Database Cooperation: Classification and Middleware Tools

We propose new criteria for the classi cation of systems for database cooperation, based on the nature of the component databases. In fact, the traditional criteria | heterogeneity, distribution, and autonomy| are often constraints for the design process, rather than design parameters. In this case, other features of the component databases should be addressed. We claim that a more useful classi cation can be based on three new criteria: (a) degree of transparency, (b) complexity of operations, and (c) level of liveliness of data. This leads us to distinguish three main categories of systems: (i) multidatabases, (ii) data warehouses, (iii) local information systems with external data. For each of these categories we discuss implementations based on tools o ered by currently available technology.