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The FROM clause utilises class expressions and a set of containment criteria to specify the data source from which the query required data is to be retrieved. Its function is similar as the FROM clause of an SQL expression.
FROM Syntax
A simple FROM clause consists of three parts: keyword - FROM, class expression and/or containment constraints, e.g.
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EHR e [ehr_id/value=$ehrId] \\EHR class, class identifier/variable, and a standard predicate COMPOSITION c[openEHR-EHR-COMPOSITION.report.v1] \\COMPOSITION class, class identifier/variable, and an archetype predicate |
Class expressions are used for two purposes:
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