Library — detail: CQL & FHIRPath container
Carrier of executable logic (CQL, FHIRPath, ELM) referenced by Measure, PlanDefinition, ActivityDefinition. Foundation brick of HEDIS / QPP quality measures and evidence-based clinical decisions.
Role in clinical reasoning
Library is the core asset of the Clinical Quality Language (CQL) pattern. A Library carries the executable CQL code that other resources reference:
- Measure ->
library-> Library (population, numerator, denominator). - PlanDefinition ->
library-> Library (CDS rules). - ActivityDefinition ->
library-> Library (attribute computation).
Key fields
| Field | Cardinality | Role |
|---|---|---|
url | 0..1 | Canonical URL referenced by Measure / PlanDefinition. |
version | 0..1 | Semantic version. |
status | 1..1 | draft | active | retired | unknown. |
type | 1..1 | logic-library | model-definition | asset-collection | module-definition. |
content | 0..* | Attachments. Text CQL, ELM XML/JSON. |
dataRequirement | 0..* | FHIR data consumed (useful for pre-fetch). |
parameter | 0..* | Execution parameters. |
Embedded CQL
The content block embeds CQL as base64 (contentType: text/cql)
or points to an external attachment (url). The server compiles to ELM
(Expression Logical Model) before execution.
Example: HbA1c measure Library
{
"resourceType": "Library",
"id": "lib-hba1c-measure",
"url": "http://example.org/fhir/Library/HbA1cMeasure",
"version": "1.0.0",
"name": "HbA1cMeasure",
"title": "HbA1c Quality Measure CQL Library",
"status": "active",
"experimental": false,
"type": {
"coding": [{
"system": "http://terminology.hl7.org/CodeSystem/library-type",
"code": "logic-library"
}]
},
"subjectCodeableConcept": {
"coding": [{
"system": "http://hl7.org/fhir/resource-types",
"code": "Patient"
}]
},
"content": [{
"contentType": "text/cql",
"data": "bGlicmFyeSBIYkExY01lYXN1cmUgdmVyc2lvbiAnMS4wLjAnCnVzaW5nIEZISVIgdmVyc2lvbiAnNS4wLjAnCmluY2x1ZGUgRkhJUkhlbHBlcnMgdmVyc2lvbiAnNS4wLjAnCgpwYXJhbWV0ZXIgIk1lYXN1cmVtZW50IFBlcmlvZCIgSW50ZXJ2YWw8RGF0ZVRpbWU+Cgpjb250ZXh0IFBhdGllbnQK"
}]
}Common pitfalls
- No version — without
version, audit traceability breaks. - Uncompilable CQL — a broken CQL attachment fails consuming Measures. Unit test in pre-publication.
- Missing dataRequirement — without, the server cannot pre-fetch data.