A Message Queuing trigger is an automated mechanism for implementing an action in response to a message arriving at a specific monitored queue on the local computer. Each trigger is comprised of a set of one or more rules, with each rule containing one or more conditions that can be tested and an action to take when all the conditions are evaluated as true.
A rule is a conditions-action pair. Each rule describes a set of one or more conditions, which can be evaluated as true or false, and specifies an action in the form of a COM component or executable file that can be invoked when all the conditions associated with the rule are evaluated as true.
A condition is a test that is applied to a message when the message arrives at the monitored queue. Conditions can test only the properties of the message. Each condition is expressed as a logical statement that can be evaluated as true or false, and a rule may have more than one condition. For example, a single rule may have conditions that test both the label and priority properties of a message.
An action is an executable behavior that is invoked when its associated conditions are evaluated as true. The action can be defined by a COM component and parameters or by an executable file and parameters (or command-line arguments). The parameters can be specific message properties, the trigger's name or identifier, a string literal, or a numeric literal.
For information on the supported parameters, see the Message Queuing online Help provided with Windows® XP Professional or operating systems from the Windows Server 2003 family.
The following illustration shows the relationships between queues, triggers, and rules.
|There can be a one-to-many relationship between queues and triggers, between triggers and rules, and between rules and conditions, but there is a one-to-one relationship between rules and their conditions-action pair. The conditions-action pair of each rule is what defines the business rule for the trigger.|
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The two types of triggers supported by the Message Queuing Triggers service
How the Message Queuing Triggers service reads messages
How to create and manage trigger components