nivel2: A web-based multi-level modelling environment built on a relational database

We introduce the nivel2 software for multi-level modelling. Multi-level modelling is a modelling paradigm where a model element may be simultaneously a type for and an instance of other elements under some constraints. This contrasts traditional modelling methods, such as the UML, where an element may not be a class and an object simultaneously. In contrast with previous approaches to multi-level modelling, the nivel2 software utilises an industrial scale relational database for data storage and reasoning. Further, a web-based user interface is provided for viewing and editing models. The architecture enables multiple users in different roles working on the same models at various levels of abstraction at the same time.