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Re: [ontolog-forum] OWL and lack of identifiers

To: "John F. Sowa" <sowa@xxxxxxxxxxx>
Cc: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Sun, 15 Apr 2007 19:34:41 -0500
Message-id: <p06230904c24872c72f36@[]>
>  > Yes, but would you agree that there is no one
>  > universal space-time coordinate system such that
>  > any physical object could have two or more unique
>  > identifiers in different coordinate systems?
>There is no problem with having multiple naming systems
>if there is a one-to-one mapping between them.
>For example, there's a one-to-one mapping between
>rectangular coordinates (x,y,z) and polar coordinates
>with a radial distance r and two angles (assuming, of
>course, that you treat angles modulo 360 degrees as
>identical).  For some applications, one coordinate
>system might be better than the other, but you can
>always transform one system to the other.    (01)

Provided you know what system they are written 
in. But to do that means you need a universally 
agreed way to refer to the coordinate system.    (02)

>But there are many issues about systems for which
>there is no unique mapping and for which there is
>no clear idea of what exactly is being identified.
>For example, a URI that points to a location uniquely
>identifies that location.    (03)

Well, that is often true, but that is not the 
intention. In fact using file names as URIs is 
explicitly deprecated by the W3C. This is why the 
W3C changed the terminology from URL (Locator) to 
URI (Identifier). See 
http://www.w3.org/DesignIssues/NameMyth.html  for 
one attempt to explain this.    (04)

>  But what happens with the
>following cases:
>   1. The contents at that location change over time.    (05)

A 'resource' in the REST model is a function from 
times to representations, rather than a single 
fixed 'contents'. For example, a URI might 
identify a real-time clock.    (06)

>   2. The contents move to another location.
>   3. The contents are identical to the contents at
>      many other locations.
>   4. The contents can be interpreted in many different
>      ways -- e.g., does the URI identify a web page or
>      the service supported at that web site?
>Similar problems occur with most other naming systems,
>but they become especially difficult when you're talking
>about abstract stuff like information.    (07)

True, they do get rather tricky. But to give the 
W3C some credit, they are aware of these issues 
and are trying very hard to get them sorted out 
and clarified. See the archives of the Web 
architecture (TAG) working group, to get a sense 
of how hard this is.    (08)

Pat    (09)

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