Figure below shows the methodology used in HL7V3.0
The different processes in the HL7V3.0 methodology to obtain the message specifications are described below
Use Case Modeling:
Ø Scope statement: A high level use case for the entire project
Ø Use case: Describes specific situations in which communication between healthcare entities is needed
Ø Actor: An entity which initiates or participates in the use case. Discovered in the process of developing use cases
Ø Use Case Diagram: Provides a graphical form to develop the use case model from the business process analysis and makes it easy to show the relationship between use cases
The Interaction Model
Ø Describes roles to which systems may claim conformance
Ø Fine-grained abstraction; every system will claim several roles
Ø Not standardizing system or application functions, only messaging roles
Ø Basis for contractual agreement
Ø Potential basis for conformance testing
Ø Captured in a MODEL, a TABLE, and a DIAGRAM
Each Interaction consists of:
Ø Trigger event :Event dependency usually expressed as the state of one or more classes
Ø Message ID : Each interaction sends one particular message
Ø Sender role
Ø Receiver role
Ø Receiver responsibility :A specific functional responsibility for the receiver to initiate another (consequential) interaction
The information model consists of the following
Ø A detailed and precise definition for the information from which the data content of HL7 messages are drawn.
Ø Follows object-oriented modeling and diagramming techniques, and is centered on a depiction of the classes that form the basis for the objects in HL7 messages.
Ø Provides a means for expressing and reconciling differences in data definition independent of message structure.
Ø Forms a shared view of the information domain used across all HL7 messages.
The Information Model defines
Ø classes, attributes, data types, and relationships
Ø vocabulary domains, code systems, and value sets
Ø states, trigger events, and transitions
Reference Information Model:
RIM is conveniently fashioned into three areas – semantic control, structured documents and message control.
The backbone of RIM consists of four primary classes and two linking classes. The four primary classes in the semantic content partition of the RIM are
Act: An Act is defined as intentional healthcare related action in the business domain of HL7. An instance is a record of an act. Acts definitions (master files), orders, plans, and performance records (events) are all represented by an instance of Act. An act is represented by a brick colored block in the RIM as following example
Act has the following sub-classes
Entity: Entity is a physical thing or organization and grouping of physical things. A physical thing is anything that has extent in space, mass. Excludes information structures, electronic medical records, messages, data structures, etc. An Entity is represented by a green colored block in the RIM as following example
Entity has the following sub-classes
Role has the following sub-classes:
Participation: Role exists only within the scope of one act. Acts have multiple participants, each of which is an entity in a role. Role signifies competence while participation signifies performance. Participation is represented in the RIM by the following block
Participation has ManagedParticipation sub-class.
Act Relationship: ActRelationship is association between a source Act and a target Act. A point from a later instance to a earlier instance OR point from collector instance to component instance.Act Relationship is represented in RIM by the following block
ActRelationship has no sub-classes
Role Link: Role Link is a relationship between two entity roles. For example Clinicians relationship with a Hospital and a Patients relationship with a Hospital to express the doctor and patient relationship. Role Link is represented in RIM by the following block
RIM Classes Example
Figure below shows the relationships between the different classes in the RIM with an example
In the above example the Act Examination is performed by Entity Person A in his role as GP and the Subject of the Examination is the Entity Person B in his role as Patient.
Class attributes are the core components of the information model. The attributes are the source for all the information content of HL7. There are three special kinds of attributes in the information model: identifier attributes, classifier attributes and state attributes.
Ø Identifier attributes: Identifier attributes can be used to identify an instance of a class. Values of identifier attributes never change. Examples of identifier attributes from the RIM include Entity.id and Act.id, which uniquely identify a particular Entity or Act respectively
Ø Classifier Attributes: The classifier attributes are a critical aspect of the classes forming the backbone of the RIM. The classifier attributes are named “classCode”.
Ø Structural Attributes: Structural attributes are those attributes whose coded values are needed to fully interpret the classes that they classify. ClassCode together with moodCode, typeCode and determinerCode are the structural attributes.
Ø State Attributes: A state attribute is used in subject classes (classes that a Technical Committee designates as the central focus of a collection of messages). It contains a value that concisely indicates the current state (named condition) of the class.
The Message Design in HL7V3 from RIM is obtained as follows Message Design Overview
Domain Message Information Model:
Ø Full description (model) of the information classes within a domain and the way in which they are being used
Ø Classes are ‘cloned’ (copied and adapted) and renamed (alias) according to the way they are used in the domain context
Ø Data Types and vocabulary for attributes are specified
Ø Every RIM class category has its own colour; this makes the model description more visual
To obtain D-MIM from RIM
Ø Select RIM classes to be included in D-MIM Select the subset of RIM classes relevant to the problem domain.
Ø Clone subset classes of the RIM If the same RIM class is selected to meet different information needs then create as many clones of the RIM base class as needed. Ø Select a subset of class relationships Add relationships between the D-MIM clones consistent with existing class relationships in the RIM.
Ø Select a subset of class attributes For each D-MIM clone select the applicable attributes from its RIM base class.
Ø Select a subset of attribute data types and vocabulary domains Assign data types and domains to D-MIM attributes that are consistent with assigned data types and domains in the RIM
Refined Message Information Model:
Ø Same type of representation as D-MIM
Ø Aimed for a specific category of interaction (e.g. all inpatient admission related messages) Ø Special form of an R-MIM are the Common Message Element Types (CMETs).These express common and reusable ‘information units’, that are derived from a D-MIM (like all R-MIMs) but can be used in other D-MIMs (and therefore R-MIMs) as building blocks (e.g. ‘patient’)
To obtain R-MIM from D-MIM
Ø Create clones of D-MIM classes and attributes Further specialize D-MIM classes by creating additional clones for each unique collection of attributes
Ø Assign alias class and relationship role names Assign domain specific names to class clones Ø Eliminate unnecessary class hierarchies Remove classes with no attributes and relationships from the class hierarchy
Ø Finalize class relationships and cardinality Alter relationship cardinality to reflect the appropriate minimum and maximum class occurrences
Ø Finalize attribute data types and domains Replace data type and domain specifications with the most appropriate constrained version of each
Hierarchical Message Definition
HMD is a further restriction of an R-MIM:sequentialized/serialized; represented in a different format. To create a HMD
Ø Select a root class for the message Chose a class to serve as the starting point for message content
Ø Arrange classes and attributes hierarchically Follow the relationships from class to class and add the attributes to the HMD.
Ø Declare inclusion and repetition constraints For each attribute specify if its presence in message content is optional, mandatory, or conditional and specify the number of times the attribute may repeat
Ø Declare data type and domain value constraints Declare additional constraints on the data types and domain values
Ø Assign message element names Assign a final meaningful business name to each attribute in the HMDHL7 V3.0 Data Types:
HL7 data types define the structure and constrain the allowable values of attributes in the RIM. The HL7 data type specification declares the set of data types, identifies components of complex types, and defines relationships between data types. The HL7 data type implementation technology specification defines constraints and operations for data types and describes how data types are to be represented in XML. Data types are reusable atomic building blocks used to create all HL7 V3 information structures. Each RIM attribute is assigned one data type; each data type is assigned to zero, one, or more RIM attribute. Few of HL7V3.0 data types are given below
• AD: Postal Address
• ANY: DataValue
• BAG: Bag
• BL: Boolean
• CD: Concept Descriptor
• CE: Coded With Equivalents
• CS: Coded Simple Value
• ED: Encapsulated Data
• EN: Entity Name
• GTS: General Timing Specification
• HIST: History
• II: Instance Identifier
• INT: Integer Number
• IVL: Interval
• LIST: Sequence
• MO: Monetary Amount
• ON: Organization Name
• PN: Person Name
• PPD: Parametric Probability Distribution
• PQ: Physical Quantity
• REAL: Real Number
• RTO: Ratio
• SC: Character String with Code
• SET: Set
• ST: Character String
• TEL: Telecommunication Address
• TN: Trivial Name
• TS: Point in Time
• UVP: Uncertain Value – Probabilistic
HL7V3.0 Vocabulary Specification:
The HL7 V3 Vocabulary Specification defines vocabulary domains used in RIM coded Attributes and coded data type properties. A vocabulary domain is an abstract collection of interrelated concepts. It describes the purpose or intent of a coded attribute. A value set is a collection of coded concepts drawn from a single code system. A vocabulary domain may be associated with many value sets. A context expression provides a means of designating which value sets within a given domain are applicable for a given usage context. A coded concept has a concept code assigned by the coding system and a concept designation which names the referenced concept. A coded concept may be a parent concept for a collection of additional concepts within the same code system.
HL7 XML Schema Generator:
The HMD’s constrained with HL7 Vocabulary Specification and HL7 Data Type specification to a HL7XML schema Generator gives the XSD the schema definition of an HL7V3.0 message. Figure below shows the set up for the generation of XSD.
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