A Merge Node brings together a number of alternative flow paths in Activity, Analysis and Interaction Overview diagrams. For example, if a Decision is used after a Fork, the two flows coming out of the Decision must be merged into one before going to a Join; otherwise, the Join waits for both flows, only one of which arrives.
A Merge Node has multiple incoming edges and a single outgoing edge. The edges coming into and out of a Merge Node must be either all object flows or all control flows.
- Activity Diagram
- Analysis Diagram
- Interaction Overview Diagram
- Object Flow
- Control Flow
OMG UML Specification:
The OMG Unified Modeling Language specification, (v2.5.1, p.427) states:
A merge node is a control node that brings together multiple alternate flows. It is not used to synchronize concurrent flows but to accept one among several alternate flows.