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, .
• Loot, .
• Bag,
• Get away car, .

The Roles might be:

• Robber, .
• Cashier, .
• Bank Manager, .
• Policeman, .

The Entry Conditions might be:

• is poor.
• is destitute.

The Results might be:

• has more money.
• is angry.
• is in a state of shock.
• is shot.

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

The full Script could be described in Fig .

Fig. 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.