systemcomposer.interaction.Message

Message between lifelines in interaction

Since R2024a

Description

A Message object represents a communication between two lifelines of an interaction. On the sequence diagram representing the interaction, a message is shown as an arrow. Messages have labels that can describe the communication occurrence either formally or informally. A message corresponds to a connector connecting ports of two components in an architecture model.

An informal message label is written in natural language. A formal message label is in the form of trigger[constraint] where trigger represents the identifying event for this message, and constraint represents additional expressions that are expected to be true when this message occurs.

• For signal-based communication, a trigger is also called an edge and can described in the format direction(signal [+|-] value). You can enter a condition that specifies a triggering edge with a direction and an expression. The direction can be:

  • rising — The edge expression is rising from strictly below zero to a value equal to or greater than zero.

  • falling — The edge expression is falling from strictly above zero.

  • crossing — The edge expression is either rising or falling past zero.

• For message-based communication, a trigger can be described simply by using the name of the input message port, and represents the arrival of a message.

• For both signal and message-based communication, a constraint expression in square brackets on the message label is an optional MATLAB^® Boolean expression involving the names of the inputs to the destination lifeline.

Creation

Access Message objects via the RootFragment property of the corresponding systemcomposer.interaction.Interaction object. Iterate over the root fragment to inspect the systemcomposer.interaction.MessageEvent objects within the fragments. Access the Message property of the message event to inspect the corresponding Message object.

Properties

Type — Message type

"Signal" | "Message"

Message type, specified as one of the following options:

• "Signal" for signal-based communication.

• "Message" for Simulink^® message-based communication.

Data Types: string

Condition — Message label

string

Message label, specified as a string.

Data Types: string

Start — Start of message

message event object

Start of message, specified as a systemcomposer.interaction.MessageEvent object.

End — End of message

message event object

End of message, specified as a systemcomposer.interaction.MessageEvent object.

RelatedElements — Connectors represented by message

array of connector objects | array of physical connector objects

Connectors represented by message, specified as an array of systemcomposer.arch.Connector or systemcomposer.arch.PhysicalConnector objects.

UUID — Universal unique identifier

character vector

Universal unique identifier, specified as a character vector.

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

Data Types: char

Examples

Inspect Sequence Diagrams with Programmatic Interfaces

This example shows how to use read-only API workflows to navigate sequence diagrams in System Composer™ and display information about each of the elements.

Open Traffic Light Example

Open the traffic light example architecture model so that you can inspect the sequence diagrams visually and confirm the programmatic outputs.

model = systemcomposer.openModel("TLExample");

On the System Composer toolstrip, navigate to Modeling > Sequence Diagram to view the sequence diagrams associated with the model.

Programmatically Navigate Sequence Diagram

Collect the sequence diagrams represented by interactions that contain specific interactions of elements in the model.

interactions = model.getInteractions;

For the first interaction, extract the name of the sequence diagram.

disp("The first sequence diagram is called " + interactions(1).Name + ".")

The first sequence diagram is called SignalSequence.

For this sequence diagram, display each lifeline and the component the lifeline represents.

for i = 1:length(interactions(1).Lifelines)
    disp("The " + interactions(1).Lifelines(i).Name + ...
    " lifeline represents the " + ...
    interactions(1).Lifelines(i).RelatedElements.Name + ...
    " component.")
end

The ped lamp lifeline represents the ped lamp component.
The lampController lifeline represents the lampController component.
The poller lifeline represents the poller component.
The source lifeline represents the source component.

Now, display the contents of one message in the root fragment.

disp("The sequence diagram message starting at the " + ...
    interactions(1).RootFragment.Operands.Fragments(1).Name + ...
    " message end is of type " + ...
    string(interactions(1).RootFragment.Operands.Fragments(1).Message.Type) + ...
    " and the message label is " + ...
    interactions(1).RootFragment.Operands.Fragments(1).Message.Condition + ".")

The sequence diagram message starting at the switchout message end is of type Signal and the message label is rising(sw-1).

Use Iterator Utility to Step Through Sequence Diagram

Step through the Inhibit sequence diagram using the Iterator utility.

interaction = model.getInteraction('Inhibit');
interaction.open

Display the annotation from the interaction.

disp(interaction.Annotations.Content)

When inhibit is true, it means pedestrian crossing is not controlled by a walk signal on this intersection.

Use an iterator to navigate through all elements of a sequence diagram before extracting their properties.

iterator = systemcomposer.interaction.Iterator(interaction.RootFragment);
next = iterator.next;
while ~isempty(next)
    disp(class(next))
    next = iterator.next;
end

systemcomposer.interaction.RootFragment
systemcomposer.interaction.Operand
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.AltFragment
systemcomposer.interaction.Operand
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.Operand
systemcomposer.interaction.MessageEvent
systemcomposer.interaction.MessageEvent

More About

Definitions

Term	Definition	Application	More Information
sequence diagram	A sequence diagram represents the expected interaction between structural elements of an architecture as a sequence of message exchanges.	Use sequence diagrams to describe how the parts of a system interact.	Describe System Behavior Using Sequence Diagrams
lifeline	A lifeline is represented by a head and a timeline that proceeds down a vertical dotted line.	The head of a lifeline represents a component in an architecture model.	Add Lifelines and Messages
message	A message sends information from one lifeline to another. Messages are specified with a message label.	A message label has a trigger and a constraint. A trigger determines whether the message occurs. A constraint determines whether the message is valid.	Create Messages in Sequence Diagram
gate	A gate in a sequence diagram represents the root architecture of the corresponding architecture model.	Connect messages to gates to represent architecture ports.	Create Sequence Diagram Gates
annotation	An annotation describes the elements of a sequence diagram.	Use annotations to provide detailed explanations of elements or workflows captured by sequence diagrams.	Use Annotations to Describe Elements of Sequence Diagram
fragment	A fragment indicates how a group of messages specified within execute or interact.	A fragment is used to model complex sequences, such as alternatives, in a sequence diagram.	Author Sequence Diagram Fragments
operand	An operand is a region in a fragment. Fragments have one or more operands depending on the kind of fragment. Operands can contain messages and additional fragments.	Each operand can include a constraint to specify whether the messages inside the operand execute. You can express the precondition of an operand as a MATLAB Boolean expression using the input signal of a lifeline.	Add Fragments and Operands

Version History

Introduced in R2024a