CQL Execution VSAC Code Service

This project establishes a VSAC-enabled code service module for use with the CQL Execution Engine. This allows the CQL Execution Engine to execute CQL containing references to Value Sets that are published in the National Library of Medicine's (NLM) Value Set Authority Center (VSAC). Value Set references can be defined using a valid VSAC identifying URL for the value set, a URN, or the oid itself. For example:

valueset "Diabetes": 'https://cts.nlm.nih.gov/fhir/ValueSet/2.16.840.1.113883.3.464.1003.103.12.1001'
// or valueset "Diabetes": 'urn:oid:2.16.840.1.113883.3.464.1003.103.12.1001'
// or valueset "Diabetes": '2.16.840.1.113883.3.464.1003.103.12.1001'

This library requires that the credentials of a valid UMLS account be provided to it. If you do not have an UMLS account, you can request one here: https://uts.nlm.nih.gov/license.html

Setting Up the Environment

To use this project, you should perform the following steps:

1. Install Node.js
2. Install Yarn
3. Execute the following from this project's root directory: yarn

Using the VSAC Code Service

The Local Cache

The VSAC Code Service is constructed with a file path pointing to the location where the cache should be stored. If a file location is not passed into the constructor, it will default the cache to a folder called vsac_cache in the working directory. The cache is used to store value sets and their codes after retrieving them from VSAC. This prevents the code service from having to make multiple calls to VSAC for the same value set.

The second argument to the CodeService constructor is a boolean indicating if the code service should begin by loading existing value sets from the cache. If true, it will initialize the code service from the cache (if the cache exists and is populated). If false, ensureValueSets will re-download any value sets passed to it, overwriting the cache.

Using UMLS Credentials

Downloading value set definitions from VSAC requires a valid UMLS account. The code service's ensureValueSets function allows a UMLS username and password to be passed in. Alternately, the UMLS username and password can be provided via UMLS_USER_NAME and UMLS_PASSWORD environment variables.

Downloading Value Set Definitions

The ensureValueSets and ensureValueSetsInLibrary functions are the only functions that attempt to download value sets from VSAC. Before they make a request to VSAC, they will check the cache. If the value set is already in the cache, they will not make a request to VSAC. Otherwise, they will use VSAC's SVS2 API to download the expanded codes from the value set.

The findValueSet and findValueSets functions (including the legacy findValueSetsByOid function) do not reach out to VSAC, so implementations should call ensureValueSetsInLibrary or ensureValueSets before attempting to execute CQL. If ensureValueSets is used, the implementor is responsible for passing in the OIDs / versions that will be needed.

Example

The following is a simple example of setting up the VSAC Code Service, calling ensureValueSets, and passing the Code Service into the CQL Execution engine:

const vsac = require('cql-exec-vsac');

// Code setting up the CQL library, patient source, parameters, etc
// ...

// Set up the code service, loading from the cache if it exists
const codeService = new vsac.CodeService('/path/to/vsac_cache', true);
// Ensure value sets in the library and its dependencies, downloading any missing value sets
codeService.ensureValueSetsInLibrary(library, true, 'myUMLSUserName', 'myUMLSPassword')
.then(() => {
  // Value sets are loaded, so execute!
  const executor = new cql.Executor(lib, codeService, parameters);
  const results = executor.exec(patientSource);
  // Do something with results...
})
.catch( (err) => {
  // There was an error downloading the value sets!
  console.error('Error downloading value sets', err);
});

Linting the Code

To encourage quality and consistency within the code base, all code should pass eslint without any warnings. Many text editors can be configured to automatically flag eslint violations. We also provide an npm script for running eslint on the project. To run eslint, execute the following command:

$ yarn lint