Service integration has the following types of bus destinations each with a different purpose: queue, topic space, foreign, and alias.
A service integration topic space destination is not localized in a particular bus member. Service integration maintains a list of subscriptions in the topic space and matches each publication against that list. When a new publication matches one or more subscriptions in the topic space, service integration delivers a copy of the publication to each subscriber. If necessary, service integration can queue the publication message until the subscriber is ready to receive it. If the new publication does not match any subscription, service integration discards the publication.
The foreign bus can be another service integration bus or a WebSphere MQ network (that is, one or more interconnected WebSphere MQ queue managers or queue-sharing groups). When a producer sends a message to a foreign destination, service integration delivers the message to the foreign bus. The foreign bus is then responsible for queueing the message, as appropriate, based on its definition of the destination.
To override messaging defaults of a destination on a foreign bus, you configure the properties (for example, the default priority) of the foreign destination. To override security settings and control which users and groups in the local bus have access to a destination in a foreign bus, you configure the destination roles of the foreign destination. These properties apply when an application that is connected to the local bus sends messages to the destination in the foreign bus.
You do not use foreign destinations for publish-subscribe messaging. Instead, applications publish messages locally by using a topic space destination in the local bus, and you configure a service integration bus link or a WebSphere MQ link. These links propagate the published messages into the foreign bus, or buses, where subscribers receive the messages. For a link to a service integration bus, configure topic space mappings, as described in Configuring topic space mappings between service integration buses. For a link to a WebSphere MQ network, configure a publish/subscribe bridge, as described in Publish/subscribe messaging through a WebSphere MQ link.
When you use an alias destination, you can also set properties (for example, the default quality of service) for the alias destination. When an application uses the alias destination, these properties override the properties of the target destination. If you do not want to override a property, configure the alias destination to inherit the corresponding property from the target destination.
When you use an alias destination, you can also configure destination roles for the alias destination. When the application uses the alias destination, service integration in the local bus uses these roles to control which users and groups in the local bus have access to the target destination. If you do not want to override the security for the target destination, configure the alias destination to delegate the authorization check to the target destination.
Bus destinations can be either permanent or temporary. When an administrator configures a service integration destination, that destination is a permanent destination that exists until an administrator explicitly deletes it. In contrast, a temporary destination exists only while an application is using it. Typically, this situation occurs when the application uses a JMS temporary destination. Service integration creates a corresponding temporary service integration bus destination.
You can configure queue, topic space, and alias destinations with one or more mediations. Mediations are programs that process each message after the producing application sends the message to the destination, and before any consuming applications receive the message from the destination. For example, a mediation can modify the actual message, or redirect the message to another destination or sequence of destinations, or both.