Types for Active Objects Based on Trace Semantics

Static typing and subtyping are useful for the support of incremental refinement and reuse in object-oriented languages. Although demanded, there is currently no appropriate type model for concurrent object-oriented languages that supports dynamic behavior modifications. We propose a type model based on a process calculus with trace semantics and demonstrate its use in a simple language. This model is an extension of conventional models for types and subtyping and ensures that all messages are processed even if object behavior is modified dynamically. Keywords type model, subtyping, concurrency, process algebra 1 INTRODUCTION The object-oriented paradigm is now probably the most important paradigm for the development of software. Object-oriented programming languages are based on objects communicating with other objects by exchanging messages (Wegner, 1990). An object is a self-contained entity characterized by its identity, state and behavior. The objects are classified according to..