Knowledge Structures

Common Sense Reasoning

Recall that in the case of Frames we have Slots and Fillers

Frame
SLOTS	FILLER

Frames can have some slots in common.

Consider the following sentence:

Bill shot Bob.

We understand that Bill has a gun and uses the gun to shoot Bob.á After which Bob is probably not very happy.á A natural language sentence is likely to have a number of hidden meanings. Hidden meanings are not obvious in the structure of the sentence.á

For the example of the earthquake

Earthquake
SLOTS	FILLER
Time
Place
Damages
Casualties

For events other than Earthquake (Bill shot Bob, or go get coffee please, or Xerox this), the slots Time, Place, etc are not necessarily appropriate.á Should we create a new frame for each event then?á The number of frames (our vocabulary) would just keep increasing and increasing.á Instead let us define a canonical vocabulary, a standard vocabulary that will work for some set of sentences (not all sentences, but some subset).á For the moment let us consider only sentences which have to do with intentional agents who do actions.á

We will call this standard vocabulary our Ontology.á

Ontology: án : the metaphysical study of the nature of being and existence

Source: WordNet « 1.6, ¨ 1997 Princeton University

Here is a standard vocabulary that has evolved for intentional agents doing actions.á It is the Ontology of Thematic Roles.á It has the following kind of slots for a frame:

Agentáááááááááááááááááááááááááááááááááááááá - Robbie kicked a ball.
Co-agentááááááááááááááááááááááááááááááááá - Robbie and Sue were playing tennis.
Beneficiery/Recipientááááááááááááááá - Tom carried ice cream to Susan.
Objectá
Time
Duration
Locationáááááááááááááááááááááááááááááááááá - Tom was playing soccer in Atlanta.
Source
Destination
Instrumentááááááááááááááááááááááááááááááá - Tom eats ice cream with a spoon.

With these few roles we can cover a large number of sentences.

Consider the following sentence:

John gave a book to Mary.

One can ask, ôWho had the book?öá We know that Mary did because of our common sense reasoningáá

John gave a book to Mary
SLOTS	FILLER
Agent	John
Co-Agent	<unspecified>
Beneficiary	Mary
Object	Book
Time	<unspecified>
Location	<unspecified>
Instrument	<unspecified>
Source	?
Destination	?

Two procedures to act on this frame.

Writeááá - takes a frame and fills in a slot
Readááá - when posed with a query will look at the fillers and give an answer

John got a book from Mary.

John was given a book by Mary.

Mary gave a book to John.

The three sentences above, even though they are syntactically different, have the same meaning.á Mary is the agent, John is the beneficiary, and the book is the object.

State Changes

Susie comforted Tom.

John ate ice cream with a spoon.
SLOTS	FILLER
Agent	John
Co-Agent	<unspecified>
Beneficiary	<unspecified>
Object	Ice cream
Time	<unspecified>
Location	<unspecified>
Instrument	spoon
Source	?
Destination	?
Result	John is less hungry. There is less ice cream

Focus on the prepositions.á Whatever comes after ôwithö is a candidate for an instrument.á However the sentence could read ôJohn ate ice cream with Maryö in which case ôMaryö is not an instrument.á

Now we add a slot to the frame called Result.á The problem is that there is nothing in our Ontology to capture a state change.

John drank soda with a straw.

John ate ice cream with a spoon.

Both sentences (and many others like them) express forms of ingestion.á So let us make an ontology of primitive actions.


Physical World	Mental World
INGEST

A-Trans	M-Build
P-Trans

Mental world has to do with ôI believe that John was my friend.ö û concepts that are in the mind.á

A-Trans: abstract transferáááááááá - John got a book from Mary.

ááááááááááááááááááááááááááááááááááááááááááááááá - John stole the book.

P-Trans: physical transferááááááááá - John ran with the book.

M-Build:áááááááááááááááááááááááááááááááááá - John had a nightmare last night.

All of the slots are the same for the vocabulary that comes from the frame INGEST:á (eat, drink, inhale, consume, inject, sniff, imbibe, etc).á However, the vocabulary may not be the same for A-Trans and P-Trans slots.á

When processing a sentence, if a verb is encountered that is a form of ingestion, then the frame INGEST pops out of memory.á The frame then drives the processing to fill in as many of the missing fillers as possible.

Attached to Results Slot of ôJohn ate ice cream àö		Attached to Results Slot of ôJohn ate ice cream à ô
SLOTS	FILLERS	SLOTS	FILLERS
Object	Ice cream	Object	John
Source	Outside John	Result	happy
Destination	Inside John

One result is that there is an object ice cream that has a source outside John and a destination inside John.á Some state change occurs.á (There can be more results of course).á We can ask how is John feeling at the end.á A read procedure can look for JohnÆs mood and respond with that value.á

Knowledge structures is like a fish hook.á There is not one hook, but a large number of them.á So understanding is like we have a special kind of hook that corresponds to ingestion.á That sharp hook says ôLook for an instrument, thereÆs probably an instrument involved.öá So a lot of knowledge is built in along with each primitive action.á

There are some problems with this approach.á If ôhappyö is associated as a result of drinking alcohol then

Mary drank gin.

will result in the conclusion that Mary is happy.á We could also say

Mary drank a lot of gin.

The conclusion would still be that Mary is happy, but this might not be true.á So we need to build additional rules for differing amounts of gin.