The SNOMED CT content by which an expression constraint is evaluated or a query is executed.
Two distinct types of substrate are directly relevant to use of SNOMED CT:
The substrate for an expression constraint that generates the membership of a subset or reference set.
The substrate for a clinical analytics query, consisting of a collection of records either coded in or mapped to SNOMED CT.
Substrates for subset generation include:
A particular version of a specified SNOMED CT edition
Members of a preexisting reference set.
SNOMED CT encoded electronic health records from a particular institution or department.
A disease registry database containing or mapped to SNOMED CT.