Sorry, I said I'd write this over a week ago. Don't the weeks fly by though. It seems I blink on Monday and then it's Friday. Oh, the treadmill of life.

In the mean time Ferdy has written on the topic of when using RIA is the right choice. It's the kind of in-depth article only a man without three children could write. Worth a read if you get chance. Ferdy sums it up fairly well:

My claim is that RIA technology is justified when the interaction requires it

In essence, as Ferdy noted, there isn't really any clear way to decide whether to use RIA or not. It all depends.

For those of you wondering what RIA is, it's Rich Internet Applications and is primarily Flex, but also things like Silverlight.

Once you fall for the lure of RIA it's all too easy to see how it could fit any problem and just use it for everything. That's bad.

Just as important as knowing when to use it is knowing when not to (which is the same thing I guess).

• Don't use RIA if you don't need to.
• Don't use RIA if you aren't sure the audience will always be able to.
• Don't use RIA for a plain website just because you think it will make it look cooler.
• Don't use RIA if you want the site to be reliably indexed by Google et al.

Sorry I can't offer anything more definitive. There just isn't a definitive guideline to follow. Working, as I do, alone, I have the luxury of making the call in most cases, so have never needed think about it to such a degree.

Mixing The Two

As we speak I'm working on a website that mixes both RIA and traditional web technologies. The site allows children of school-going age to create posters about their experience with the outdoors and nature. They can browse existing posters using a normal HTML-based website. If they want to make their own then they register and login using normal HTML forms and then up pops a Flex-based app in a new window.

I could probably have done the whole site in Flex, so that they browse entries, register and login via Flex too. I didn't need to though, so I didn't.

On the flip side I probably could have created a poster-making app in pure HTML. It would have been a nightmare of a job though, not been as nice a product and taken four times as long to do it. So I chose RIA.