Is there a formal basis for XML? For XML Schema?

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

It is my understanding that underlying the functional programming languages Haskell, Scala, and XSLT is Lambda Calculus. Those languages are simply a layer of abstraction (syntactic sugar) on top of Lambda expressions. 

The field of Lambda Calculus is formal and rich and enables powerful properties of Lambda expressions to be proven. 

A functional program may be translated to Lambda expressions. Then, Lambda Calculus may be employed to prove powerful properties about the program.

Thus, Lambda Calculus is the formal basis for Haskell, Scala, and XSLT.

Is there a formal basis for XML?

Is there a formal basis for XML Schema?

/Roger