This European standard provides guidance for the description, planning and development of new systems as well as for the integration of existing information systems, both within one enterprise and across different healthcare organisations through an architecture integrating the common data and business logic into a specific architectural layer (i.e. the middleware), distinct from individual applications and accessible throughout the whole information system through services, as shown in Figure 2 Figure 2The architectural principles are formalised according to the ISO/IEC 10746 (all parts) criteria and are therefore structured through the following three viewpoints:a)Enterprise viewpoint that specifies a set of fundamental common requirements at enterprise level with respect to the organisational purposes, scopes and policies that must be supported by the information and functionalities of the middleware. It also provides guidance on how one individual enterprise (e.g. a regional healthcare authority, a large hospital or any other where this model is applicable) may specify and document additional specific business requirements, with a view of achieving a complete specification, adequate for the characteristics of that enterprise. b)Information viewpoint that specifies the fundamental semantics of the information model to be implemented by the middleware to integrate the common enterprise data and to support the enterprise requirements formalised in the Enterprise viewpoint. It also provides guidance on how one individual enterprise may extend the standard model with additional concepts, needed to support local requirements in terms of information to be put in common.c)Computational viewpoint that specifies the scope and characteristics of the services that must be provided by the middleware for allowing the access to the common data as well as the execution of the business logic supporting the enterprise processes identified in the Information and Ent