This work is a study and overview intended to investigate commonalities and differences between various modeling approaches that are either explicitly referred to as ‘declarative’, follow the same principle, or share a very similar idea. Consequently, a unifying comparison concept in the form of three classification models is developed in order to have a system that allows for a better overview, understanding, and comparison of the investigated approaches. The main goal behind this work was orignally the investigation of the research question of whether there already is or is not an explicit approach for using declarative process models as formal specification for less abstract or imperative process models outside a very specific application concept in the domain of subject-oriented modeling. As a side effect, this work also provides a domain overview and a systematic approach to better understand the underlying concepts.