The XML team has recently started getting questions about our position on XQuery 1.0, XPath 2.0 and XSLT 2.0. Yesterday my boss, Mark Fussell, posted about why we have decided to implement XQuery 1.0 but not XSLT 2.0 in the next version of the .NET Framework. Some people misinterpreted his post to mean that the we chose to implement XQuery 1.0 over XSLT 2.0 because we prefer the syntax of the former over that of the latter. However decisions of such scale aren't made that lightly.

There are several reasons why we aren't implementing XSLT 2.0 and XPath 2.0

It takes a lot of effort and resources to implement all 3 technologies (XQuery, XSLT 2.0 & XPath 2.0). Our guiding principle was that we believe creating a proliferation of XML query technologies is confusing to end users. We'd rather implement one more language that we push people to learn than have to support and explain three more XML query and transformation languages, in addition to XPath 1.0 & XSLT 1.0 which already exist in the .NET Framework. Having our customers and support people have to deal with the complexity of 3 sophisticated XML query languages two of which are look similar but behave quite differently in the case of XPath 2.0 and XQuery seemed to us not to be that beneficial. 

XPath 2.0 has different semantics from XQuery, XQuery is strongly and statically typed while XPath 2.0 is weakly and dynamically typed. So it isn't simply a case that if you implementing XQuery means that you can simply flip some flag and disable a feature or two to turn it into an XPath 2.0 implementation. However all of the use cases satisfied by XPath 2.0 can be satisfied by XQuery. In the decision to go with XQuery over XSLT 2.0, Mark is right that we felt that developers would prefer the familiar procedural model and syntax of XQuery to the template based model and syntax of XSLT 2.0. Most developers working with XSLT try to use it as a procedural language anyway, and don't really harness the power of templates. There's always the steep learning curve until you get to the “Aha“ moment and everything clicks. XQuery with its FLWOR construct and user defined functions fits more naturally with how both programmers and database administrators access and manipulate data than does XSLT 2.0. Thus we feel XQuery and not XSLT is the future of XML based query and transformation. 

This doesn't mean that we will be removing XSLT 1.0 or XPath 1.0 support from the .NET Framework. It just means that our innovation and development efforts will be focused around XQuery going forward.