whats missing from the reuse picture for things like operating systems, compilers (somwhat), and databases is systems that use a 'lego' model of components that

whats missing from the reuse picture for things like operating systems, compilers (somwhat), and databases is systems that use a 'lego' model of components that can be put together into solutions rather than deployable systems (which can clearly be built on top). this provdies room for doing real customization without having to build all the things from ground zero, and is likely to be more robust than trying to attach functionality fully on the outside like was done here. in the database world it would be really nice to implement caching and sharding extensions inside the transactional envelope