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   Re: System identifiers and base URIs

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  • From: Norman Walsh <ndw@nwalsh.com>
  • To: xml-dev@xml.org
  • Date: Mon, 07 Aug 2000 10:41:03 -0400

/ Jay Sachs <jay@avacet.com> was heard to say:
| Norman Walsh wrote:
| > / 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.)
| To be explicit here: a "null" systemId on the returned InputSource would
| mean that 5.1.2 applies, and the URI is that of the enclosing context?
| Or that no redirection had occurred? Or do you mean that section 5.1.4
| applies and it's now up to the application? I suspect the first (section
| 5.1.2) is more conforming to the RFC.

I hadn't really considered that case very carefully. I'd be happy with
either an interpretation based on 5.1.2 (which would effectively make
the included entity "transparent" from a URI-perspective) or 5.1.4
which would leave it undefined. But I don't think the 5.1.2
interpretation would allow an entity resolver to return null when it
was parsing an XML DTD without violating the spirit of the XML 1.0 REC
as I understand it. (Since nested entities are supposed to be resolved
relative to the entitities that contain them.)

| > 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.
| I'd concur that the best (only?) way to define "redirection" when
| dealing with EntityResolvers and InputSources is in the difference
| between systemIds.

And we agree that this *is* redirection *in the RFC2396 sense*. Yes?

| > I gather, Jay, that you've reconsidered and now believe that it should
| > be http://moo.goo/somefile.ent. Is that right?
| Given that the systemId was changed, yes: a redirection has occurred,
| and the resulting URI is now http://moo.goo/somefile.net.

Good! :-)

Is there anyone reading this thread who disagrees?

                                        Be seeing you,

Norman.Walsh@East.Sun.COM | It is a general error to imagine the
XML Technology Center     | loudest complainers for the public to be
Sun Microsystems, Inc.    | the most anxious for its welfare.--Edmund
                          | Burke, 1769


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