Namespaces and PURLs

[Dan Brickley]

On Fri, 5 Jun 1998, Tim Bray wrote:

> At 03:15 PM 6/4/98 UT, Simon St.Laurent wrote:
> >>The namespace name, to serve its intended purpose, should have the 
> >>characteristics of uniqueness and persistence.  It is not a goal that
> >>it be directly usable for retrieval of a schema (if any exists).
> >
> >This sounds like I can use a PURL 
> 
> A PURL sounds highly appropriate to me for namespace identification. -Tim

The only complication I can think of is the use of the '#' fragment
identifier in the 'src=' attribute... Not sure if it makes sense to use
'#' in this context anyway, but the following from the PURL FAQ is
probably worth bearing in mind.

Dan



>From the PURL FAQ at http://purl.oclc.org/OCLC/PURL/FAQ#toc5.7

5.7 Can I use local references in conjunction with a PURL? (i.e.,
http://purl.foo.com/ME/HOME#LREF)

There's more to this question than meets the eye. Let's break it down into
manageable pieces. 

First, the local reference (i.e. #LREF) is a directive to the HTTP client
(browser). When you
select a URL containing a local reference, only the portion of the URL
preceding the local
reference is requested from the HTTP server. It is the client's
responsibility to act on this
directive in relation to the requested document once the document is
received. Therefore this
behavior is dependent upon the client. Not all clients handle local
references the same way. 

PURLs can not contain local references because we do not allow them to
contain the "#"
character. Since browsers would not send the local reference (i.e.,
anything after and including a
"#" character, such as #LREF) part of a PURL to the PURL resolver, there'd
be no point in
allowing it. 

You can use local references appended to PURLs so that your browser
attempts to locate the local
reference within the document retrieved by the PURL, but some browsers
(incorrectly) drop the
local reference upon receiving the redirect from the PURL resolver
(actually any redirect from
any HTTP server) and therefore fail to act on the local reference
directive when the actual
document is received. 

As a result, PURLs with local references appended to them, such as
http://purl.oclc.org/OCLC/PURL/FAQ#toc6.0, resolve to (the beginning of)
the document
referenced by the PURL under some Web browsers. To determine how your
browser behaves, try
the example PURL above. If it takes you to the top of this document, then
your browser is not
handling local references correctly. If it takes you to section 6.0 of
this document, then your
browser is handling local references correctly. Either way, you should
still end up with this
document. 


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