hi!
i'm new to creating desktop applications. I've a working site in php with mysql support. I want to convert this site into a desktop application. Is Adobe AIR or Adobe Flex better? can i use php as such in both AIR and Flex? or should i convert them to xml or something which it uses?
AIR is Flex on the desktop... So... I suppose you mean whether you can use AIR with PHP? AIR/Flex should be able to handle whatever communication protocol you're using on the server.
Saying 'should i convert them to xml or something' is a bit nebulous.
I guess what you really asking is: Should I rewrite my application entirely in Adobe technologies or Can I/Should I integrate it with my existing PHP code.
I would recommend you expose the existing PHP functionality as RESTful web services and redo the user interface in Adobe AIR. That way you can leverage the existing site to make the desktop application. There is a ton of information of building applications like this, just research REST, SOA (service oriented architecture), SAAS (Software as a Service).
Adobe AIR/Flex is fine, especially if you want it to work on multiple operating systems, but the Application won't necessary have the looking and feel of its host desktop environment.
Adobe AIR is a runtime that adds to the capabilities of Adobe Flash Player to allow the creation of desktop applications.
Adobe Flex is a framework to build rich user interfaces. Flex applications are supported both in Flash Player and AIR.
This cannot be a question of one or the other. Flex can be used together with AIR. If you want a desktop app that allows you to use Adobe's Flash Platform technologies, definitely use AIR. If you want a set of pre-built UI controls to use in that AIR app, use Flex too!
You can communicate with PHP on your server in both Flash Player and AIR. PHP cannot be run directly in AIR. If you want the application to be entirely self-contained with no server, then you can't use PHP.