templates) will ultimately just be instances of the standard content definitions. This provides a basis for standardised querying to work. Without the archetype "library" level, every data set (i.e. chunk of operational content) is uniquely defined and a standard approach to querying is difficult. Accordingly, openEHR defines a method of querying based on archetypes, known as AQL (Archetype Querying Language). Notably, openEHR has been used to model shared care plan. The archetypes have been designed to accommodate the concepts of the shared care plan. While individual health records may be vastly different in content, the core information in openEHR data instances always complies to archetypes. The way this works is by creating archetypes which express clinical information in a way that is highly reusable, even universal in some cases. Archetype formalism openEHR archetypes are expressed in "Archetype Definition Language", an openEHR public specification. Two versions are available: ADL 1.4, and ADL 2, a new release with better support for specialisation, redefinition and annotations, among other improvements. The 1.4 release of ADL and its "object model" counterpart Archetype Object Model (AOM) are the basis for the CEN and ISO "Archetype Definition Language" standard (ISO standard 13606-2). Templates have historically been developed in a simple, de facto industry-developed XML format, known as ".oet", after the file extension. ADL 2 defines a way to express templates seamlessly with archetypes, using extensions of the ADL language. Quality assurance of archetypes Various principles for developing archetypes have been identified. For example, a set of openEHR archetypes needs to be quality managed to conform to a number of axioms such as being mutually exclusive. The archetypes can be managed independently from software implementations and infrastructure, in the hands of clinician groups to ensure they meet the real needs on the ground. Archetypes are designed to allow the specification of clinical knowledge to evolve and develop over time. Challenges in implementation of information designs expressed in openEHR centre on the extent to which actual system constraints are in harmony with the information design. In the field of Electronic health records there are a number of existing information models with overlaps in their scope which are difficult to manage, such as between HL7 V3 and SNOMED CT. The openEHR approach faces harmonisation challenges unless used in isolation. International collaboration Following the openEHR approach, the use of shared and governed archetypes globally would ensure openEHR health data could be