The Health Level Seven, Inc (HL7) is a standards development organization that produces standards for the exchange, integration, and management of clinical and administrative data in health care with an emphasis on interoperability of information systems . The HL7 YS standard is an object-oriented development methodology based on a RIM . HL7 YS also includes a number of other more specific information models as well as data types, vocabulary domains, and a messaging model.
The HL7 YS RIM is a static information model on which all other HL7 YS information models are based. It also provides the basis for the information content of all HL7 YS protocol standards. The RIM is expressed as
<xs:schema xmlns:xs="http:y/www.w3,org/200]/XMLScheraa" elementForm Defaults qualified" auributeFormDefault= unqualified'> <xs:eleniiMU name="Paiieni"> <xs:annotation>
<xs:documentation>Patient Demographics</xs:documentation> </3ts:annotation> <xs:complexType> <xs:all> <xs:elemem name="ID '> <xs:annoiation>
<xs:documentation>Paiieiu ID</xs:documentation> </xs:annotatinn> <xs:complexType /> </xs:element>
<xs:element name="Nanie"> <xs:annotation>
<xs:docunientation>PalieiU name</xs:documentation> </xs:annotation> </xs:element>
<xs:element name="Gender"> <xs:annotation>
<xs:docLimentatioii>Paiicm gendi;r</xs:documeiitaiion> </xs:annotation> <xs:complexType> <xs:chiiice> <xs:elemem name- Male /> <3ts:elemeiu name=' Female" /> </xs:choice> </xs:complexType> </xs:elemem> <xs:element name="DOB"> <xs:ani"ioiation>
<xs:documentationsPatienL dale of birth</xs:docunientaiion> </xs:annotation> </xs:element> </xs:all> <to:complexType> </xs:eleniL'i]l> </xs:schema>
Fig. 5. Instance document for the patient demographics XML schema depicted in Fig. 4
a UML class diagram. The core of the RIM is a metamodel that specifies the kinds of associations that may exist between the various classes in the other information models of HL7 V3. The HL7 RIM also includes the inheritance relationships for subclasses that are derived from the core classes. The structure of the RIM core classes is depicted Fig. 6.
The HL7 RIM specifies that an Entity may play a Role that has a Participation in an ^.ct. For example, a person entity may play a patient role that participates as the subject of a medication administration act. An Entity may also "scope" a Role being played by a given Entity in the sense of defining, guaranteeing, or acknowledging that the Role is played by the given Entity. A relationship between two acts (e.g., one act is a component of another act) is represented by an ActRelationship. A relationship between two roles (e.g., one role has direct authority over another role) is represented by a RoleLink.
The Entity class is used to represent a physical thing or an organization. For example, an Entity may be a living subject, a place, an organization, a material, a device, or a container. The Role class represents the competency or suitability of an Entity to play a given role while participating in appropriate acts. For example, a Role may be a patient, an employee, or equipment certified to perform specific functions. The Participation class represents the way that a Role participates in an Act, for example a performer, a subject, a witness, or a referrer. The Act class represents an intentional action. For example, an Act may be an observation, a procedure, a substance administration, or a patient encounter. An Act represented by this class may be in the process of occurring, have already occurred, or be intended or requested to occur. It may also simply be an act that could occur.
One of the strategies fostered by HL7 is to develop coherent, extensible standards that permit structured, encoded health care information of the type required to support patient care, to be exchanged between computer applications while preserving meaning. The RIM is an essential part of the HL7 V3 development methodology, as it provides an explicit representation of the semantic and lexical connections that exist between the information carried in the fields of HL7 messages. The HL7 Structured Documents Technical Committee (authors of the CDA - Clinical Document Architecture) and the Templates SIG of the Modeling and Methodology Technical Committee in HL7 are addressing the creation of standards for clinical documents  and templates . Without such standards, unstructured content is loosely communicated across an organization. In this framework, OSs can be seen as instances of structured documents containing tagged concepts and relationships between concepts.
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