Publish/Subscribe Interactions
Publish/subscribe interactions are driven by events (usually the arrival or creation of data)—a publisher makes information available for general distribution. Communication is in one direction (publisher to subscribers), and often one-to-many as shown in Event-Driven Publish/Subscribe Interaction. The complete interaction consists of one multicast message, published once, and received by all subscribers.
Figure 8: Event-Driven Publish/Subscribe Interaction
Example applications:
| • | Securities data feed handlers publish the latest stock prices to hundreds of traders on a trading floor simultaneously. |
| • | Materials movement systems distribute data to various materials handlers, controllers and tracking systems on a factory floor. |
| • | Inventory levels flow continuously to accounting, purchasing, marketing and other departments in a retail store. |
| • | A bug-tracking database immediately sends bug reports and updates to all personnel interested in a particular project. |
| • | A master database publishes updates to a set of internet mirrors. |
In publish/subscribe interactions, data producers are decoupled from data consumers—they do not coordinate data transmission with each other, except by using the same subject name. Producers publish data to the network at large.
Consumers place a standing request for data by subscribing. Consumers can listen for messages on any subject(s) on the network; a subscription is a request for messages.
Rendezvous software supports publish/subscribe interactions with multicast communication.