A Basic Model of Typed Components

This paper studies specific language level abstractions for component-based programming. We propose a simple model which captures some basic ingredients — like explicit context dependence, dynamic binding and subtype polymorphism, late (dynamic) composition, and avoidance of inheritance in favor of object composition — that several authors have defended to be central to black-box object-oriented component programming styles. The model is expressed by a core imperative typed calculus, in which components are first-class entities, and whose basic constructs enable the composition, scripting, instantiation and definition of atomic components. Some motivating programming examples are presented, and the operational semantics is shown to enjoy a typesafety property. We also discuss an extension to the Java language aimed at supporting the proposed model, and some implementation issues.