In messaging systems, message routing is done on the basis of a concept called topics. When a particular user wants to publish a message to a particular sector, he creates a topic typically with a name relevant to the messages to be published. For example, to publish messages related to sports, a topic by the name 'SportsNews' can be created and messages related to sports news can be published under that topic.
Users can look up the different topics in the topic tree, subscribe to selected topics and receive messages which are published to that topic by the publishers. According to the example above, a user is interested on sports can subscribed to the topic 'SportsNews'. This way the user can continue to receive messages published to that topic.
The message publish and subscribe flow of topics is depicted in the diagram below.
Figure: Message Publish-Subscribe Flow of Topics
The topics and subscriptions management capability in WSO2 Message Broker is provided by the following feature in the WSO2 feature repository.
Name : WSO2 Carbon - Event Feature
Identifier : org.wso2.carbon.event.feature.group
Name : WSO2 Carbon - Feature - Andes
Identifier : org.wso2.carbon.andes.feature.group
This feature can be removed or added to a different distribution if it is not already bundled with it using the instructions given in section, Working with Features.