title: UML Sequence Diagram Example Sys_A -> Sys_B: sync request (solid arrowhead) note: this is a note Sys_B --> Sys_A: response (dashed line) note: this is a multiline note Sys_B -o> Sys_C: async request (open arrowhead) Sys_B -> Sys_B: calling myself frame/loop: while some flag != false { Sys_A -> Sys_B: call in a loop } frame/alt: if some condition == True { Sys_A -> Sys_B: call on True cond: else Sys_A -> Sys_C: call on False } frame/opt: this call is purely optional { Sys_A -> Sys_D: purely optional call }