xmlm and names(paces)

[oleg@okmij.org]

Buenzli Daniel wrote:
> As I previously said on this list I'm adding better namespace support to
> xmlm. Up to now xmlm just parsed qualified names into their prefix and
> local part (prefix, local). Now I'd like to provide the client with
> expanded names (uri, local).
>
> Initially I planned to give the client choice between getting qualified
> names or expanded names. However the prefix of qualified names is really
> meaningless (it can be alpha converted) and thus cannot be used to
> recognize anything in a document. One of the aim of xmlm is simplicity,
> as such I think xmlm should only provide expanded names.

It should be mentioned that the prefixes of qualified names cannot
just be alpha-converted. It is quite common to see the following,
quoted from http://www.w3.org/TR/xmlschema-0/

	<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
         ...
	  <xsd:element name="comment" type="xsd:string"/>

One can plainly see that the prefix, xsd, appears inside a quoted
string! If one wishes to rename the prefix xsd into just 's', one has
to look inside quoted strings (of course, not every occurrence of xsd
inside quoted string is the prefix. A quoted string, the content of an
attribute, may just as well be an opaque quoted string).

One may really wonder what kind of people wrote all those voluminous
XML recommendations. 

So, ideally one may wish to keep the original prefix (in addition to
its corresponding URL). It is also reasonable for a user to specify a
`shortcut'. Unlike the prefix, which is chosen by the author of the
document, a shortcut is chosen by the person who invokes a parser. In
the SSAX parser, the user specifies the association of URI with
shortcuts. The parser, having resolved the QName prefix to a URI, maps
that URI to the user-specified shortcut, if present. The shortcuts are
extensively discussed in
	http://okmij.org/ftp/Scheme/SXML.html#Namespaces

Incidentally, some of the design decisions of SSAX (despite being
produced by an enemy) might be pertinent to this discussion. SSAX is
actually a SAX parser, or a big macro that builds a parser out of
user-provided callbacks and reasonable defaults. One can use SSAX to
parse XML on the fly or to convert XML to anything one chooses. There
is also an instantiation of SSAX with reasonable callbacks that make
SSAX a DOM parser, converting XML into one particular output format,
SXML. Experience shows that this particular instantiation satisfies
most of the users. Still I have come across several users who needed
the full SSAX (e.g., for streaming conversion of XML into something
else).