Since its introduction, the action description language 
of
Gelfond and Lifschitz [GL93] has served as a platform to study
several aspects that arise in the formalization of action theories.
was designed as a minimal core of a high level language to
represent and reason about actions and their effects. Domain
descriptions written in this language have direct translations into
extended logic programs. Extensions of have been developed to
study and reason about the concurrent execution of actions, the
non-deterministic effects of some actions and to study many instances
of the qualification and ramification problems.
Baral at University of Texas at El Paso, together with his students
has implemented a liner planner based on [Kah96] that
compares very well to standard planners such as UCPOP [BCF+95],
one of the most commonly used (partial order) planners.
In [LMT97] we had proposed a new action description language
called K . K is a minimal extension of
to handle sensing actions. A sensing action is an action that does
not have any effect in the world. The effect is only in the
perception of the reasoning agent about the world. The execution of a
sensing action will increase the agent knowledge about the current
state of the world. Take for example a deactivated agent placed
inside a room. The agent has duties to carry out and will be activated
by a timer. Let us assume the agent is always placed facing the door.
The agent, once activated, may become damaged if it attempts to leave
the room since the door may be closed. Before the agent tries to leave
the room it needs to perform some act of sensing in order to determine
whether the door is opened or not. The agent has incomplete knowledge
with respect to the door. A sensing action such as looking at the door
would provide information to the agent concerning the status of the
door. The major advantage of adding sensing action is that they give
an agent the ability to reason about complex plans that include
conditionals and iterations [Lev96].