PCLOS: A Flexible Implementation of CLOS Persistence

We describe the design of a prototype which makes objects persistent. Our target language is the CommonLisp Object System (CLOS), although we pay attention to the eventual sharing of data with other languages. Our design is very flexible, in that it allows the simultaneous use of multiple, different databases. This is accomplished by defining a virtual database layer which consists of a core protocol that is expected to be implemented on all databases, and of protocol adapters which accommodate features offered by some databases, but not by others. This virtual database has been implemented for a simple, single-user, in-core data store, and for Iris, a multi-user, object-oriented database management system. We outline the advantages of the CLOS Metaclass Protocol for implementing object persistence or other low-level modifications to the CLOS implementation.