A software product line (SPL) is a family of software systems with well defined commonalities and variabilities. These systems (products) are uniquely identified by a set of features. But a feature is merely a label. To attach semantics to features, the code base for an SPL should be organized in some way to reflect which features correspond to which code.

Delta modeling is one approach towards bridging this gap. In a delta modeling code base, one can distinguish between a core implementation, containing the code common to each product, and deltas, containing code specific to some feature configuration(s). Deltas can make changes to the core in order to integrate one or multiple features. In this talk I present a new formalism generalizing the delta modeling approach, show some concrete examples and compare delta modeling to other approaches.