Re: URIs quack like a duck

Clark C. Evans scripsit:

> 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).

In that case there are no serious naming systems except in extremely
closed worlds.  I can hardly think of any physical object in the Real World
that has only one name.

>  a) one de-references the function (if possible)
>     and compares the resources directly.

*sigh*
As I have repeatedly shown on this list, resources
*cannot* be compared directly, only the entity bodies that happen
to represent them at a particular moment.

>  b) an injective identification function is named.

What about direct assertions?  We can't in practice dereference the
names "Hesperus" and "Phosphorus" to determine if they identify
the same thing (because the planet Venus is not a network-retrievable
resource), nor can we, in the Real World, limit ourselves to just
one of these names.

But we can look in a database that informs us that Hesperus is Phosphorus,
an *a posteriori* truth (it is neither trivial to claim it, nor absurd
to doubt it).

So I add to your list:

   c) metadata informs us that the two URIs name the same resource.

-- 
John Cowan                                   cowan@ccil.org
	Yes, I know the message date is bogus.  I can't help it.
		--me, on far too many occasions

Received on Sunday, 4 June 2000 15:25:05 UTC