3.16.2 Abstract Event Type

   (136) <event_abs_dcl> ::= “abstract? “eventtype? <identifier> [ <value_inheritance_spec> ] “{? <export>* “}?

   Event types may also be abstract. They are called abstract because an abstract event type may not be instantiated. No <state_member> or <initializers> may be specified. However, local operations may be specified. Essentially they are a bundle of operation signatures with a purely local implementation.

   Note that a concrete event type with an empty state is not an abstract event type.