message RelationshipFilter {
    string resource_type = 1;
    string optional_resource_id = 2;
    string optional_relation = 3;
    SubjectFilter optional_subject_filter = 4;
}

{
  "consistency": {
    "minimizeLatency": true
  },
  "relationshipFilter": {
    "resourceType": "document",
    "optionalResourceId": "",
    "optionalRelation": ""
  }
}