This standard specifies the fundamental characteristics of the information model to be implemented by a specific architectural layer (i.e. the middleware) of the information system to provide a comprehensive and integrated storage of the common enterprise data and to support the fundamental business processes of the healthcare Organisation, as defined in part 1 of this standard “Health Informatics – Service Architecture - Part 1: Enterprise viewpoint”. The information model is specified without any –explicit or implicit- assumption on the physical technologies, tools or solutions to be adopted for its physical implementation in the various target scenarios. The specification is nevertheless formal, complete and non-ambiguous enough to allow implementers to derive an efficient design of the system in the specific technological environment that will be selected for the physical implementation. This specification does not aim at representing a fixed, complete, specification of all possible data that may be necessary for any requirement of any healthcare enterprise. It specifies only a set of characteristics –in terms of overall Organisation and individual information objects- identified as fundamental and common to all healthcare Organisations, and that shall be satisfied by the information model implemented by the middleware. Preserving the consistency with the provisions of this standard, physical implementations shall allow extensions to the standard information model in order to support additional and local requirements. Extensions shall include both the definition of additional attributes in the objects of the standard model, and the implementation of entirely new objects.