A stateful and open publish-subscribe structure for online marketplaces

We observe a mismatch between how academia models publish-subscribe systems for marketplace applications and how such applications are actually structured by the industry. To address this mismatch, we propose a new structure for online marketplace applications. A stateful and open publish-subscribe system exposes internal state and events to clients, through both a search mechanism and a subscription mechanism. This way, sellers and buyers may get valuable insight into the activity of the participants of the marketplace. Admittedly, this contradicts the idea that publishers and subscribers should be strictly decoupled. However, we argue that at a high level of abstraction this decoupling is unnecessary, or even unwanted, for many marketplace applications. Additionally, the structure presents the new idea of recursive subscriptions, and argues for its applicability in marketplace applications.