[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Are people really using Identity constraints specifie
Rick, And this is the crux of the problem here as you describe it: <snip> XML Schemas is admittedly not powerful enough to express contingent constraints well--they are often dynamic--, but it is rather inconvenient for expressing static necessary constraints. In part this is because of content models: you really have to fight with grammars to make them open and extensible. In particular, many people are aware that enhancing a derived schema often involves rejigging the base schema. It is because XML Schemas started from the wrong position: "lets have base schemas and be able to derive schemas from them" rather than "lets have necessary schemas and be able to declare extra contingent constraints", which would have made "open" content models the default, for example. (This is an issue Roger championed, unfortunately too late!) Quoting rjelliffe@a...: </snip> Both Schematron and CAM take the opposite approach and allow the baseline structure and extra varients to be declared dynamically. I feel at times like the W3C Schema TC is continuing to attempt to squeeze the last few ounces out of their 'paddlewheel sternwheeler' design - while we now have screw propellers available... DW.
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