UML Activity Diagram

Activity Diagram⌘

• Describes the workflow behavior of a system, focuses on flows.
• A Process describes a sequence or flow of Activities in an organization with the objective of carrying out work.

Activity, Action⌘

Activity

• describes a sequence of actions based on control models and object flow models
• contains edges and activity nodes (e.g. actions)
• represented by a rectangle with rounded corners

Action

• is a fundamental unit of executable functionality contained within an Activity
• represents a single step within an activity

Activity ⌘

Activity contains nodes:

• Action
• Object
• Control Node

and edges:

• Control Flow
• Object Flow

Control Flow⌘

• A control flow is an edge that starts an activity node after the previous one is finished

Object Flow⌘

OR

• An object flow is an activity edge that can have objects or data passing along it

Objects⌘

• Incoming or outgoing objects are parameters
• Placed (as rectangles) on the border

• Or as small rectangle, called a pin (input or output)

Token⌘

• The semantics of an activity is based on a token flow
• Control tokens and object tokens flow between nodes over edges

Activity Example⌘

Initial Node⌘

• It has outgoing edges but no incoming edges
• An activity may have more than one initial node
  • Each generates a concurrent flow
• An initial node can have more than one outgoing edge
  • Semantics: a control token at each outgoing edge
• Activity diagrams do not have to have initial nodes
• Notation: a filled circle

Final Node⌘

• An activity may have more than one activity final node
• The first one reached stops all flows in the activity
  • Regardless of the number of tokens in activity
• At least one incoming edge and no outgoing edges
• If several incoming edges only one must carry a token
• Activity diagrams do not have to have final nodes
• Notation: a filled circle with an outer ring

Decision⌘

• is a control node that chooses between outgoing flows
• One incoming edge and several outgoing edges
• When a token is supplied guards on outgoing edges are evaluated
  • Token goes to first true outgoing
• Notation: a rhombus

Merge⌘

• A merge node is a control node that brings together multiple alternate flows
  • It is not used to synchronize concurrent flows
• Several incoming edges, one outgoing edge
• Nothing calculated, nothing expected
• Notation: an empty rhombus

Fork, Join⌘

• Fork – one incoming edge and multiple outgoing edges
• Join – multiple incoming edges and one outgoing edge

Implicit splitting⌘

Once action A terminates

• a control token is available at both outgoing edges
• actions B and C start concurrently

Implicit synchronization⌘

Action F doesn't start until tokens are available at both incoming edges - actions D and E have to terminate

Implicit split/synchronization - object flow⌘

AND semantics for object flows

• Once action A terminates it provides two object nodes
• Action F doesn't start until object tokens are available at both incoming edges - actions D and E have to terminate