A Complete Operator Library for DSL Evolution Specification

Domain-specific languages (DSLs) allow users to model systems using concepts from a specific domain. Evolution of DSLs triggers co-evolution of models developed in these languages. Manual co-evolution of the thousands of models is unfeasible, calling for an automated support. A prerequisite to automating model co-evolution with respect to DSL evolution is the ability to formally specify DSL evolution, e.g., using predefined evolution operators. Success or failure of the practical application of the operator-based approach therefore depends heavily on the operators offered by the operator library at hand. In this paper we evaluate the completeness of the state-of-the-art operator library claimed to be "practically complete" (which we denote as H) by using it to specify evolution of an ecosystem of 22 commercial DSLs over the period of four years. We observe that 11% of the changes cannot be specified. However, there is no guarantee that extending the library with the identified deficiencies will be sufficient to specify evolution of other DSLs. To mitigate this, we design a theoretically complete library of operators, R. We observe that 77% of the operators from R are absent from H. Of the deficiencies in H, 72% could not be revealed by means of studying the extensive industrial ecosystem above. Our study suggests that the existing operator libraries are not extensive enough to specify evolution of large model-driven software ecosystems. Since extending operator libraries on a per-case study basis does not yield satisfactory results so far, we advocate an alternative, i.e. a theoretically complete library of operators R.