Apples and oranges: comparing top-down and bottom-up language product lines

Over the past decade language development tools have been significantly improved. This permitted both practitioners and researchers to design a wide variety of domain-specific languages (DSL) and extensions to programming languages. Moreover, multiple researchers have combined different language variants to form families of DSLs as well as programming languages. Unfortunately, current language development tools cannot directly support the development of these families. To overcome this limitation, researchers have recently applied ideas from software product lines (SPL) to create product lines of compilers/interpreters for language families, denoted language product lines (LPL). Similar to SPLs, however, these product lines can be created either using a top-down or a bottom-up approach. Yet, there exist no case study comparing the suitability of both approaches to the development of LPLs, making it unclear how language development tools should evolve. Accordingly, this paper compares both feature modeling approaches by applying them to the development of an LPL for the family of role-based programming languages and discussing their applicability, feasibility and overall suitability for the development of LPLs. Although one might argue that this compares apples and oranges, we believe that this case still provides crucial insights into the requirements, assumptions, and challenges of each approach.