The integration of legacy systems represents one of the most urgent priorities of healthcare information systems in order to allow the whole information system to meet the evolving clinical organisational and managerial needs of the healthcare organisation. This paper discusses how the introduction of a middleware of common services providing functionalities addressing specific needs of the healthcare business domain reduces the effort necessary for allowing existing systems to interwork, and automatically establishes a functional and information basis common to the whole organisation, on top of which also new applications can be rapidly developed, natively integrated with the rest of the system.

An actual implementation of the architectural structure described in this paper has been developed during the EDITH/Italy project, carried out in 1992-1994 by a group of hospitals and industries with the contribution of the European Union under the Esprit programme. Through this initiative the DHE^® middleware and a set of applications already operational in the live environment has been developed.

This approach is also the basis of the HANSA project, presently running under the Telematics Application Programme, with the objective of installing and demonstrating the DHE middleware in approximately 20 hospitals from nine European countries, as a common platform for a migration strategy for evolving and opening existing systems.