Editing Publish–subscribe pattern (section)

{{Short description|Messaging pattern in which senders and receivers do not directly communicate}}
{{About||the Macintosh feature introduced with System 7|Publish and Subscribe (Mac OS)|the practice of paying before a work is complete|Subscription business model}}
{{redirect|PubSub|the defunct search website|PubSub (website)}}
{{redirect|Pub sub|the sandwich sold at Publix|Publix#Stores}}

{{More citations needed|date=March 2010}}

In [[software architecture]], '''publish–subscribe''' or '''pub/sub''' is a [[messaging pattern]] where publishers categorize [[message passing|messages]] into classes that are received by subscribers. This is contrasted to the typical messaging pattern model where publishers send messages directly to subscribers.

Similarly, subscribers express interest in one or more classes and only receive messages that are of interest, without knowledge of which publishers, if any, there are.

Publish–subscribe is a sibling of the [[message queue]] paradigm, and is typically one part of a larger [[message-oriented middleware]] system. Most messaging systems support both the pub/sub and message queue models in their [[application programming interface|API]]; e.g., [[Java Message Service]] (JMS).

This pattern provides greater network [[scalability]] and a more dynamic [[network topology]], with a resulting decreased flexibility to modify the publisher and the structure of the published data. According to Gregor Hohpe, compared with synchronous messaging patterns (such as [[Remote procedure call|RPC]]) and [[Point-to-point (telecommunications)|point-to-point messaging]] patterns, publish–subscribe provides the highest level of [[Loose coupling|decoupling]] among architectural components, however it can also [[Coupling (computer programming)|couple]] them in some other ways (such as format and semantic coupling) so they become messy over time. <ref>{{Cite book |last=Hohpe |first=Gregor |title=Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions |publisher=Addison-Wesley Professional |year=2003 |isbn=978-0321200686}}</ref>