This paper addresses heterogeneity of business process metamodels and related interchange formats. The different approaches towards interchange format design and effects of interchange format specification are presented first. In particular completeness is identified as an important design criterion for interchange formats. Af- terwards the superset of metamodel concepts is extracted from 15 currently available XML-based specifications for business process modelling. Furthermore, these concepts are used as a framework for comparing the completeness of 15 specifications.