Re: John Sowa's post on URIs etc. (01)
"This discussion raises some serious issues: (01) (02)
4. The URLs and URIs of the WWW are based on a naming
scheme that ultimately resolves to physical devices.
It guarantees that an identifier will determine a
unique storage location at a given point in time. (05)" (03)
This is not exactly true. In w3 specs [1] we read: (04)
"A Uniform Resource Identifier (URI) is a compact sequence of characters
that identifies an abstract or physical resource", and further that "in
many cases, URIs are used to denote resources without any intention that
they be accessed" and "a common misunderstanding of URIs is that they
are only used to refer to accessible resources. The URI itself only
provides identification; access to the resource is neither guaranteed
nor implied by the presence of a URI." (05)
A URL is a URI with a specialized syntax: "A URI can be further
classified as a locator, a name, or both. The term "Uniform Resource
Locator" (URL) refers to the subset of URIs that, in addition to
identifying a resource, provide a means of locating the resource by
describing its primary access mechanism". Ultimate resolution to
physical devices is *not* a part of the scheme. (06)
"
5. However, the policies of the WWW and of each domain
on the WWW permit the same identifiers to be resolved
to different physical locations at different times. (06)
" (07)
Precisely. URLs, those that do identify locations, identify them in
virtue of there being a mapping from a particular URI to a physical
address, by means of dns services. And if there is no such mapping,
there is no translation, and in effect the URL does not identify a
location -- try, e.g., 'http://www.nonsense.no', a (syntactically)
*valid* URL. Some (most?) valid URLs do *not* ultimately resolve to a
physical device. (08)
Wacek (09)
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