A number of product family process frameworks has been published recently. These frameworks focus on different aspects of product family based development. We have investigated a variety of publicly available product family frameworks and chosen four of the variants for maximum coverage of different viewpoints. We first propose a reference product line process framework. With the help of the reference framework, the chosen source frameworks are correlated and compared at the level of individual activities. Both in the reference framework and in the comparison, we stress domain engineering as one of the most essential activities.