xml-dev - Re: System identifiers and base URIs

[Norman Walsh <ndw@nwalsh.com>]

/ Jay Sachs <jay@avacet.com> was heard to say:
[...]
| An
| EntityResolver can (and probably should be required to) set the systemId
| of the returned InputSource. If the systemId is the same as the URI
| being "resolved", there is no redirection. If this is different, a
| redirection has occurred.

I certainly agree that an entity resolver can return any resource it
wants, and that the entity resolver is free to choose to inform the
application that the system identifier is anything it wants. (I'll
even argue that it should be allowed to return null if it wants, that
case is carefully spelled out in RFC2396.)

The case that I am specifically seeking community agreement on is the
second: if the URI returned in the systemIdentifier property of the
InputSource returned by the entityResolver is not the same sas the
systemIdentifier that was passed in, "redirection" has occurred (in
the RFC2396 sense) and subsequent relative URIs are relative to that
location.

| > > To make things concrete, suppose I have a document with a DOCTYPE
| > > declaration that references http://foo.bar/baz.dtd (and I'm doing a
| > > validating parse). The parser attempts to open http://foo.bar/baz.dtd,
| > > and the entity resolver opens and returns http://moo.goo/boo.dtd
| > > instead.

[I forgot to explicitly say that it also sets the systemId of the
InputSource it returns to http://moo.goo/boo.dtd]

| > > Subsequently, the parser encounters a relative URI "somefile.ent" in
| > > the DTD. It must calculate an absolute URI in order to open it.
| > >
| > > Is the resulting absolute URI "http://foo.bar/somefile.ent" or
| > > "http://moo.goo/somefile.ent"? Or is there not a definitive answer?
| > 
| > I'd say that it resolves to "http://foo.bar/somefile.net". It's up to
| > the EntityResolver to do the same redirection-like behavior if that's
| > what's it is intended to do.

I gather, Jay, that you've reconsidered and now believe that it should
be http://moo.goo/somefile.ent. Is that right?

                                        Be seeing you,
                                          norm

-- 
Norman.Walsh@East.Sun.COM | Exuberance is beauty.--Blake
XML Technology Center     | 
Sun Microsystems, Inc.    |