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2.1 Introduction

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When used together SNOMED CT and HL7 often offer multiple possible approaches to representing the same clinical information. This need not be a problem where clear rules can be specified that enable transformation between alternative forms. However, unambiguous interpretation and thus reliable transformation depends on understanding the semantics of both the RIM and HL7 and guidelines to manage areas of overlap or apparent conflict.

Key to phrases used in this section
Phrase Meaning Examples
[RimClass] class

The HL7 Version 3 Reference Information Model class named [RimClass].

"Act class" - refers to the RIM class Act as specified in the RIM.
[RimClass] class specialization

Any class in the RIM that is a specialization of the named [RimClass].

"Act class specialization" - refers to any RIM class that is model as specialization of Act in the RIM. For example, the "Observation
[RimClass] class clone A class in a constrained information model (e.g. an DMIM, RMIM, HMD or template) that is derived from one of the following:
  • the named [RimClass]
  • a [RimClass] class specialization.
"Observation class clone" - refers to any design time constraint on the Observation class.

This may be part of a domain model, a message design specification or template.

[RimClass] class instance An instance of information structured in accordance with one of the following:
  • the named [RimClass]
  • a [RimClass] class specialization
  • a [RimClass] clone.
"Act class instance" - refers to an instance of run time information structured in accordance with either the Act class or
                                   any specialization or constraint applied to the Act class.
[RimClass].[Attribute] The named [Attribute] in any of the following:
  • the named [RimClass]
  • a [RimClass] class specialization
  • a [RimClass] clone
  • a [RimClass] instance
"Act.code" refers the "code" attribute of either the Act class itself or of an Act class specialization (.e.g. Observation,

In contrast, "Observation.code" refers specifically to the "code" attribute of an Observation class.

SNOMED CT expression One or more SNOMED CT concept identifiers used to represent meaning. See the examples for "Pre-coordinated expression" and "Post-coordinated expression" in the following two rows.
Pre-coordinated expression A SNOMED CT expression containing only one SNOMED identifier. In an HL7 attribute any of the coded data types can be used
                                   to represent a pre-coordinated expression.

<value code="195967001|asthma|" codeSystem="2.16.840.1.113883.6.96"/>

Post-coordinated expression A SNOMED CT expression containing more than one SNOMED identifier. In an HL7 attribute the Concept Descriptor (CD) data type
                                   is used to represent a post-coordinated expression.

It appears that Datatypes R2 is presumed here? Will need to check for references to Datatypes R1 qualifiers, and make sure that we are consistent. Presumably we need to cover both, since CDA uses R1? RH

<value codeSystem="2.16.840.1.113883.6.96" code="195967001|asthma|:246112005|severity|=24484000|severe|"/>