Long time without a blog entry, but I’m back More on this later.

Adobe obviously hasn’t done a very good job at getting this across and Microsoft’s relative silence suggests it is possibly enjoying the confusion. Numerous so-called ‘experts’ out there keep mentioning AIR and Silverlight as competing directly in the RIA space. It’s an easy trap to fall into, as we shall see. A whole new crop of these popped up this week with the announcement of Mozilla Prism which, depending on how you look at it, is either a genius move by Mozilla or totally cheating seeing as all it currently does is pretend to be a desktop app by removing buttons from the Firefox browser.

So here’s my attempt at explaining the differences….

AIR
Desktop applications, can work online or offline, created (important this) in Javascript/HTML or Flex/Flash if you like (for added UI polish and none of that flickery DHTML stuff). Can render web pages, PDFs and Flash content. Applications have an installer/uninstaller and a desktop icon and support some desktop functionality like drag and drop, system tray etc.

Flash
Browser plug-in (although Flash apps can be also be ported to desktop via AIR), animation, interactivity, powerful graphics manipulation, video streaming delivery platform, now with H.264 support too. Uses Actionscript.

Flex
Uses Flash runtime (and like Flash can also easily be ported to AIR on the desktop), but much more robust application development tools and some clever (but expensive) back-end capabilities, talking to Java etc. (but doesn’t quite do authentication with file uploads properly thanks to a quirk in the Flash player, much to the amusement of every Java developer I work with). Uses MXML and Actionscript.

Silverlight
Promising Flash alternative, animation, interactivity, powerful graphics manipulation, except that perhaps unsurprisingly it has a few MS-centric features and although it does video well doesn’t have H.264 support and 90% penetration, uses .NET tools/workflow, XAML, C# – similar kind of model to Flex.

WPF
Stands for Windows Presentation Foundation, the real AIR rival, alongside Prism (which cheats, albeit elegantly). Silverlight is a subset of WPF/E, kind of what Flash is to AIR I guess. Applications run on desktop with access to DirectX, system functions etc.

Prism
Firefox without the buttons, plus a desktop icon so it looks like a desktop application but is really a browser page/application pretending to be a desktop application. Arguably all you need though, hence accusations of evil genius. At the moment making a desktop shortcut to the GMail address and hitting F11 in IE has much the same effect but this approach actually promises much once Firefox 3 and things like Canvas and other new HTML features come along.

So next time you feel compelled to compare, it’s sort of like this, only more complicated:

Sliverlight is an alternative to Flash
WPF is an alternative to AIR
Prism is a modified browser that provides a desktop ‘experience’ similar to AIR and WPF