Optional Activities in Process Flows

A drawback of many business process modelling languages (BPMLs) is that modalities are implicitly expressed through the structure of the process flow. All activities are implicitly mandatory and whenever something should be optional, the process flow is split to offer the possibility to execute the activity or to do nothing. This implies that the decision whether to execute one or more activities is described within another element, such as a gateway. The separation of decision and execution requires additional modelling elements and a comprehensive understanding of the entire process to identify mandatory and optional activities. In this paper, we address the problem and present an approach to highlight optionality in BPMLs based on the Control-Flow Patterns. Furthermore, we study the semantics of explicitly optional activities and show how to apply the general approach to a concrete BPML like the Business Process Model and Notation (BPMN). An explicitly optional activity is deemed to be more intuitive and also positively affects the structural complexity and the understandability of the process flow as shown by a graph transformation approach and a case study.