This code system http://hl7.org/fhir/trigger-type defines the following codes:

CodeDisplayDefinition
named-eventNamed EventThe trigger occurs in response to a specific named event
periodicPeriodicThe trigger occurs at a specific time or periodically as described by a timing or schedule
data-addedData AddedThe trigger occurs whenever data of a particular type is added
data-modifiedData ModifiedThe trigger occurs whenever data of a particular type is modified
data-removedData RemovedThe trigger occurs whenever data of a particular type is removed
data-accessedData AccessedThe trigger occurs whenever data of a particular type is accessed
data-access-endedData Access EndedThe trigger occurs whenever access to data of a particular type is completed