Lightweight Morphing Support for Evolving Middleware Data Exchanges in Distributed Applications

Most systems must evolve as their missions or roles change and/or as they adapt to new execution environments. When evolving large distributed applications, it is particularly difficult to make changes to the data formats that underlie their components' communications, because such 'format evolution' can affect all or many application components. Prior approaches to the problem of implementing changes in the communications of a deployed system have relied upon ad-hoc solutions or on protocol negotiation to avoid message format mismatches. Unfortunately, such solutions tend to increase the complexity of application code. This paper presents a novel approach to the problem of data format evolution that combines meta-data about the data being exchanged with dynamic binary code generation to create a robust data exchange system that naturally supports application evolution. The idea is to specialize the communications of application components by dynamically generating the code that can automatically transform incoming data into forms that receiving components can understand. A realistic example in the context of publish/subscribe middleware is used to illustrate how this technique can be applied to enhance interoperability between different version of distributed applications