas: Link Affiliates    opoudjis@optushome.com.au
http://www.opoudjis.net                          skype:opoudjis
   "Must I, then, be the only one to be beheaded now?" "Why, did you  
want
everybody to be beheaded for your consolation?" Epictetus, Discourses  
1.1.