An activity stream is a publish-and-subscribe notification mechanism and conversation space typically found in social networking. It lists activities or events relevant to a person, group, topic or everything in the environment. A participant subscribes to, or “follows” entities (e.g., other participants or business application objects) to track their related activities. For example, a project management application may add status information, while a physical object connected to the Internet may report its state (e.g., tunnel lane closure).