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
in industrial context is infeasible, calling for an automated
approach.

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 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 twenty-two 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. Using R, we position H in an
absolute perspective, rather than relatively to a case study. 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.