UML Activity Diagram Notation — Elements

(1) Filled circle,The start of a process

(2) Filled circle inside a larger circle,The end of a process

(3) Rectangle with rounded corners,An activity (a specific subprocess that must be carried out)

(4) Solid bar,Activity coordination — all incoming activities must complete before the process continues, or outgoing activities may execute in parallel

(5) Arrow annotated with [condition],A guard — the flow is only followed when the condition in square brackets is true

Explanation

UML activity diagram elements: a filled circle = start; filled circle inside outer circle = end; rounded rectangle = activity; solid bar = synchronization (fork/join) — when flow from more than one activity leads to a solid bar, all must complete before progress; when flow from a solid bar leads to activities, those may run in parallel; annotated arrow with [condition] = guard specifying when that flow is followed.

Symbol	Notation Title	Meaning & Description
	Filled circle	Represents the start of the activity workflow.
	Filled circle inside outer circle	Represents the end of the activity workflow.
	Rounded rectangle	Represents an individual activity or action step within the process.
	Solid bar	Represents synchronization, which handles concurrent behaviors through two structures: Join: When flows from more than one activity lead to the solid bar, all incoming activities must complete before progress can continue. Fork: When a flow splits out from a solid bar into multiple activities, those subsequent actions may run in parallel.
	Annotated arrow with [condition]	Acts as a guard condition, specifying that the corresponding control flow is only followed if the criteria inside the brackets evaluates to true.