In a collaboration template's activity diagram, the line that indicates control flow between two nodes. If more than one outcome is possible between the nodes, each outcome is represented by a different transition link that leads to a different execution path. Each transition link may have an associated condition that is evaluated at runtime. Flow passes along the transition link whose expression evaluates to true. If the nodes have a single transition link, its condition is assumed to be true. See also control flow, exception transition link, normal transition link.