XAML / Avalon Part 1.

Over the next few posts I'm going to cover what XAML is, how it fits in with current UI toolkits / web standards, and what the implications are for app development on Windows in the future.

Most devs are probably already aware that "Longhorn" is the codename for the next version of Windows, and that "Avalon" is the codename for the user services layer. "Avalon" is essentially a vector graphics engine which will allow for extremely rich GUIs that, when released, will make today's applications look like something from the stone age. Originally, MS declared that "Avalon" (& "Indigo", the comms layer that combines next generation web services with .net remoting-esque services) would only be available with "Longhorn". They've since backtracked, and downlevel versions both "Avalon" and "Indigo" will also be available on WinXP.

XAML (Extensible Application Markup Language, pronounced "zammel") is an XML dialect that developers will use to author applications for Longhorn. Currently, if you want to create an app, you have to decide on which platform to support - are you going thin or thick client? If thin, will you target devices as well, and which browsers will you support? XAML lets you define a single set of markup pages and code which can run as a standard installed desktop app, or run from a server; the platform choice you make now will essentially become a deployment choice. Your application source will remain the same, the UI if run through "Avalon" will be the same rich UI regardless. I've not gotten to the bottom of it yet, but I'm assuming that XAML will also render as HTML on downlevel browsers, in a similar way that ASP.NET mobile controls render different output based on the nature of the requesting device.

This is a big step change from the current model, where thick and thin clients run on different platforms and require mastery of completely different technologies and development techniques.

Next: more on XAML; what it looks like; XAML pages; the "Avalon" object model.