Multi-level modeling with XML

Multi-level modeling offers substantial advantages when expressing complex domain concepts, and it comes with the promise to allow a fine-grained reuse and extensibility of (domain-specific) modeling languages on different levels of conceptual abstractions. A small number of tooling environments have been proposed that support multilevel modeling. However, in order to be able to unleash the potential of multi-level models as widely accepted means to formally define complex concepts, and to realize the promises of reusability and extensibility, a representation format for multi-level models is required, which is easy to understand for modeling experts, and is independent from any specific tooling environment. This paper proposes design principles of an XML format for representing multi-level models as XML documents. The approach is realized as a lightweight extension to the XML Schema Definition (XSD) standard, using built-in XML language extension mechanisms. The implementation of a multi-level schema validator is provided as a proof of concept.