- From: <noah_mendelsohn@us.ibm.com>
- Date: Thu, 4 Aug 2005 11:45:44 -0400
- To: "Michael Kay" <mike@saxonica.com>
- Cc: "'Pete Cordell'" <petexmldev@tech-know-ware.com>, xmlschema-dev@w3.org
Pete Cordell writes: > While I see your point, I feel that XML schema is > about 10 to 20 times more complex than an XML > parser (a rough estimate based on implementation > experience). I'm not defending the complexity of XML Schema. A number of features were put in that I thought were intended as experimental during the CR period, and we were so far behind schedule that time was never mind to trim it down (my personal opinion only.) It's more complex and thus more expensive to implement than it should be. The spec. is ultimately quite precise on most points, but takes a lot of energy and patience to learn to read (unfortunate). > Therefore, it isn't necessarily > appropriate to extrapolate what has > worked well for XML to XML schema. I'm not worried so much about the implementers as the users. XML Schema is no more complex to implement well than languages like, say, Java. Would you feel good if JavaSoft promoted a checklist so that vendors could say, I don't support: _ for loops _ interfaces _ casts _ protected etc.? There would be pandemonium. Nobody could write a Java program that would work in more than one place. Of course, in a limited community of those who are part way along in their implementations, such lists are very useful for interop testing. They are the last thing that users want to see vendors promoting in commercial products. It's not that schema is as simple as XML, it's that the goal is the same: both are used for interoperation across dynamically changing sets of organizations using whatever software those organizations use in the moment. For that to work, each schema must mean the same thing wherever its used. We have made a few (controversial) exceptions mostly having to do with latitude as to where schema documents are located, and implicitly, which ones are trusted. Otherwise, a given schema must mean the same thing in all implementations, just as the same Java program must mean the same thing in all conforming Java VMs. I think that's very important. Mike Kay writes: > I think there are a number of processors > that are very close to complete > conformance, which suggests to me that it's now reasonable to expect such nearly complete conformance, at least from implementations marketed on a large scale by major suppliers (commercial or open source) for general purpose use. No doubt, if the spec were simpler, there would be more such implementations built by smaller teams with less funding, and that would have been a very good thing. I have very little sympathy for the well funded organizations that do schema as their day jobs and who, after a number of years, are failing to provide the levels of conformance that Mike and others are showing to be practical. As Mike says, a fairly high degree of conformance is now being shown to be practical through multiple implementations in multiple organizations. It's not the W3C's business to bless or diss particular implementations, but I think it would be really good if the user community could find ways of publicizing which implementations are complete and correct and which aren't. I'm sure the W3C will be glad to help arbitrate factual questions as to what behavior is correct. I think the energy spent in that direction will be far more beneficial than energy spent providing standard documentation for the errors in broken implementations. As Mike says, the remaining issues in the more respectable implementations tend to be rather tricky (though sometimes significant) edge cases that if listed would result in a table that few novices would understand. -------------------------------------- Noah Mendelsohn IBM Corporation One Rogers Street Cambridge, MA 02142 1-617-693-4036 --------------------------------------
Received on Thursday, 4 August 2005 15:46:03 UTC