This is the mail archive of the
xsl-list@mulberrytech.com
mailing list .
www-tag: Potential new issue: PSVI considered harmful
- From: David Carlisle <davidc at nag dot co dot uk>
- To: xsl-list at lists dot mulberrytech dot com
- Date: Mon, 17 Jun 2002 11:12:51 +0100
- Subject: [xsl] www-tag: Potential new issue: PSVI considered harmful
- Reply-to: xsl-list at lists dot mulberrytech dot com
Anyone (Jeni:-) who thought I was "strident" in my criticism of the over
dependence of XPath2 on W3C Schema might be entertained by the thread
which starts at:
http://lists.w3.org/Archives/Public/www-tag/2002Jun/0085.html
A few highlights...
Tim Bray:
4. Work on XQuery and other things that require a Type-Augmented Infoset
must not depend on schema processing, and should not have normative
linkages to any schema language specifications.
Simon St.Laurent:
I'd say this item is a crucial requirement if the W3C wants to avoid a
serious fork in XML development. Efforts to impose the PSVI as part of the
XML core are not very welcome in a lot of places.
James Clark:
I see several different problems with the PSVI.
(a) It makes documents less self-contained.
(b) Applications that depend on a PSVI now require a very complex,
heavy-weight schema validation process, rather than a relatively simple
parsing process.
(c) Applications that depends on a PSVI must agree not only on the choice
of schema language but also on the choice of mechanism to locate the
schema. As has been pointed out, xsi:schemaLocation is just hint; there is
no single way that is mandated for an application to locate a schema. XML
Schema does not specify a single way to get from a URI specifying a
document to a PSVI; it only specifies the way to get to a PSVI from a URI
specifying a document together with a mapping from namespace URIs to schema
locations.
(d) The PSVI is not XML; this is the most insidious problem. With something
like default values, you can perform a normalization process and produce a
self-contained document where defaults are explicit. The declaration of
default values defines a mapping from an XML infoset to another instance of
an XML infoset. It is not necessary to add complexity to applications to
deal with default values. However, the W3C XML Schema PSVI is not like
this; a PSVI is not an XML infoset. You cannot perform the PSVI infoset
augmentation as a separate XML to XML transformation. All applications
dealing with the PSVI are dealing with a different, more complex structure
than applications that deal with pure XML. Applications communicating with
the PSVI become much more tightly coupled: when applications communicate
using the XML infoset, they do not have to share an address space, because
there is a standard serialization of an XML infoset as XML, but this does
not apply with the PSVI. I believe this is a catastrophic architectural
mistake in XML Schema, and it needn't have been like this: schema infoset
augmentation could and should be defined as an XML to XML transformation
process.
_____________________________________________________________________
This message has been checked for all known viruses by Star Internet
delivered through the MessageLabs Virus Scanning Service. For further
information visit http://www.star.net.uk/stats.asp or alternatively call
Star Internet for details on the Virus Scanning Service.
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list