"Clafer: unifying class and feature modeling" available on-line in Software & Systems Modeling journal

The paper (available from publisher's website) presents formal semantics of Clafer. It precisely explains how a single modeling construct (clafer) can play roles of features, feature groups, classes, attributes, references, associations, and association classes. The paper also explains inheritance, specialization, extension, and redefinition. The semantics is presented in a structure preserving way, that is, the shape of the model is preserved in its semantics, rather than being flattened into a multitude of FOL formulas.