(Most recent version: "A Behavioral Type System and Its Application in Ptolemy II," to appear in Formal Aspects of Computing Journal, special issue on "Semantic Foundations of Engineering Design Languages.")

Behavioral Types for Component-Based Design

Edward A. Lee and Yuhong Xiong

Memorandum UCB/ERL M02/29,
EECS, University of California, Berkeley, CA 94720, USA
September 27, 2002

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ABSTRACT

We present a framework to extend the concept of type systems in programming languages to capture the dynamic interaction in component-based design, including the communication protocols between components. Our system is based on a light-weight formalism - interface automata. We first propose some extensions to the theory of interface automata to make them more powerful, then use the extended theory to establish a behavioral-level type system. In our system, the interaction types and the dynamic behavior of components are defined using interface automata, and type checking, which checks the compatibility of a component with a certain interaction type, is conducted through automata composition. Our type system is polymorphic in that a component may be compatible with more than one interaction type. We show that a subtyping relation exists among various interaction types and that this relation can be described using a partial order. This behavioral type order can be used to facilitate the design of polymorphic components and simplify type checking. In addition to static type checking, we also propose to extend the use of interface automata to the on-line reflection of component states and to run-time type checking. We illustrate our framework using a component-based design environment, Ptolemy II, and discuss the trade-offs in the design of behavioral type systems.