BPMN provides modelers with the capability of showing additional information about a Process that is not directly related to the Sequence Flows or Message Flows of the Process.
— BPMN 2.0.2 Standard, 8.4.1, Artifacts
Artifacts provide additional information that modelers add to bring a necessary level of detail to the diagram. Artifacts do not directly add any runtime behavior but serve to make the model clearer.
Annotations are a mechanism for a modeler to provide additional information for the reader of a BPMN Diagram.
— BPMN 2.0.2 Standard, 8.4.1, Text Annotations
Data Object elements MUST be contained within Process or SubProcess elements. Data Object elements are visually displayed on a Process diagram. Data Object References are a way to reuse Data Objects in the same diagram. They can specify different states of the same Data Object at different points in a Process.
— BPMN 2.0.2 Standard, 10.4.1, Data Objects
Groups are often used to highlight certain sub clauses of a Diagram without adding additional constraints for performance, as a Sub-Process would. The highlighted (grouped) sub clause of the Diagram can be separated for reporting and analysis purposes. Groups do not affect the flow of the Process.
— BPMN 2.0.2 Standard, 8.4.1, Groups