Field Types for Deep Characterization in Multi-Level Modeling

Traditional two-level modeling approaches distinguish between class- and object features. Using UML parlance, classes have attributes which require their instances to have object slots. Multi-Level Modeling unifies classes and objects to "clabjects", and it has been suggested that attributes and slots can and should be unified to "fields" in a similar way. The notion of deep instantiation for clabjects creates the possibility of "deep fields", i.e., fields that expand on the roles of pure attributes or pure slots. In this paper, we discuss several variants of such a "deep field" notion, pointing out the semantic differences and the various resulting trade-offs. We hope our observations will help clarify the range of options for supporting clabject fields in multi-level modeling and thus aid future MLM development.