Types for Active Objects Based on Trace Semantics

                          Franz Puntigam
    Institut für Computersprachen, Technische Universität Wien
           Argentinierstraße 8, A-1040 Vienna, Austria
             E-mail: franz@complang.tuwien.ac.at

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