Handling the various derivations of a product can be a daunting (and costly) task. To tackle this problem, we propose a method based on the use of creational design patterns to uncouple the variations (reified as language-level objects) from the selection process. This makes it possible to automatically derive a given product from the set of all possible ones, and to specialize its code accordingly. The contribution of this paper is to propose architectural constraints for Product Line expressed in UML as meta-level OCL constraints, providing a set of patterns for modeling variability issues of a Product Line Architecture in the context of the OMG's Model Driven Architecture, and explicit the use of OCL2 transformations combined together using the UMLAUT framework to automate the derivation process.