Lingua-Franca: An IDL for Structural Subtyping Distributed Object Systems

Recently the trend has been towards applying object-oriented techniques to address problems of building scalable and maintainable distributed systems. Object-oriented programming increases modularity and data abstraction by supporting encapsulation through narrow, rigidly defined and strongly enforced interfaces to objects. Unfortunately, object-oriented interfaces and mechanisms are usually only accessible and enforced through language mechanisms or strict programming conventions. This severely limits the degree to which disjoint, unrelated components can interact in a multilingual, loosely coupled distributed system. An accepted solution to the language dependence problem is the use of high-level interface description languages (IDLs). IDLs provide a description mechanism for an object's interface that is independent of any programming language. In this paper we describe an interface description language and runtime support system that uses structural subtyping rules rather than the traditional interface name equivalence rules for conformance checking. We argue that the choice of structural subtyping rather than interface name equivalence leads to a less coupled and more extensible distributed system.