Automatic refactoring of delta-oriented SPLs to remove-free form and replace-free form

Delta-oriented programming (DOP) is a flexible transformational approach to implement software product lines (SPLs). In delta-oriented SPLs, variants are generated by applying operations contained in delta modules to a base program. These operations can add, remove or modify named elements in a program (e.g. classes, methods and fields in a Java program). This paper presents two notions of normal form for delta-oriented SPLs. Both normal forms do not contain the remove operation. Additionally, the second normal form enforces a limitation on the use of the method-modify operation. For each of the proposed normal forms an algorithm for refactoring a delta-oriented SPL into one that satisfies that normal form is described. The algorithms are formalized for a core calculus for delta-oriented SPLs of Java programs.