Re: URIs quack like a duck

On Sun, Jun 04, 2000 at 03:17:45PM -0400, Clark C. Evans wrote:
> On Sun, 4 Jun 2000, Dan Brickley wrote:
> > Imagine someone else creates another URI scheme, also used for naming
> > individuals and/or orgs. And that some Web data uses your scheme to talk
> > about me as urn:mm-agent-namespace:034543532423432 and some other data
> > uses person:uk:nx-930366b. 
> 
> In this case, the resource is identified through
> two different and uncoordinated URI schemes.

How do you know its the same resource?

> Another related case is when a single URI scheme
> does not gaurentee uniqueness.  The http: scheme
> is one of many examples.  
> 
> Either of these cases makes the mapping from
> the URI world to the resource world non-injective.

You are assuming that you have some out of band mechanism for
knowing that two Resources are the same thing. There is no 
such mechanism allowed at that level of the web. 
Its the difference between syntactic equivalence and functional
equivalence.

> When the mapping from the URI domain to the resource
> domain is non-injective, then one cannot tell, in
> *every* case if resources identified are equivalent
> by comparing the URIs.   This is a problem for any 
> serious naming system, a function is not strong enough.  
> The function must also be *unique* (injective).

It is injective. You're are just asserting through some untrustworthy
mechanism that two Resorces are equal. As far as the Web is
concerned, the only equivalence function allowed is based
on syntactic URI comparison....

> > From an RDF perspective, this topic is proving a real implementation
> > headache. There's one of something (flesh and blood entity) and two of
> > something else (Web names for that entity, aka URI). There seems to be
> > utter confusion in the community as to whether we have one Resource (the
> > person), two Resources (one each for the two URIs), or even three.
> 
> This problem is not going to go away; and I personally
> don't believe that it is solveable unless:
> 
>  a) one de-references the function (if possible)
>     and compares the resources directly.
> 
>  b) an injective identification function is named.

B is the correct one and its already defined by the URI space...

> IMHO, since (a) is not practical, this *forces* us to 
> look for a way to make (b) work.

B already works....

> I suggest the creation of a *new* URI scheme for 
> namespaces such that:
> 
>     (a) comparisons within the scheme gaurentee uniqueness
> and (b) comparisons between schemes are not allowed

Your assertions to the contrary, all URIs have this function...

-MM

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Received on Monday, 5 June 2000 10:08:23 UTC