Arnd Poetzsch-Heffter (FernUniv. Hagen)

Towards Type Systems for Dynamic Components
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In an object-oriented setting, a system is a collection of
communicating objects. Current programming techniques do not support
mechanisms to structure such collections, e.g. by providing constructs
to group objects and to enforce interfaces of such groups. In the
following, we call a group of objects that work closely together a
{\em (dynamic) component}. We assume that two components are either
disjoint w.r.t. the objects they contain or that one component is part
of the other component, i.e. all objects of the former component
belong as well to the latter. Consequently, components induce a
hierarchical structure on the objects in a system.

The component structure introduces a boundary between objects inside
and outside the component. In particular, given a component C, we can
distinguish four kinds of objects:

 - internal: objects in C that must not be referenced from 
   the outside;
 - interface: objects in C that may be referenced from the 
   outside are called interface objects;
 - used: objects outside C that are referenced from objects in
   C are called used objects;
 - external: objects not directly referenced from objects in C.

All the communication of a component with the outside objects can be
controlled by the interface and used objects. The types of the
interface objects describe what kind of services the component
provides; as in all typed OO-languages, the types determine which
methods can be invoked on interface objects, i.e. from the outside.
The types of the used objects explain what kind of service