AI LECT 13

STRONG SLOT & FILLER STRUCTURES

So far the structures we have used have been general and there is therefore much freedom in the choice of the links between objectsand the inference procedures set up.  Schank in 1973 and 1975 developed the theory of Conceptual Dependency known as CD to represent knowledge acquired from natural language input.  The goals of this theory are
to help in the drawing of inference in sentences;
to be independent of the words used in the original input.
It has been used by many programs that portend to understand English.
CD provides both a structure into which nodes representing information can be placed and a specific set of primitives at a given granularity.  Examples of this theory are on  page 2.
We see how sentences are represented as a seires of diagrams depicting actions using both abstract and real physical situations.  The agent and the objects are represented and the actions are built up from a set of primitive acts.  These can be modified by tense.  
In addition four building blocks are introduced which are the set of allowable dependencies in  the concepts in a sentence. They are
ACT	actions
PP	objects	picture producers
AA	action modifiers	action aiders
PA	object modifiers	picture aiders
The rules and the dependencies are now displayed on page 3.
The use of tense and mood in describing events is extremely importantand schank introduced the following modifiers
past p;  future f;  transition t; start transition ts;  finished transition tf;  continuing k;
interrogative ?;negative /;  present nil; timeless delta; conditional c;
Consider the sentence
Since smoking can kill you, I stopped depicted in fig 10.3 where the vertical causality link indicates killing and the c modifier says that it is probabilistic. The horizontal link says that it was this that made me stop and tfp shows that it has stopped in the past.
Using CD means that
1	Using these primitives involves fewer inference rules;
2	many inference rules are already represented;
3	the holes in the inital structure help to focus on the points still to be established.
The use of CD primitives means that the effect of the verbs  give, steal, donate, take; 
can all be coveredby the primitive ACT ATRANS involving the transfer of ownership.
In fig 10.4 the sentence Bill threatened John with a broken nose is considered.
The CD representation is built up from information in the sentence and associate inference rules and once represented can be used repeatedly.  The key to this representation lies in the interpretation of what is in John’s mind following Bill’s remark.  The dummy objects do1 do2 indicate that we can expect information about what John might do that Bill does not want.
SCRIPTS
A script is a structure that precribes 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 consists of a number of slots or frames.
The components of scripts are given on page 4.  

Scripts are beneficial because events tend to occur in known runs or patterns. There are causal relationships between events.  There are entry conditions which allow an event to take place and as a result of this event the succedding event is chosen depending on the prerequisites much as when a student progresses through a degree scheme or when a purchaser buys a house.

Scripts are useful in certain situations such as buying a dress and ordering and eating a meal.
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.
see the first story on page 4

In the second story 
Susan went out to lunch.  She sat down at a table and called the waitress.  The waitress brought her a menu and she ordered a hamburger.
The question is   Why did the waitress bring Susan a menu?
Script gives two answers
Because Susan asked her to		via the causal chain not helpful
So that Susan could decide what she wanted to eat     which event is enabled  better

Another story
John went to a restaurant.  He was shown to his table.  He ordered a large steak.  
He sat there and waited for a long time.  He got mad and left.

Where did this final action leave the anticipated progress in the script.  Not in being shown a table but associated with the waiting for the meal to arrive.
Once the path of events is broken we cannot guess what may happen, we do not know where John went whether he paid the bill or not.

Provided events follow a known trail we can use scripts to represent the actions and use them to answer detailed questions.