A Sequence Flow is a connector which establishes an oriented relationship between two elements of a workflow (Activities, Events, and Gateways). The purpose of a sequence flow is to defines the execution order of workflow elements. In GO-BPMN, only the Normal Flow is supported with the Default Flow being considered a special case of Normal Flow.
A Normal Flow is a Flow type designating the execution order of the workflow elements. It connects a source and a target element in an oriented way: On execution, the flow pass from the source to the target element.
A source or target element of a Normal Flow can be Events, Activities, or Gateways.
If the source of a Normal Flow is an Exclusive Gateway, a Normal Flow can define a guard. A guard defines a Boolean condition, which has to be true for the Flow to be taken. If false, the execution is held by the Flow and the Flow guard is evaluated continuously.
A Default Flow is a special case of the Normal Flow which has an Exclusive Gateway as its source element. It is the last-resort Flow which is taken if not other Flows leaving an Exclusive Gateway can be taken: If conditions on guards of all other Flows prevent them from being taken, the Default Flow is used.