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Elements of style of BPMN language

Several BPMN graphical tools support, at least partly, the OMG's BPMN specification. The BPMN standard is an essential guide for tools' makers when implementing the rules regarding depiction of BPMN diagrammatic constructs. Process modelers should also know how to rigorously use BPMN constructs when depicting business processes either for business or IT purposes. Several already published OMG's standards include the formal specification of well-formedness rules concern-ing the metamodels they address. However, the BPMN standard does not. Instead, the rules regarding BPMN elements are only informally specified in natural language throughout the overall BPMN documentation. Without strict rules concerning the correct usage of BPMN elements, no wonder that plenty of available BPMN tools fail to enforce BPMN process models' correctness. To mitigate this problem, and therefore contribute for achieving BPMN models' correctness, we propose to supplement the BPMN metamodel with well-formedness rules expressed by OCL invariants. So, this document contributes to bring together a set of requirements that tools' makers must comply with, in order to claim a broader BPMN 2 compliance. For the regular process modeler, this report provides an extensive and pragmatic catalog of BPMN elements' usage, to be followed in order to attain correct BPMN process models.