Example of eventdefinition

{
  "resourceType" : "EventDefinition",
  "id" : "example",
  "extension" : [{
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-wg",
    "valueCode" : "cds"
  }],
  "status" : "draft",
  "publisher" : "HL7 International / Clinical Decision Support",
  "contact" : [{
    "telecom" : [{
      "system" : "url",
      "value" : "http://www.hl7.org/Special/committees/dss"
    }]
  }],
  "purpose" : "Monitor all admissions to Emergency",
  "trigger" : [{
    "type" : "named-event",
    "name" : "monitor-emergency-admissions",
    "data" : [{
      "type" : "Encounter"
    }],
    "condition" : {
      "description" : "Encounter Location = emergency (active/completed encounters, current or previous)",
      "language" : "text/fhirpath",
      "expression" : "(%current | %previous).location.where(location = 'Location/emergency' and status in {'active', 'completed'}).exists()"
    }
  }]
}