How unique is XAML?

Question

Was talking to a colleague about XAML and how it is both a presentation and object description language and therefore quite unique and novel among IT technology.

Is this true that XAML is unique and novel?

Does XAML have any counterparts or predecessors in the Java world or elsewhere? I believe someone told me that Java Server Faces was similar to WPF, so what is the equivalent of XAML there?

I know MXML in Flex is similar but as far as I can remember there are some major structural differences, from what I remember MXML doesn't really describe objects but is more of a pure presentation XML.

Answer 1

This is a case of a general technology having such an overwhelming common specific usage that becomes synonmous with the specific usage. For example, discussions of Javascript often assume the browser context and the manipulation of a HTML DOM without anyone having to expressly say so.

Strictly speaking XAML is not like XUL or SVG apart from being XML. XUL, SVG have a defined syntax for declaring User interface or graphical elements, raw XAML does not.

XAML can, for example, also be used to describe Workflows in Workflow foundation.

XAML is actually an approach to reading XML in order to describe types and properties of those types. For example, a property of a type may be described either using an attribute or an Element as long as its name can be interpreted correctly. XAML also includes an extension to the basic XML syntax where { } in an attribute can act as a short hand for a complex element.

I've not come across this sort of thing before. All other XML based technologies come with a specific purpose, XAML is the first usage of XML I've seen that is deviod of any specific nomenclature but just a means of mapping XML to types.