Scripts

A script is a structure that prescribes a set of circumstances which could be expected to follow on from one another.

It is similar to a thought sequence or a chain of situations which could be anticipated.

It could be considered to consist of a number of slots or frames but with more specialised roles.

Scripts are beneficial because:

• Events tend to occur in known runs or patterns.
• Causal relationships between events exist.
• Entry conditions exist which allow an event to take place
• Prerequisites exist upon events taking place. E.g. when a student progresses through a degree scheme or when a purchaser buys a house.

The components of a script include:

Entry Conditions

-- these must be satisfied before events in the script can occur.

Results

-- Conditions that will be true after events in script occur.

Props

-- Slots representing objects involved in events.

Roles

-- Persons involved in the events.

Track

-- Variations on the script. Different tracks may share components of the same script.

Scenes

-- The sequence of events that occur. Events are represented in conceptual dependency form.

Scripts are useful in describing certain situations such as robbing a bank. This might involve:

• Getting a gun.
• Hold up a bank.
• Escape with the money.

Here the Props might be

• Gun, G.
• Loot, L.
• Bag, B
• Get away car, C.

The Roles might be:

• Robber, S.
• Cashier, M.
• Bank Manager, O.
• Policeman, P.

The Entry Conditions might be:

• S is poor.
• S is destitute.

The Results might be:

• S has more money.
• O is angry.
• M is in a state of shock.
• P is shot.

There are 3 scenes: obtaining the gun, robbing the bank and the getaway.

The full Script could be described in Fig 19.

Fig. 12 Simplified Bank Robbing Script

Some additional points to note on Scripts:

• If a particular script is to be applied it must be activated and the activating depends on its significance.
• If a topic is mentioned in passing then a pointer to that script could be held.
• If the topic is important then the script should be opened.
• The danger lies in having too many active scripts much as one might have too many windows open on the screen or too many recursive calls in a program.
• Provided events follow a known trail we can use scripts to represent the actions involved and use them to answer detailed questions.
• Different trails may be allowed for different outcomes of Scripts ( e.g. The bank robbery goes wrong).

Advantages of Scripts:

• Ability to predict events.
• A single coherent interpretation may be build up from a collection of observations.

Disadvantages:

• Less general than frames.
• May not be suitable to represent all kinds of knowledge.