Logic Modelling Workshop

Activities in the ZOO world

Types and features

The active structure consists of phenomena that may change over time, and that in particular may change positions within the landscape structure. The active structure of the ZOO world uses one type besides the types in the landscape structure, namely:

• animals

Each animal belongs to exactly one of a number of species. All the species are named and explicitly known. The membership of an animal in a species does not change over time. The species human is always defined, and there is at least one human-species animal in each scenario.

Each animal also has the boolean properties large and adult. Some species are large, some are not. Adult members of large species are large animals; all other animals are small (non-large).

Each animal has a position at each point in time. Two large animals can not occupy the same position, except if one of them rides on the other (see below).

Movement

Animals can move. In one unit of time, an animal can move to one of the positions adjacent to its present one, or stay in the position where it is. Moves to non-adjacent positions are never possible. Movement is only possible to positions within the same location (for example, within the same cage), and between those two positions that are to the side of the same gate, but only provided the gate is open. Several animals can move at the same time.

Movement actions must also not violate the occupancy restriction: at most one large animal in each position. This restriction also holds within the duration of moves, in the sense that a concurrent move where animal A moves into a position at the same time as animal B moves out of it, is only possible if at least one of A and B is a small animal.

This means in particular that two large animals can not pass through a gate at the same time (neither in the same direction nor opposite directions).

Actions

The following actions can be performed by animals. (Objects of the types in the landscape structure can not perform actions).

• Move To Position. Can be performed by any animal, under the restrictions described above, plus the restriction that a human riding an animal can not perform the Move-To-Position action (compare below).

• Open Gate. Can be performed by a human when it is located in a position to the side of the gate, and has the effect that the gate is then open until the next time a Close Gate action is performed.

• Close Gate. Can be performed by a human when it is located in a position to the side of the gate, and has the effect that the gate is closed until the next time an Open Gate action is performed.

• Mount Animal. Can be performed by a human mounting a large animal, when the human is in a position adjacent to the position of the animal. The action fails if the animal moves at the same time, and in this case the result of the action is that the human moves to the position where the animal was. If successful, the action results in a state where the human rides the animal. This condition holds until the human performs a Getoff action or the animal performs a Throwoff action.

  When a human rides an animal, the human can not perform the Move action, and its position is the same as the animal's position while the animal moves.

• Getoff Animal to Position. Can be performed by a human riding an animal, to a position adjacent to the animal's present position provided that the animal does not move at the same time. Fails if the animal moves, and in this case the rider stays on the animal.

• Throwoff. Can be performed by an animal ridden by a human, and results in the human no longer riding the animal and ending in a position adjacent to the animal's present position. The action is nondeterministic since the rider may end up in any such position. If the resultant position is occupied by another large animal then the human will result in riding that animal instead.

It is recognized that this specification still leaves a few details open, for example, what is to happen if an animal performs a Throwoff whereby the rider goes to a position where, concurrently, another large animal is moving in or moving out. Each axiomatization ought to identify those open questions and indicate what choice it has implemented for each of them.

Restricted and Extended Scenario Worlds

The ZOO scenario world is relatively complex, and offers a number of difficulties. Axiomatizations of simplified versions of the ZOO world are of course welcome, as well as axiomatizations of extended worlds with additional features. However, all restrictions and extensions should be clearly specified in the technical note describing the axiomatization.

Maintenance information:

Latest update 21.6.1999 by EMTEK group. Edit mode aml, position code C.lmw.ZOO.activities.