The Publish-Subscribe Pattern
4.2.2. The Publish-Subscribe Pattern With publish-subscribe messaging many senders can send messages to an entity on the server, often called a topic (e.g. in the JMS world). There can be many subscriptions on a topic, a subscription is just another word for a consumer of a topic. Each subscription receives a copy of each message sent to the topic. This differs from the message queue pattern where each message is only consumed by a single consumer. Subscriptions can optionally be durable which means they retain a copy of each message sent to the topic until the subscriber consumes them - even if the server crashes or is restarted in between. Non-durable subscriptions only last a maximum of the lifetime of the connection that created them. An example of publish-subscribe messaging would be a news feed. As news articles are created by different editors around the world they are sent to a news feed topic. There are many subscribers around the world who are interested in receiving news items - each one creates a subscription and the messaging system ensures that a copy of each news message is delivered to each subscription.