In response to my earlier post on his "Replace & Defend" theory Jon Udell writes

We have yet to even scratch the surface of what's possible given these circumstances. And now here comes WinFS with its own proprietary schema language. In recent years, it's been popular to layer innovation on top of base standards. So XSLT, XQuery, and SQL200n all rely on XPath, as WSDL relies on XSD. Yet no base standards beyond XML itself were of use to WinFS? It puzzles me. The things defined in WinFS don't seem exotic or mysterious. "A WinFS Contact type," the docs say, "has the Item super type. Person, Group, and Organization are some of its subtypes." If XSD can't model such things, we're in real trouble.

I doubt that anyone is claiming that W3C XML Schema cannot model containment or type derivations, however the way it does implements type derivation leaves much to be desired. In fact, this is the topic of an article I wrote that showed up on last week entitled XML Schema Design Patterns: Is Complex Type Derivation Unnecessary?. This is just another example of how things that seem straightforward end up being fairly complicated in W3C XML Schema. As Don Box puts it XML Schema has already eclipsed C++ in terms of complexity. Given that the WinFS schema language isn't even about modelling XML documents it seems perplexing that one would expect it to take on the complexity of using W3C XML Schema as its modelling language.

Of course WinFS does much more than model datatypes and structures. It's a highly sophisticated storage system that supports relational, object, and XML access styles, and that treats relationships among items as first-class objects in themselves (a potent feature I first encountered in the object database world years ago.) Great stuff! But the terminology of the Longhorn docs is revealing. Person, Contact, and Organization items are referred to as "Windows types," presumably because their schemata appear as classes in Longhorn's managed API. But to me these are universal types, not Windows types. I had expected them to be defined using XML Schema, and to be able to interoperate directly with SOAP payloads and XML documents on any platform.

Being defined using W3C XML Schema and being able to interoperate directly with XML documents on any platform are orthogonal. Information in relational databases like SQL Server is described using relational schema languages (i.e. SQL) however this hasn't stopped Microsoft from creating myriad ways to extract XML from SQL Server such as SQLXML, FOR XML queries and  the .NET Framework's DataSet class which information stored in relational databases to interoperate directly with SOAP payloads and XML documents. No one would claim that the fact that the data in a relational database is not defined using W3C XML Schema (or RELAX NG) makes it impossible to extract XML from a relational database or view it as an XML data source. WinFS is no different.

It's troubling, though, that the architects must be consulted to find out whether Longhorn's "Windows types" will be transferable to standards-based software.

I don't work on WinFS so there was no chance I'd make a definitive statement about what features they plan to support or not. This is simply common sense on my part  not an indication one way or the other about the degree of XML support in WinFS. With any luck I'll soon be able to get one of the WinFS folks to start blogging and then more accurate information can be gotten from the horses mouth.