RE: Issue 7 - processing model for SOAP headers

Tim Ewald writes:

> Depends where/how you got the URI. If it was
> embedded in anchor tag in an (X)HTML page it's a
> link that can be dereferenced. If it appears in a
> namespace declaration, it is an opaque identifier
> of a namespace that may or may not be
> dereferencable. My point is, there is always some
> context, unless someone builds a service that
> simply returns a URI with no other information,
> which is likely to be useless.

Tim: I think this misses a Web Architecture disctinction that seems 
important.  In particular,

You say:  whether an identifier is dereferencable depends on where or how 
the name is used.

What I think you mean:  the appearance of a URI in certain contexts 
suggests that certain sorts of container processing are unlikely to 
succeed if the URI won't dereference.  In that sense and in that sense 
only, an expectation is created.

It's a very important distinction, I think.  A key characteristic of the 
web is that the interactions that you may attempt with a resource are at 
worst bounded by the scheme appearing in the URI, and sometimes not even 
by that (e.g. you can use the HTTP protocol to try and get a cached copy 
of a resource named with the ftp: scheme name, because the HTTP protocol 
spec says you can). 

More importantly, the retrievability of a resource can't be changed even 
by implication when I write the URI down somewhere.  I can take a 
namespace name and write:

        <a href="namespaceURI#someFrag">a link</a>

in my HTML document.   That says something >about the HTML document<, but 
nothing about the resource at namespaceURI in my opinion.  In particular, 
it suggests that rendering of the HTML is unlikely to be successful if the 
URI doesn't resolve. 

As to whether the URI will resolve, that will depend on the state of the 
resource, and perhaps other factors such as the health of the network;  it 
will not in general depend on whether the name is used in a link, as a 
namespace, etc.  I suspect this is what you meant, but the distinction is 
very important in ensuring that all web resources are in principle first 
class, and that the characteristics of a given resource can change over 
time.

Thanks!

Noah

--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
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Received on Tuesday, 25 January 2005 15:17:32 UTC