[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: PSVI formalization
Well, the issue we are discussing is not so much whether or not we need another schema language as whether we need *any* schema language. If you're talking about defining standard vocabularies or "core components" then I agree, that's a more pertinent question. Without that, none of the web services or semantic web business is going to fly. Matt > -----Original Message----- > From: Sebastian Schnitzenbaumer [mailto:schnitz@m...] > Sent: Thursday, May 09, 2002 7:39 PM > To: Matthew Gertner; Simon St.Laurent; xml-dev@l... > Subject: Re: PSVI formalization > > > Isn't the issue, instead of whether or not we need another Schema > language, how do those schema languages interact when defining > semantic modules that can be re-mapped into different bigger > markup languages, to limit the space of N^N by using atomic > language modules instead just tags and attributes as the smallest > unit of semantics? > > - Sebastian > > > -----Ursprüngliche Nachricht----- > Von: Matthew Gertner > Gesendet: Do 09.05.2002 18:35 > An: 'Simon St.Laurent'; xml-dev@l... > Cc: > Betreff: RE: PSVI formalization > > > > Simon, > > Cool, I was about to respond to your other post, but this is a > much clearer > formulation of the issue. Your initial premise is exactly right: > what gets > developers excited about XML is the prospect of schema-enabling > it. > Certainly that's true for me (your humble PSVI poster boy), and > you're also > right that I don't like CDATA, NOTATIONs and the like. > > I think where you are missing the boat is the assertion that > somehow there > could be some alternative representation of the PSVI that > wouldn't be XML > but would satisfy all the gearheads out there. Frankly this is a > crazy idea. > It took decades for something like XML to appear, and it's a > huge boon. We > are developing software right now that uses XML along with > schema (having > created our own version of the PSVI two years ago), and we also > use XML > parsers, XML editors, XPath, XSLT and a whole slew of other XML > technologies > and tools. Why on earth would we reinvent the wheel when XML > works for us!? > Just to preserve the "purity" of the language for the benefit of > some markup > Luddites? > > Someone on XML-Dev recently hit the nail on the head when they > talked about > the N^N complexity of XML integration. The only solution is to > have commonly > agreed-upon semantics for the documents, as someone else pointed > out. The > most basic semantics relating to structural and datatyping > constraints are > contained in a schema, and already make a lot of generic > processing > possible. Without this, you really can't do anything useful with > an XML > document without writing specific code, and the whole > XML-on-the-web vision > falls apart. > > I simply can't get away from the suspicion that your objection > lies more in > the specific instantiation of XML Schema, PSVI, XPath, XQuery, > etc. rather > than the underlying concepts. If you're such as schema skeptic, > why did you > waste all of that time with DDML? The idea of well-formed vs. > valid > documents has been around since the genesis of XML, and I don't > remember > anyone getting upset about it until we started being faced with > an array of > 200-page specs that no one can understand. I would submit that: > > 1) You are upset to see a 35-page spec turn into a 160-page spec > with > assorted dependencies in other huge specs (XPath), and this is > understandable. The notion of strong typing in XPath doesn't > seem so > horrible to me, but the bloat of the spec does. In other words, > the W3C is > increasingly unable to produce simple specs. > > 2) You are upset because it is harder and harder to divorce > well-formed > documents from valid documents. In other words, the W3C is > increasingly > unable to produce layered specs. > > I can't imagine an objection to the notion that XML can be > associated with a > schema, and when it is it becomes a valid document and the > behavior of > certain associated specs is extended accordingly. For example, > XPath can do > design-time type checking. If there is no schema, the document > is > well-formed and this "baggage" is ignored. > > Maybe you are being purposely provocative (I can relate, lord > knows), but > the idea that XML+schema is somehow no longer in the spirit of > XML is > absurd. > > Matt > > > -----Original Message----- > > From: Simon St.Laurent [mailto:simonstl@s...] > > Sent: Thursday, May 09, 2002 5:15 PM > > To: xml-dev@l... > > Subject: 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 > > XML+schema->PSVI. > > > > 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! > > http://simonstl.com > > > > > > > ----------------------------------------------------------------- > > The xml-dev list is sponsored by XML.org <http://www.xml.org>, > an > > initiative of OASIS <http://www.oasis-open.org> > > > > The list archives are at > http://lists.xml.org/archives/xml-dev/ > > > > To subscribe or unsubscribe from this list use the > subscription > > manager: <http://lists.xml.org/ob/adm.pl> > > > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, > an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://lists.xml.org/ob/adm.pl> > > > >
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