elipse : noClassDefFound : JPA class

I am using eclipse (eclipse link) for JPA simple application(standalone app). I have one java project which contains my main logic and I have written a JPA project which contains all my bean classes and a class with all static methods for insert and delete etc.

I am exporting jar of my main project but every time the line where first call to my JPA is written : fires an exception saying JPA-database class def not found. Where am I going wrong?(I have added the JPA project to classpath of main project)

this can be a stupid question, but I am new to JPA so, can JPA be part of JAR? or do I always need a war or ear file or in short a web based project?

thanks