In contrast to traditional group communication systems, publish/subscribe systems focus on scalability and to that end sacrifice strong semantics. Membership is typically one aspect of publish/subscribe systems that is associated with weak semantics because view control mechanisms can easily become a bottleneck with increasing numbers of participants, especially as these join and leave frequently. Anonymity among participants in publish/subscribe communication is viewed as one of the main contributors to scalability next to asynchrony. While some applications may indeed not need information on participating entities, many current and future applications rely on information on their client population.

In this project, we are working on lightweight support for gathering aggregation information (e.g., client population) in content-based publish/subscribe systems. However, it does not focus on a specific kind of aggregation. Instead, it generalizes at the infrastructure level: each application can request its own specific type of aggregation information.

This work is based on an international cooperation between TU Darmstadt (Germany), Purdue University (USA), Imperial College London (UK), University of Otago (New Zealand) and Vrije Universiteit Amsterdam (Netherlands).