BPMN diagrams consist of two main types of elements: nodes and connections. The majority of BPMN elements are nodes, which are grouped into: Flow Objects, Data, Swim lanes and Artefacts. The remaining BPMN elements are connections, which are represented with one of the BPMN connecting objects.
BPMN 2.0 defines four basic types of connecting objects: Sequence Flows, Message Flows, Data Associations and Associations.
The most common connections are Sequence Flows which are represented with directed solid lines. Sequence Flows define the order of flow elements in a process diagram and a choreography diagram. A sequence flow defines a process’s behaviour or control flow. A Sequence Flow can also define a condition when represented with a mini-diamond. Sequence flows can only be used within a process and cannot cross the boundary of a pool.
In contrast a Message Flow is used to show the flow of messages between two participants that are able to send and receive them. In BPMN, two Pools will represent the two Participants. The sources of message flows can be pools, events, and activities, and the targets are represented by corresponding elements.
Data Associations are used to show the flow of information between data objects, stores, inputs, and outputs. Data associations are directed dotted lines, which define the order of data flow. Data objects may also be directly associated with a Sequence Flow to represent the same input/output relationships.
The last type of a connecting object is association, which has the same graphical representation as data association. Associations are used to link BPMN’s artifacts with other BPMN elements, and are most commonly used to connect a Text Annotation with activity, gateway or event. If there is a reason to put directionality on the Association then a line arrowhead may be added to the Association line.Business Process Analysis BPMN Video