f96c6a36_EMF_v1_0_Users__Guide__Java
[Property] prefix [UML] prefix property is specified on the eCore page of the specification dialog for the UML Package. [XMI] prefix attribute7 [Java] 
The prefix part of the name of the Java package is the Java package that is specified on the package statement of the interfaces and/or classes contained in the package.
EMF v1.0 Users' Guide