This code system http://hl7.org/fhir/hl7-work-group defines the following codes:

CodeDisplayDefinition
cbccCommunity Based Collaborative CareCommunity Based Collaborative Care (http://www.hl7.org/Special/committees/cbcc/index.cfm)
cdsClinical Decision SupportClinical Decision Support (http://www.hl7.org/Special/committees/dss/index.cfm)
cqiClinical Quality InformationClinical Quality Information (http://www.hl7.org/Special/committees/cqi/index.cfm)
cgClinical GenomicsClinical Genomics (http://www.hl7.org/Special/committees/clingenomics/index.cfm)
devHealth Care DevicesHealth Care Devices (http://www.hl7.org/Special/committees/healthcaredevices/index.cfm)
ehrElectronic Health RecordsElectronic Health Records (http://www.hl7.org/special/committees/ehr/index.cfm)
fhirFHIR InfrastructureFHIR Infrastructure (http://www.hl7.org/Special/committees/fiwg/index.cfm)
fmFinancial ManagementFinancial Management (http://www.hl7.org/Special/committees/fm/index.cfm)
hsiHealth Standards IntegrationHealth Standards Integration (http://www.hl7.org/Special/committees/hsi/index.cfm)
iiImaging IntegrationImaging Integration (http://www.hl7.org/Special/committees/imagemgt/index.cfm)
inmInfrastructure And MessagingInfrastructure And Messaging (http://www.hl7.org/special/committees/inm/index.cfm)
itsImplementable Technology SpecificationsImplementable Technology Specifications (http://www.hl7.org/special/committees/xml/index.cfm)
ooOrders and ObservationsOrders and Observations (http://www.hl7.org/Special/committees/orders/index.cfm)
paPatient AdministrationPatient Administration (http://www.hl7.org/Special/committees/pafm/index.cfm)
pcPatient CarePatient Care (http://www.hl7.org/Special/committees/patientcare/index.cfm)
pherPublic Health and Emergency ResponsePublic Health and Emergency Response (http://www.hl7.org/Special/committees/pher/index.cfm)
phxPharmacyPharmacy (http://www.hl7.org/Special/committees/medication/index.cfm)
rcrimRegulated Clinical Research Information ManagementRegulated Clinical Research Information Management (http://www.hl7.org/Special/committees/rcrim/index.cfm)
sdStructured DocumentsStructured Documents (http://www.hl7.org/Special/committees/structure/index.cfm)
secSecuritySecurity (http://www.hl7.org/Special/committees/secure/index.cfm)
usUS Realm TaskforceUS Realm Taskforce (http://wiki.hl7.org/index.php?title=US_Realm_Task_Force)
vocabVocabularyVocabulary (http://www.hl7.org/Special/committees/Vocab/index.cfm)
aidApplication Implementation and DesignApplication Implementation and Design (http://www.hl7.org/Special/committees/java/index.cfm)