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Re: [PRD] Proposal for object representation (and ACTION-592 complete)

From: Gary Hallmark <gary.hallmark@oracle.com>
Date: Mon, 09 Mar 2009 14:18:29 -0700
Message-ID: <49B587A5.1040306@oracle.com>
To: Christian de Sainte Marie <csma@ilog.fr>
CC: kifer@cs.sunysb.edu, RIF WG <public-rif-wg@w3.org>
A variable can represent many values.  E.g.

forall ?x if ex:a(?x) then ex:b(?x)

?x is 1 and 2.

Path expressions are just a shortcut for a variable.  E.g.

if _obj.slot > 2 and _obj.slot <= 5 then ...

is short for

forall ?z if _obj[slot->?z] and ?z > 2 and ?z <= 5 then ...

Christian de Sainte Marie wrote:
> Michael,
> Michael Kifer wrote:
>> these things are called path expressions and they are not necessarily
>> single-valued. For instance, FLORA-2 uses them alongside the frames,
>> and they are simply shortcuts for some forms of conjunctions of frames.
> I have taken the action to rework my proposal to separate the issues 
> of single-valued attributes, and path location.
> But that supposes that I understand how path locations can be 
> multi-valued: as much as I understand that, as atomic assertions, 
> frames that associate different values to the same object-attribute 
> pair can be true at the same time; as much I cannot understand how a 
> path expression, as a basic term, can represent more than one value. 
> Actually, dealing with single-valued attributes in a way that seemed 
> intrinsically appropriate for them - which frames are not - and that 
> is quite usual in object-oriented languages was the main reason for my 
> proposal.
> I mean, other basic terms, such as a constant symbol, a variable, or a 
> ground function call, represent, cannot represent but a single value: 
> how can a path expression, as a basic term, represent more than one? 
> Of course, it can be set-valued, but it still has a single value, 
> which is the set.
> Can you please clarify? An example would, also, certainly help me 
> understand better what you mean.
> Cheers,
> Christian
Received on Monday, 9 March 2009 21:19:27 UTC

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