Publish/subscribe in perspective

The importance of flexible, well-structured, but especially scalable communication mechanisms has been drastically increasing in the last decade. Applications tend to become very dynamic, i.e., components are not always up and are not locality-bound. These constraints visualize the demand for more flexible communication models, reflecting the nature of tomorrows applications. The publish/subscribe interaction style has proven its ability to fill this gap. Based on the concept of information bus [OPSS93], publish/subscribe promotes the decoupling of parties in time as well as space : consumers subscribe to the information bus by specifiying the nature of the information they are interested in, and producers publish information on that bus.

The classical topic-based or subject-based publish/subscribe style involves a classification of the information by introducing group-like notions [Pow96], and is incorporated by most industrial strength solutions, e.g., [Cor99,TIB99,Ske98,AEM99]. Topics are however static and allow only a limited expressiveness [Car98]. More recently, research efforts have been targeted towards content-based (property-based  [RW97]) publish/subscribe schemes [Car98,SA97,BCM+99]. This more flexible variant removes entirely the ``arbitrary'' division of the information space, and lets consumers delineate their individual interests by expressing properties of messages they wish to receive.