“What Happened to my Models?” History-Aware Co-Existence and Co-Evolution of Metamodels and Models

Metamodels like many other software artifacts, are expected to evolve and exist in different versions. Consequently, the instances of these metamodels (models), become invalid and need fixing. The usual strategy for this is adapting models based on changes made to the metamodels, i.e., co-evolution. However, co-evolution usually adopts an all-or-nothing strategy that overlooks three important aspects: (a) preserving the history of the metamodel, (b) preserving the model's history before the co-evolution, and (c) supporting models to co-exist for different metamodel versions and delay their co-evolution. These aspects lead to problems for maintaining models in practice since often co-evolution gets driven by customer needs, e.g., the customer decides when to update. In this paper, we propose a novel approach that allows the creation of a metamodel version and records the history of metamodels and models by adopting an operation-based infrastructure. These metamodel versions allow engineers to delay the co-evolution of certain models by having co-existing metamodel versions. This notion of co-existence, in addition to the operation-based infrastructure, helps to preserve the complete history of metamodel and models, i.e., the history before and after co-evolving a model. To evaluate our approach, we conducted an empirical study, where we co-evolved models of varying domains. The results show that our approach correctly records the history of the metamodel and model. Furthermore, we measured the performance during co-evolution while having all versions co-existing in the same space. It shows that in the worst case, our approach required 887.91 seconds to co-evolve a model with more than 88,000 elements and 2,000,000 properties.