Protocol specifications and component adaptors

In this article we examine the augmentation of application interfaces with enhanced specifications that include sequencing constraints called protocols. Protocols make explicit the relationship between messages (methods) supported by the application. These relationships are usually only given implicitly, either in the code or in textual comments. We define notions of interface compatibility based upon protocols and show how compatibility can be checked, discovering a class of errors that cannot be discovered via the type system alone. We then define software adaptors that can be used to bridge the difference between applications that have functionally compatible but type- and protocol-incompatible interfaces. We discuss what it means for an adaptor to be well formed. Leveraging the information provided by protocols, we show how adaptors can be automatically generated from a high-level description, called an interface mapping.