I'm interesting in understanding REST better than I currently do. I think using RubyonRails and Flex in the way described in the following article is a good example of a RESTful api. Because the middle-tier calls are simply calls to a URL and that URL simply provides data in an XML format. Rails is an excellent choice for this type of api/data exchange. This is really worth the read....

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Liverail - RubyOnRails (1.1) and Flex (2.0): Pt 1