Artifact: Signal

Signal	An signal is an asynchronous event which may cause a state transition in the state machine of an object.
UML representation:	Class, stereotyped ½signal╗.
Worker:	Architect
Optionality:	Applicable to reactive (event-driven) systems or those which utilize asynchronous messaging.
More information:	Concepts: Events and Signals Concepts: Concurrency Checkpoints: Signal
Purpose Properties Timing Responsibility Tailoring

Input to Activities:

Capsule Design

Output from Activities:

Identify Design Elements

Purpose

A 'signal' is a kind of event that represents the specification of an asynchronous stimulus between two instances.

Properties

Property Name	Brief Description	UML Representation
Name	The name of the signal.	attribute
Brief Description	A brief description of the role and purpose of the signal.	Tagged value, of type "short text".
Responsibilities	The responsibilities defined by the class.	tagged value
Relationships	The generalizations in which the signal participates.	generalization relationship
Operations	The operations defined by the signal.	operation
Attributes	The attributes defined by the signal.	attributes

Timing

Some signals, specifically those representing the external events and the significant internal events to which the system must respond, are identified early in the elaboration phase. Other signals needed to communicate asynchronously within the system are identified in the latter part of the elaboration phase. All signals and events are architecturally significant and should be completely identified by the end of the elaboration phase.

Responsibility

The architect is responsible for all signals, ensuring that signals are being use appropriately.

Tailoring

Signals, a kind of event, are used to define mechanisms for asynchronous messaging. It is important for recipients of the signal to understand what the signal means, and for senders of the signal to use the signal properly.