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The range of the HTTP dereference function

From: Tim Berners-Lee <timbl@w3.org>
Date: Tue, 19 Mar 2002 09:50:36 -0500
Message-ID: <027801c1cf55$6e02c690$84001d12@w3.org>
To: <danc@w3.org>
Cc: "'www-tag'" <www-tag@w3.org>
Dan,

Here is my argument the HTTP URIs (without "#") should be understood as
referring to documents, not cars.

URIs can identify anything.

However, different schemes have different properties.
HTTP is a protocol which provides, for the client, a mapping
(the http URI dereference function)
from URI starting with "http:" and not containing a "#" to
a representation of a document.  The document is the
abstract thing and the representation is bits.

You say that what I call document could be widened to include
cars.

Of course, you can always take a system and remove a domain
or range restriction in theory.  But if inference systems use it
and you take it away, they break.

- This is not what people do at the moment.

- The properties of HTTP are useful to know, and to be able
 to infer things from.  For example, if I ask
 { <telnet://telnet.example.org> log:contents ?x } -> { ?x a :Interesting }.
then software would be allowed to infer, from the fact that a telnet URI is
involved
that there will be no defined contents.

Similarly, if    tn:logOfPort  related a session log to the port of the
server for that session,
{ ?x tn:logOfPort   <http://www.w3.org/foo> } will be known not to match,
without retrieving <http://www.w3.org/foo>,  because it knows that logOfPort
takes as object
something which is in a class disjoint with the range of http.

These are useful rules.  They connect with common sense understandings
and also by being architectural invariants,  they provide stable bases for
building
more efficient systems.

Why do you want to extend the range of http URI dereference to cars?

plate://us/ma/123yui  could still be defined to identify cars - I don't
object to other URI schemes identifying cars.  uuid schemes can
as far as I know now.

http2://www.w3.org/foo could be defined to have return codes
"Here is the contents of x which is a document" and "Here is some
information about x"
so that as a superset of HTTP it could provide a space in which
abstract objects existed.

But http1.1 does not have that and that fact is a useful one to record, I
think

In this way, Resource in URI and Resource in RDF can be similarly anything,
but we have an important concept of a <part of the Web information space>
<document?> or whatever.
Tim
Received on Tuesday, 19 March 2002 09:50:37 GMT

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