Content-Based Publish/Subscribe with Structural Reflection

This paper presents a pragmatic way of implementing content-based publish/subscribe in a strongly typed object-oriented language. In short, we use structural reflection to implement filter objects through which applications express their subscription patterns. Our approach is pragmatic in the sense that it alleviates the need for any specific subscription language. It preserves encapsulation of message objects and helps avoiding errors. We illustrate our approach in the context of Distributed Asynchronous Collections (DACs), programming abstractions for message-oriented interaction. DACs are implemented in Java, whose inherent reflective capabilities fully satisfy the requirements of our content-based subscription scheme. Our approach is however not limited to the context of DACs, but could be put to work easily in other existing event-based systems.