systemcomposer.activity.Flow

Flow between activity nodes

Since R2026a

Description

A Flow object defines the flow between a source node and a destination node.

Creation

Create a flow in an activity diagram using the connect function.

action1 = addNode(activity,'action1','action');
action2 = addNode(activity,'action2','action');
flow1 = connect(action1,action2);

Properties

Name — Name of flow

character vector

Name of the flow, specified as a character vector.

Example: flow1

Data Types: char

Guard — Guard expression

boolean expression

Guard expression to be evaluated for decision node, specified as a Boolean expression. To access the token flowing through the flow, use the built-in keyword token.

Example: token >= 1

EvaluationOrder — Order of evaluating guard expression

positive integer

Order of evaluating guard expression for decision node, specified as a positive integer.

Parent — Activity that contains flow

activity object

Activity that contains the flow, specified as a systemcomposer.activity.Activity object.

FlowType — Type of flow

control (default) | object

Type of flow, specified as control or object.

SourceNode — Source node for flow

activity node object

Source node for the flow, specified as a systemcomposer.activity.ActivityNode object.

DestinationNode — Destination node for flow

activity node object

Destination node for the flow, specified as a systemcomposer.activity.ActivityNode object.

Model — Parent activity diagram model

model object

Parent activity diagram model, specified as a systemcomposer.activity.Model object.

SimulinkHandle — Simulink handle

double

Simulink^® handle, specified as a double.

This property is necessary for several Simulink workflows and for using Requirements Toolbox™ programmatic interfaces.

Example: handle = get(object,'SimulinkHandle')

Data Types: double

UUID — Universal unique identifier

character vector

Universal unique identifier, specified as a character vector.

Example: '91d5de2c-b14c-4c76-a5d6-5dd0037c52df'

Data Types: char

ExternalUID — Unique external identifier

character vector

Unique external identifier, specified as a character vector. The external ID is preserved over the lifespan of the element and through all operations that preserve the UUID.

Data Types: char

Object Functions

addProperty	Define custom property for stereotype
changeStereotype	Change currently applied stereotype to new stereotype in its stereotype hierarchy
destroy	Remove model element
getEvaluatedPropertyValue	Get evaluated value of property from element
getFlow	Get flow from activity diagram
getProperty	Get property value corresponding to stereotype applied to element
getPropertyValue	Get value of architecture property
getStereotypeProperties	Get stereotype property names on element
getStereotypes	Get stereotypes applied on model element
hasProperty	Find if element has property
removeStereotype	Remove stereotype from profile
setProperty	Set property value corresponding to stereotype applied to element
applyStereotype	Apply stereotype to model element
hasStereotype	Find if element has stereotype applied

Examples

Create Activity Diagram Programmatically

This example shows how to create an activity diagram programmatically. An activity diagram describes system behavior that models the flow of tokens from inputs to outputs through a controlled sequence of actions. You can use activity diagrams to conceptualize a system, visualize functional flow through actions or decisions, and understand how system components interact with one another. To learn more about authoring activity diagram, see, Author a Simple Activity Diagram.

In this example, you create an activity diagram to illustrate the steps involved in placing an order, checking inventory availability, and canceling the order if items are unavailable.

Create New Activity Diagram

Create a new activity diagram named AuthorActivity using the systemcomposer.createActivity function.

activityName = 'AuthorActivity';
adModel = systemcomposer.createActivity(activityName,true);
activity = adModel.Activity;

Add Initial Node and Action Nodes

Add an initial node and required action nodes using the addNode function.

init1 = addNode(activity,'init1','initial');
action1 = addNode(activity,'Place Order','action');   
action2 = addNode(activity,'Authorize Payment','action');  
action3 = addNode(activity,'Check Inventory','action');  
action4 = addNode(activity,'Cancel Order','action');  
action5 = addNode(activity,'Fulfill Order','action'); 

Define Action Node Behavior and Add Pins

Add the behavior type of an action node using the setBehaviorType function. You can specify the MATLAB® functions for an action node with a behavior type of MATLAB by using the BehaviorDefinition property.

setBehaviorType(action1,'MATLAB');
action1.BehaviorDefinition = 'PlaceOrder';
setBehaviorType(action2,'Activity');
setBehaviorType(action3,'MATLAB');
action3.BehaviorDefinition = 'CheckInventory';

You can add pins on an action node using the addNode function. For more information on pins, see Pin.

outPin1 = addPin(action1,'order','out');
inPin1 = addPin(action2,'order1','in');
outPin2 = addPin(action2,'order2','out');
inPin2 = addPin(action3,'order3','in');
outPin3 = addPin(action3,'order4','out');
inPin1.IsStreaming = true;
outPin2.IsStreaming = true;

Create Nested Activity

You can create a nested activity for an action node with Activity behavior type.

childActivity = action2.ChildActivity;
childAction1 = addNode(childActivity,'Enter Card Details','action');
childAction2 = addNode(childActivity,'Authenticate Details','action');

Add Control Nodes

Add a join or fork node and a merge or decision node. For more information on control nodes, see systemcomposer.activity.ControlNode.

jfork = addNode(activity,"jfork","joinfork"); 
decMerge1 = addNode(activity,"decMerge1","mergedecision");
decMerge2 = addNode(activity,"decMerge2","mergedecision");

Add Flow Final and Activity Final Nodes

Add a flow final node and an activity final node.

ffinal = addNode(activity,"ffinal","flowfinal");
afinal = addNode(activity,"afinal","activityfinal");

Connect Flows

Connect the flows to complete the activity diagram. You can create guard expressions for flows that output from decision node.

flow1 = connect(init1,action1);
flow2 = connect(outPin1,jfork);
flow3 = connect(jfork,inPin1);
flow4 = connect(jfork,inPin2);
flow5 = connect(outPin2,decMerge1);
flow6 = connect(outPin3,decMerge2);
flow7 = connect(decMerge2,action5);
flow8 = connect(decMerge2,action4);
flow9 = connect(decMerge1,action5);
flow10 = connect(decMerge1,action4);
flow11 = connect(action4,ffinal);
flow12 = connect(action5,afinal);

Create guard expression for flows that output from decision node.

flow7.Guard = 'token == 1';
flow8.Guard = 'token == 0';

You can use the Simulink.BlockDiagram.arrangeSystem function to improve the layout of the activity diagram model.

Simulink.BlockDiagram.arrangeSystem('AuthorActivity');

More About

Definitions

Term	Definition	Application	More Information
Activity	An activity describes system behavior that models the flow of tokens from inputs to outputs through a controlled sequence of actions. An activity diagram contains action nodes with pins connected by flow lines.	Use activity to conceptualize a system, visualize functional flow through actions or decisions, and understand how system components interact with one another.	Describe System Behavior Using Activity Diagrams Create New Activity Diagram
Token	Tokens are objects that flow in the activity diagram. A token can represent data such as structures and integers, or a token can simply pass on the control.	An object token represents an object, such as a piece of data. A control token represents a control or a triggering event that does not carry any data.	Use Control Nodes to Manipulate Token Flows Use MATLAB Action Node Without MATLAB Function to Initialize Object Token
Action node	An action node is a key building block in an activity diagram. An action node represents an action to be executed. Action nodes consume input tokens and produce output tokens on pins.	Use a MATLAB® function or a nested activity diagram to describe the behavior of an action node.	Author Action Node with MATLAB Function Behavior Use Nested Activity to Describe Action
Control node	A control node routes a logical flow of tokens through the system.	Use control nodes and flows to route tokens. Control nodes can be used to initialize, split, merge, and terminate token flows.	Use Control Nodes to Manipulate Token Flows
Pin	A pin acts as a buffer for object tokens and directs tokens into or out of an action node. The directionality of the pin represents input or output. You can connect pins by object flows.	Use pins to route an object token to or from an Action Node. Pins are also used to store object tokens before or during execution. You can use pins only for object flows.	Author a Simple Activity Diagram Types Editor
Type	A type defines the contents of a token that flows through a pin. A type has dimension, unit, complexity, minimum, maximum and description.	A value type token is a type assigned to a single value. A composite type token is equivalent to a bus structure that contains field of different values and data types. A MATLAB class type token references a MATLAB class on the path that defines a complex object with properties and methods. You can use a built-in MATLAB class or define your own MATLAB class.	Action Node Types Editor Model Complex Objects in Activity Diagrams Using MATLAB Class Tokens
Parameter node	A parameter node routes tokens into or out of a nested activity diagram. When a pin is created, a corresponding parameter node will be created inside the nested activity.	Use a parameter node to define how tokens enter or leave a nested activity. There are two types of parameter nodes input and output.	Use Nested Activity to Describe Action
Flow	A flow in an activity diagram connects two nodes. A dashed line represents a control flow. A solid line represents an object flow.	Tokens in an object flow contains token data on which actions operate. You can use object flows to route input or output tokens to carry information or physical items between object nodes. Tokens in a control flow trigger the execution of actions. You can use control flows to model transfer of control from one Action Node to another.	Simulate, Visualize, and Validate Activity Diagrams

Version History

Introduced in R2026a