NOTE:Remember dont copy unnecessary files and open them in your project. Because when you will run even your HelloWorld page, all these will try to compile and will give you thousands of errors...
Never solve these errors, as they don't exist at all. They are coming just because we have done something wrong....
(mds:Meta Data Service)
You can follow article "JDeveloper Setup for OA Framework" to config JDEV,
Except above note, in project properties remove select compiler and in java uncheck the xml validation (it will throw error while compiling)
Path: Project Properties -> Compiler -> XML -> Uncheck XML Syntax on Make
Now run the page you want, it will mostly work...
Forgot one thing, Keep patient, Run OAF files locally, This process(Compiling + OC4J Launching + OAF Page Open) may need long time,depends on your hardware,Enjoy,PTIAN