Concept of HL7® RIM
The HL7® RIM concept was proposed in 1992 by ANSI/HISPP Joint Working Group for a Common Data Model. The first non-draft RIM (RIM 1.0) was published in Jan 2001. The HL7® RIM changed to ANSI “Continuous Maintenance Process” in January 2009. The Health Level 7® (HL7®) Reference Information Model (RIM) was once incepted as an object oriented information model to harmonize the definition of HL7® messages across different application domains. On the heels of the hugely successful HL7® version 2, version 3 and the RIM has received significant attention and credit.
The Health Level Seven® (HL7®) Reference Information Model (RIM) is a static model of health and health care information as viewed within the scope of HL7® standards development activities. It is the combined consensus view of information from the perspective of the HL7® working group and the HL7® international affiliates. The RIM is the ultimate source from which all HL7® version 3.0 protocol specification standards draw their information-related content.
The HL7® RIM provides a framework for the representation of the structures of and relationships between information that is independent of any particular technology or implementation environment. It is thus designed to support the work of database schema designers, software engineers and others by creating a single environment for messaging which can be shared by all healthcare institutions.
The RIM defines a set pre-defined Attributes for each class and these are the only ones allowed in HL7® messages. Each attribute has a specified Data Type. These Attributes and Data Types become tags in HL7® XML messages. Message specifications, to do a particular task, use a sub-set of the available RIM Attributes, listing each element used and how many repeats are allowed. This is known as refinement. Each Data Type is constrained to the simplest structure that meets the requirements of the task. HL7® V3 uses a graphical representation, called Refined Message Information Model (RMIM) to display the structure of a message as a colour-coded diagram. Most RMIMs can be shown on a single sheet of paper or PowerPoint slide and these RMIM diagrams are used to design messages and to illustrate what each HL7® message consists. The actual interchange (the wire format) is usually XML.
All of the XML tags and attributes used in V3 messages are derived from the HL7® Reference Information Model (RIM) and the HL7® V3 Data Types. The structure of each HL7® message is set out in an XML schema, which specifies which tags and attributes are needed or allowed in the message, their order and the number of times each may occur, together with annotations describing how each tag shall be used.
According to the information model conception, the RIM, and the HL7® messages defined in its terms, are about objects in information systems – hereafter called ‘Objects’ – which ‘represent’ things and processes in reality. Consider an example, a human being named ‘John Smith’ is represented by an Object containing John Smith’s demographic or medical data. This Object is different from John Smith himself.
The Health Level Seven (HL7®) Reference Information Model (RIM) is a static model of health and health care information as viewed within the scope of HL7® standards development activities. It is the combined consensus view of information from the perspective of the HL7® working group and the HL7® international affiliates. The RIM is the ultimate source from which all HL7® version 3.0 protocol specification standards draw their informationrelated content.
The classes, attributes, statemachines, and relationships in the RIM are used to derive domain specific information models that are then transformed through a series of constraining refinement processes to eventually yield a static model of the information content of an HL7 standard. The HL7® V3 standard development process defines the rules
governing the derivation of domain information models from the RIM and the refinement of those models into HL7 standard specifications. The rules require that all information structures in derived models be traceable back to the RIM and that their semantic and related business rules not conflict with those specified in the RIM.
The RIM is only one model of healthcare information needs. The abstract style of the RIM and the ability to extend the RIM through vocabulary specifications make the RIM applicable to any conceivable healthcare system information interchange scenario. Furth it is conceptually applicable to any information domain involving entities playing roles and participating in acts.The universal applicability of the RIM makes it particularly useful for an organization like HL7® that has to consider the needs of a large and diverse membership. The style of the RIM makes it extremely stable, which is another important characteristic for HL7®.
The HL7 standards development process calls for the creation of domain specific models derived from the RIM and the incremental refinement of those models into design models that are specific to the problem area. These problem area specific design models narrow the abstractness of the RIM and include constraints on attribute values and class relationships that are use case specific. External organizations considering using the HL7 RIM are advised to adopt a similar process of deriving design models as a transformation of the RIM.
The V3 RIM is based on a simple back bone structure and consists of three main classes, Act, Role and Entity, linked together using three association classes such as act Relationship, Participation and Role Link.
In HL7 V3, every happening is an Act, which is analogous to a verb in English. Each act may have any number of Participations, which are Roles, played by entities. These are analogous to nouns. Each act may also be related to other Acts through act Relationships. Act, Role and Entity classes have a number of specializations.
Consider an example entity has a specialization called Living Subject, which itself has a specialisation called Person. Person inherits the attributes of both Entity and Living Subject.
Structural Attributes are a device, which is used to reduce the size of the original RIM from over 100 classes to a simple backbone of six main classes. Structural attributes are used to specify what each RIM class means when used in a message.
For example, every Act has a class code and a mood code. The class code states what sort of Act this is, such as observation, encounter, or administration of a drug. The primary use of structural attributes is in the design of messages or other services, which are then implemented in computer applications.
Each of the main backbone classes (Act, Role and Entity) has a number other classes linked to through a line with an open triangle arrowhead at the backbone class end. This is the UML symbol for specialisation. The class that is pointing is a specialisation of the class that is being pointed towards which is a generalization. The specialization inherits all of the properties of the generalization, by adding any specific attributes of its own.
For example, the class Patient, at the top centre of the RIM, is a specialisation of Role with the addition of the optional attribute veryImportantPersonCode. The convention is that only a class, which has one or more additional attributes specific to itself, is shown on the RIM. A number of frequently used attributes are found in more than one class. These include: id, code, and status code.