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Multi-level staged configuration (MLSC) of feature diagrams has been proposed as a means to facilitate configuration in software product line engineering. Based on the observation that configuration often is a lengthy undertaking with many participants, MLSC splits it up into different levels that can be assigned to different stakeholders. This makes configuration more scalable to realistic environments. Although its supporting language (cardinality based feature diagrams) received various formal semantics, the MLSC process never received one. Nonetheless, a formal semantics is the primary indicator for precision and unambiguity and an important prerequisite for reliable toolsupport.

We present a semantics for MLSC that builds on our earlier work on formal feature model semantics to which it adds the concepts of level and configuration path. With the formal semantics, we were able to make the original definition more precise and to reveal some of its subtleties and incompletenesses. We also discovered some important properties that an MLSC process should possess and a configuration tool should guarantee. Our contribution is primarily of a fundamental nature, clarifying central, yet ambiguous, concepts and properties related to MLSC. Thereby, we intend to pave the way for safer, more efficient and more comprehensive automation of configuration tasks.