International standards play a vital role in the realisation of interoperability amongst components of healthcare systems, both on a national and international level. We regard the development and application of the electronic health record as a key area for standardization. The primary goal of the EHR is to support continuity of care by providing a complete history of the patient with topical summarizations, based on ongoing secondary processing of the raw data by intelligent software applications linked to ontologies expressing the most updated medical knowledge, as well as the specifications of all recognized data standards. The EHR thus comprises a set of health related data and information about a patient stored in an electronic form. These not only include re-imbursement information, measurements, and text but also all other electronic data related to a patient such as laboratory test results, images, diagnosis, audio files, films or 3-dimensional anatomic models.

The standardisation of the representation of all these data and their exchange amongst different domain specific systems is a wide field covered by many diverse organisations, governmental and non-governmental institutions and working groups. Accordingly, there are as many different standardisation efforts on the way, which partly converge, and partly go into completely opposite directions. We extensively describe the most important standards development organisations (SDOs) and initiatives in "RIDE D.2.2.1-Standardization efforts for providing semantic interoperability in the eHealth domain". However, if we consider the great number of standardization initiatives and the rapid speed of scientific development as given, we believe that conformance to standards or implementation of them will not solve the basic problems of interoperability. The U.S. National Alliance for Health Information Technology (NAHIT) maintains a Directory of eHealth Standards. So far (26 April 2006) the NAHIT Directory enumerates 2104 standards related to ICT in healthcare, produced by 436 separate organisations. There are 34 organisations which issued 191 standards specific to EHRs alone. Thus, we have to assume that there will always be some health care institutions that decide to use different incompatible EHR standards.

At present, it seems highly unrealistic to expect all healthcare institutions and service providers to agree on a single universal standard. It is not surprising that the active standard development organizations in healthcare have not agreed upon a common standard for EHRs. In the USA, the Health Level Seven (HL7) SDO has released a specification for medical record messages, which basically relays a clinical document to the medical records unit of the healthcare system. The clinical document format is defined in a new standard created by HL7 called the Clinical Document Architecture (CDA). A collection of medical CDA documents might serve as a good foundation for an EHR. Unfortunately, this prospect is beyond the scope of the currently available HL7 specifications. Redundancy, lack of coherency and unmanageable complexity in such an aggregation pose serious obstacles for the realisation of such an approach. In Europe on the other hand, SDOs, such as the European standardization institute Comite Europeen de Normalisation (CEN), view an EHR as a standardized information entity to which health care professionals should enter the data directly during attested transactions. Such an opposed approach to the document-centric approach taken by HL7 can be found in a few pre-standard specifications, such as prENV 13606 by TC-251 of CEN.

Medical information systems store medical information in a structured, normalized database in which each basic unit of information is kept separately. Thus, the semantics of each individual entry in the patient record is retained. Nevertheless, medical information systems still allow to combine such entries into a classical document which is designed to be exchanged in digital form between different systems, for example by using HL7 messages or in the printed form, and this is where ambiguities originate. For HL7 CDA, DICOM SR and MML, the persistent document is the basic unit in which information is assembled, stored and communicated, whereas in EHRcom, communication is based on the "EHR extract", which is not equivalent to a document in this sense as it comprises one or more compositions (which are roughly equivalent to documents) in conjunction with structuring information such as folders. It is such a composition which is analogous to a document.