Filters allow the user to specify visibility predicates, which are expressions relating attributes and their values. HAM filters only return objects that satisfy the predicates. Filters also allow the user to specify a version time so that earlier versions of a graph can be examined. Attaching an ACL to an object is optional. An ACL entry consists of a user or group name and a set of permissions.
Possible permissions are access, annotate, update and destroy.
Most permissions have an obvious meaning.