The Act.classCode is a structural code which specifies the general nature of the Act. Its values are drawn from the HL7 ActClass vocabulary table.
The Act.classCode has the effect of specializing the Act class and, as a result, constrains the vocabulary domains that apply to other coded attributes of that class. If a SNOMED CT expression is used to encode the values of one or more of these other attributes, the meaning of the expression must be appropriate to the constrained vocabulary domain.
The vocabulary domain constraints applicable to specific SNOMED CT encoded attributes of different HL7 classes are specified in SNOMED CT vocabulary domain constraints.
The rationale for the vocabulary domain constraints applicable to particular HL7 classes are discussed in SNOMED CT vocabulary domain constraints. This is supplemented by Detailed aspects of issues with a vocabulary specification formalism, which discusses different ways in which constraints may need to be expressed to take account of the SNOMED CT terminology model.