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   Re: About URI,URN,URL and FPIs

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  • From: John Cowan <cowan@locke.ccil.org>
  • To: XML Dev <xml-dev@ic.ac.uk>
  • Date: Thu, 22 Oct 1998 13:58:24 -0400

Amit Rekhi wrote:

> * Where would the [FPI resolution] service reside(client/server)?

Probably some of each, like the DNS, but maybe not.  My SocatResolver
has nothing on the server except the actual catalog files, so it
can use HTTP or FTP or whatever to fetch them by URL (= system id).

> * Would the server simply serve all the docs that contain FPIs to the client
> or would it resolve the FPIs to system IDs before serving the docs to the
> client or would it "selectively" serve files depending upon the FPIs it can
> resolve?

Who can tell?  I think providing FPI to URL mapping is the important
thing, and the others are essentially optimization hacks.

> * Could a URN also label a resource which may not necessarily be residing on
> the web?
> ( I could label a resource with a URN ,and the resource could very well be a
> set of paper documents!

Just so.  Although it isn't official, *everybody* thinks that ISBNs
and ISSNs are a paradigm case of URNs.

> DOUBT 3 :- Talking in terms of URI, if a URI is not a URLthen it HAS to be a
> URN and vice versa. Am I right?

Almost.  Theoretically there is something called an URC, which is
a piece of metadata about a resource.  But nobody has ever seen one.
In practice <!ENTITY URI "URN or URL"> works fine.

> DOUBT 4:- In HTML, I am allowed to include <!DOCTYPE HTML SYSTEM "......The
> HTML FPI .......">.

For "SYSTEM" read "PUBLIC".

> * How should browsers parse the HTML FPI, do they leave it untouched?

Usually they ignore it.  Non-browser tools sometimes check it for
one of a number of known values such as "-//IETF//HTML 2.0" or
"-//W3C//HTML 3.2" or "-//W3C//HTML 4.0".

> * If the above is true then  each HTML browser will store a local copy of
> the HTML DTD which it will use to validate the HTML instance against. Is
> this correct?

AFAIK no existing browser validates any document.  They have hard-wired
knowledge of some variant of the HTML DTD, not necessarily or typically
a standard one.

John Cowan	http://www.ccil.org/~cowan		cowan@ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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