TY - RPRT A1 - Batory, Don A1 - Höfner, Peter A1 - Möller, Bernhard A1 - Zelend, Andreas T1 - Features, modularity, and variation points N2 - A feature interaction algebra (FIA) is an abstract model of features, feature interactions, and their compositions. A structured document algebra (SDA) defines modules with variation points and how such modules compose. We present both FIA and SDA in this paper, and homomorphisms that relate FIA expresssions to SDA expressions. Doing so separates fundamental concepts of Software Product Lines (SPLs) that have previously been conflated and misunderstood. Our work also justifies observations and relationships that have been used in prior work on feature-based SPLs. Y1 - 2021 UR - https://opus.bibliothek.uni-augsburg.de/opus4/frontdoor/index/index/docId/91213 UR - https://nbn-resolving.org/urn:nbn:de:bvb:384-opus4-912130 N1 - Technical Report, October 2013 PB - University of Texas at Austin CY - Austin, TX ER -