That appears to be the "bold new computing direction" of the month for Microsoft. I think it's a bad idea.... The $5000 Question: Should we not have native support in a programming language for XML Schema? Why all this mapping nonsense?
<flame>Schema is a design-by-committee monstrosity that makes the old Ada programming language look clean by comparison, combining the worst features of SQL and VB. Why would anyone want to bake it into a programming language?</flame>
Schema does a decent job of letting you define XML structures. It also has a fairly nasty hodgepodge of types that, while awkward, at least allow you to express the intent of what you want to see in different components of your XML. Then it adds a truly bizzare set of ways to get down to the detailed level of what each component should be - things like the multitude of facets, regular expression matching, extensions of restrictions and restrictions of extensions, etc. What makes the latter set of detailed data descriptions of little use in practice is that there's no way to condition the values permitted for one attribute or element on the values (or even presence or absence) of another attribute or element.
To quote another colleague of mine: "the W3C really created a monster with XML Schema. It's far more powerful and expressive than most OO type systems like C# or Java."
Sure, you can do really complex descriptions of simple text values in schema - there's a 100-page ISBN number schema I use as a look-at-that example in training classes, for instance - but why would you want to? For real applications schema validation is going to be prohibitively expensive once you get into the complex rules, and most applications require more intelligent data validation than schema can support anyway.
My recommendation for anyone writing schemas is to use it for structure and basic data types, but stay away from the facets and such unless you really have a need to use them for descriptive purposes... and then don't write your program on the assumption that the facets will be enforced, for two reasons: (1) if someone changes the schema your code will break, and (2) schema validation will probably be turned off when you're deployed.
- Dennis
Dennis M. Sosnoski Enterprise Java, XML, and Web Services Training and Development Support http://www.sosnoski.com Redmond, WA 425.885.7197
