This section describes the database objects that specify the basic design of an application that uses Service Broker.
At design time, Service Broker applications specify the following objects:
- Message types — Define the names of the messages exchanged between applications. Optionally provide validation for the messages.
- Contracts— Specify the direction and type of messages in a given conversation.
- Queues— Store messages. This storage mechanism allows for asynchronous communication between services. Service Broker queues provide additional benefits, such as automatically locking messages in the same conversation group.
- Services— Are addressable endpoints for conversations. Service Broker messages are sent from one service to another service. A service specifies a queue to hold messages, and specifies the contracts for which the service can be the target. A contract provides a service with a well-defined set of message types.
A Service Broker application uses the SQL Server objects in the previous list to conduct a conversation. Any program that can run Transact-SQL statements in SQL Server can use Service Broker. Applications can be stored procedures written in Transact-SQL or a CLR-compliant language, or they can be external programs that connect to an instance of SQL Server.
The following diagram shows a Service Broker service:
As shown in the illustration, the ProcessExpenses contract specifies three message types: SubmitExpense, AcceptDenyExpense, and ReimbursementIssued. The contract lists the message types required for a conversation that performs an expense reimbursement task. The ProcessExpenses contract governs all conversations between the ProcessExpense service and any services that initiate a conversation with the ProcessExpense service. The ProcessExpense service stores incoming and outgoing messages in the ExpenseQueue queue. The ExpenseProcessing stored procedure receives messages from this queue, processes the messages, and sends messages back to the queue for routing to the appropriate broker if a reply is necessary.