Conceptual Dependency (CD)

Conceptual Dependency originally developed to represent knowledge acquired from natural language input.

The goals of this theory are:

• To help in the drawing of inference from sentences.
• To be independent of the words used in the original input.
• That is to say: For any 2 (or more) sentences that are identical in meaning there should be only one representation of that meaning.

It has been used by many programs that portend to understand English (MARGIE, SAM, PAM). CD developed by Schank et al. as were the previous examples.

CD provides:

• a structure into which nodes representing information can be placed
• a specific set of primitives
• at a given level of granularity.

Sentences are represented as a series of diagrams depicting actions using both abstract and real physical situations.

• The agent and the objects are represented
• The actions are built up from a set of primitive acts which can be modified by tense.

Examples of Primitive Acts are:

ATRANS

-- Transfer of an abstract relationship. e.g. give.

PTRANS

-- Transfer of the physical location of an object. e.g. go.

PROPEL

-- Application of a physical force to an object. e.g. push.

MTRANS

-- Transfer of mental information. e.g. tell.

MBUILD

-- Construct new information from old. e.g. decide.

SPEAK

-- Utter a sound. e.g. say.

ATTEND

-- Focus a sense on a stimulus. e.g. listen, watch.

MOVE

-- Movement of a body part by owner. e.g. punch, kick.

GRASP

-- Actor grasping an object. e.g. clutch.

INGEST

-- Actor ingesting an object. e.g. eat.

EXPEL

-- Actor getting rid of an object from body. e.g. ????.

Six primitive conceptual categories provide building blocks which are the set of allowable dependencies in the concepts in a sentence:

PP     

-- Real world objects.

ACT

-- Real world actions.

PA

-- Attributes of objects.

AA

-- Attributes of actions.

T

-- Times.

LOC

-- Locations.

How do we connect these things together?

Consider the example:

John gives Mary a book

• Arrows indicate the direction of dependency. Letters above indicate certain relationships:

o

-- object.

R

-- recipient-donor.

I

-- instrument e.g. eat with a spoon.

D

-- destination e.g. going home.

• Double arrows () indicate two-way links between the actor (PP) and action (ACT).
• The actions are built from the set of primitive acts (see above).
• These can be modified by tense etc.

The use of tense and mood in describing events is extremely important and schank introduced the following modifiers:

p

-- past

f

-- future

t

-- transition

-- start transition

-- finished transition

k

-- continuing

?

-- interrogative

/

-- negative

delta

-- timeless

c

-- conditional

the absence of any modifier implies the present tense.

So the past tense of the above example:

John gave Mary a book becomes:

The  has an object (actor), PP and action, ACT. I.e. PP  ACT. The triplearrow () is also a two link but between an object, PP, and its attribute, PA. I.e. PP  PA.

It represents isa type dependencies. E.g

Dave  lecturerDave is a lecturer.

Primitive states are used to describe many state descriptions such as height, health, mental state, physical state.

There are many more physical states than primitive actions. They use a numeric scale.

E.g. John  height(+10) John is the tallest John  height(< average) John is short Frank Zappa  health(-10) Frank Zappa is dead Dave  mental_state(-10) Dave is sad Vase physical_state(-10) The vase is broken

You can also specify things like the time of occurrence in the relation ship.

For Example: John gave Mary the book yesterday

Now let us consider a more complex sentence: Since smoking can kill you, I stopped Lets look at how we represent the inference that smoking can kill:

• Use the notion of one to apply the knowledge to.
• Use the primitive act of INGESTing smoke from a cigarette to one.
• Killing is a transition from being alive to dead. We use triple arrows to indicate a transition from one state to another.
• Have a conditional, c causality link. The triple arrow indicates dependency of one concept on another.

To add the fact that I stopped smoking

• Use similar rules to imply that I smoke cigarettes.
• The qualification  attached to this dependency indicates that the instance INGESTing smoke has stopped.

Advantages of CD:

• Using these primitives involves fewer inference rules.
• Many inference rules are already represented in CD structure.
• The holes in the initial structure help to focus on the points still to be established.

Disadvantages of CD:

• Knowledge must be decomposed into fairly low level primitives.
• Impossible or difficult to find correct set of primitives.
• A lot of inference may still be required.
• Representations can be complex even for relatively simple actions. Consider:

Dave bet Frank five pounds that Wales would win the Rugby World Cup.

Complex representations require a lot of storage

Applications of CD:

MARGIE

(Meaning Analysis, Response Generation and Inference on English) -- model natural language understanding.

SAM

(Script Applier Mechanism) -- Scripts to understand stories. See next section.

PAM

(Plan Applier Mechanism) -- Scripts to understand stories.