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All this talk of PSVI leads me to ask one question. Who has actually
implemented the PSVI? Sorry, my mistake. I should astart with, who has
implemented the XML infoset?
PITHY WORDS OF WISDOM
You know you hypochondria is really bad when you learn to read your
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You assume all risk for your use. (c) 2002 Microsoft Corporation. All
> -----Original Message-----
> From: Simon St.Laurent [mailto:email@example.com]
> Sent: Thursday, May 09, 2002 8:15 AM
> To: firstname.lastname@example.org
> Subject: [xml-dev] PSVI formalization
> Recent discussions here about XQuery, XPath 2.0, and their
> knotted relationships with W3C XML Schema have made me think
> a fair amount about the relationship between XML and W3C XML
> Schema, particularly the Post-Schema Validation Infoset
> (PSVI), more deeply.
> There were a bunch of presentations last year about how XML +
> XSD -> XML 2.0, something I found merely annoying then but
> which makes more sense now. The community that craves these
> features is poorly served in many ways by XML 1.0, with its
> text orientation, structures that can be loose to the edge of
> complete unpredictability, and a human-readability
> requirement that is incredibly verbose but useful in many
> cases only for debugging stages.
> XML 1.0 is now more and more buried under layers of other
> processing, and the common foundation for W3C work moving
> forward appears to be the PSVI - or at least an enormous
> amount of effort is going into integrating the PSVI with a
> large number of projects, and it seems that most of the
> vendor and programmer excitement these days is focused on the
> PSVI, not the brutish markup that lurks underneath.
> The PSVI seems to be what programmers and database folks
> want. It offers strongly typed and highly structured
> information, already guaranteed to conform to their
> expectations. It has the same flexible named hierarchies
> that XML offers, with none of the messy concerns about
> character encodings, CDATA sections, or the limitations of
> text for storing binary information.
> At the same time, the PSVI is pretty difficult to express in XML.
> Layers of type information can make it complex to pin down
> how best to describe a particular piece of information.
> Object-oriented development manages that every day, but
> doesn't have to express the whole hierarchy for every piece
> of information in a flat representation. Given recent
> discussions of synthetic PSVIs, it's not always clear that
> I'm concluding from all of that that XML is not a good
> foundation for the kinds of information developers want from
> the PSVI, and that retrofitting XML to carry that information
> is perhaps the root cause of the complexity explosion we're
> seeing in W3C XML Schema and specifications which build on
> it. It seems to me that it might be wiser to use the PSVI
> directly for more abstract information modeling rather than
> expecting XML representations to carry the load.
> So where does this take us? Developers who want to work with
> the PSVI should work with the PSVI, and not worry about XML.
> The kind of interoperability the PSVI is designed to provide
> is very different from the kind of interoperability that XML
> provides - a perfectly reasonable conclusion given the
> different situations leading to the creation of their
> respective specifications.
> Beyond that, it seems like some easily-exchanged
> representation of the PSVI is in order. XML works, sort of,
> but it seems pretty obvious that there are better approaches
> to representing information if you have all the information
> the PSVI provides rather than a simple "all is text"
> approach. This could easily be a binary format, though text
> might also be an option.
> XML has done a wonderful job of convincing the world that it
> is possible to agree on base formats for some kinds of
> information, and that generic tools (parsers, editors, etc.)
> can be useful for a wide variety of specific problems. It
> seems reasonable to suggest that the lesson of XML is not
> "everyone must use angle brackets and text" but rather that
> "shared information formats are really useful when supported
> by a reasonable set of tools".
> Given the immense bias in current XML work at the W3C toward
> support for the PSVI, it seems like it might well be time to
> find an appropriate means of expression for the PSVI.
> Conversions from strongly typed PSVI to loosely typed XML
> should be trivial, while XML to PSVI should only require a
> W3C XML Schema (or other PSVI generator) to provide the
> necessary information.
> PSVI processors could use or extend existing XML
> infrastructures, replacing only the bottom layer - the parser
> - and possibly developing its own structures for the layers
> above. I suspect that taking the PSVI to its fullest
> potential is going to involve a lot more work than taking
> untyped markup to its fullest potential. It's simply a
> larger set of problems.
> A binary PSVI format could sure make XML-RPC (PSVI-RPC?)
> messages a lot smaller. All it takes is a spec, some free
> parsers, and some tools.
> Maybe someday programmers will look back on XML as the
> bootstrap phase of the PSVI, while the occasional markup geek
> still pokes around CDATA sections.
> Simon St.Laurent
> Ring around the content, a pocket full of brackets
> Errors, errors, all fall down!
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