A META-LEVEL ARCHITECTURE FOR PROTOTYPING OBJECT SYSTEMS
Jeff McAffer · 1995
As applications become larger and more complex, it is frequently the case that system components require varying models of computation. The use of different computational models is not well supported by standard object-oriented mechanisms and systems. Typical mechanisms implicitly encapsulate meta-level (i.e., computational) semantics along with the base-level (i.e., domain) behaviour. Objects defined using one model cannot easily be executed under another and so cannot be reused. A major problem is the inclusion of base-level language constructs in the meta-level architecture design. Meta-levels typically only facilitate concepts which are similar to those in the original base-level language and so cannot describe widely differing models of execution. We present a meta-level architecture founded on the novel principle of fine-grained, operational decomposition of the meta-level into objects. Unlike others, our approach bases the design of the architecture on the operations which occur during object execution (e.g., send, lookup) rather than the structural nature of an object’s representation (e.g., class, method). This clearly separates the elements of the meta-level from those of the base-level language and so opens the meta-level to more radical change. The power of this approach is shown via several markedly different object