Topic-based messaging. In a publish-subscribe system, senders label each message with the name of a topic ("publish"), rather than addressing it to specific recipients. The messaging system then sends the message to all eligible systems that have asked to receive messages on that topic ("subscribe"). This form of asynchronous messaging is a far more scalable architecture than point-to-point alternatives such as message queuing, since message senders need only concern themselves with creating the original message, and can leave the task of servicing recipients to the messaging infrastructure. It is a very loosely coupled architecture, in which senders often do not even know who their subscribers are.