Knowledge Representation

What is Knowledge Representation

Type of knowledge in AI Declarative knowledge

Procedural Knowledge

Knowledge Representation Schemes Semantic Networks

Frames

Scripts

Conceptual Dependency

A Representation is a way of describing certain fragments or information so that any reasoning system can easily adopt it for inferencing purposes.

Knowledge representation is a study of ways of how knowledge is actually picturized and how effectively it resembles the representation of knowledge in human brain.

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Declarative knowledge Procedural knowledge

A declarative representation declare every piece of knowledge.

For Exp:-“All carnivorous have sharp teeth”,“Cheetah is a carnivore”.

This can be represented using a Declarative representation as V x (carnivore (x) sharp_teeth (x))

Carnivore(Cheetah)

Using this two representation, it is possible to deduce that “Cheetah has sharp teeth”

A Procedural knowledge represents knowledge as procedure and the inferencing mechanism manipulate these procedure to arrive at the result.

For Exp:-Procedure carnivore(x);

if (x= cheetah) then return trueelse return false

end procedure carnivore (x). procedure sharp_teeth (x);

if carnivore (x) then return trueelse return false

end procedure sharp_teeth (x)

To see whether cheetah has sharp teeth, one should activate procedure sharp_teeth with variable x instantiated to value cheetah.

This procedure calls procedure carnivore (x) in turn with the value of (x = cheetah).

Procedure carnivore returns a true value and so is procedure sharp_teeth.

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Semantic nets

Frames

Conceptual Dependency

Scripts

A semantic network or a semantic net is a structure for representing knowledge as a pattern of interconnected nodes and arcs.

Nodes in the semantic net represent either Entities Attributes States or Events

Arcs in the net gives the relationship between the nodes and labels on the arc specify What type of relationship actually exists.

Scooter Two-wheeler

Electrical-system

EngineBrakes

Motor-bike

Moving-vehicle

Fuel-system

Figure-A sample semantic net

Is_a Is_a

has has

has has

Generally, the nodes in the semantic net are classified as:

◦ Generic nodes◦ Individual or Instance nodes

Two-wheeler Moving-vehicle

(a) Generic node

Scooter

Is_a

Two-wheelerIs_a

(b) individual node

Reasoning using semantic networks is an easy task,

All that has to be done is to specify the start node,

From the initial node, other nodes are pursued using the links until the final node is reached.

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A frame can be defined as a data structure that has slots for various objects and a collection of frames consists of expectations for a given situation.

For Exp:-

Air-conditioner StationeryCupboard

ComputerDumb-terminals

PrinterDumb-terminals

Name: Computer Frame

Slots in the frame

Name of the frame

Figure-A sample frame of a computer centre

Declarative Frames

Procedural Frames

Frame that merely contains description about objects is called a declarative/factual/situational frames.

For Exp:-

Air-conditioner StationeryCupboard

ComputerDumb-terminals

PrinterDumb-terminals

Name: Computer Frame

Slots in the frame

Name of the frame

Figure-Declarative frame BACK

Frame that have procedural knowledge embedded in it are called action- procedure frames.

For Exp:-

ExpertExpert

CarburettorCarburettor

ScooterScooter

Remove Carburettor

Remove Carburettor

Clean nozzleClean nozzle

Fix Carburettor

Fix Carburettor

ScooterScooter

Actor

ObjectSource

Destination

Task 1 Task 2 Task 3

Name: Cleaning the jet of Carburettor

Figure- A Procedural frame

Reasoning using frames is done by instantiation.

Instantiation process begins when the given situation is matched with frames that are already in existence.

The reasoning process tries to match the frame with the situation and latter fills up slots for which values must be assigned.

The values assigned to the slots depicts a particular situation and by this, the reasoning process tries to move towards a goal.

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A script is a knowledge representation that is extensivly used for describing stereo- typic sequences of actions.

It is a special case of frame structure.

Scripts tell people what can happen in a situation, what events follow and what role every actor plays.

Scene: Entering the restaurantCustomer enters the restaurantscans the tablesChoose the best oneDecides to sit hereGoes thereOccupies the seat

Scene2: Ordering the foodcustomer asks for menuwaiter brings itCustomer glances itChoose what to eatOrders that item

Scene3: eating the foodWaiter brings the foodCustomer eats it

Scene4: paying the billCustomer asks for the billwaiter brings itCustomer pays for it

Waiter hands the cash to the cashierWaiter brings the balance amountCustomer tips himCustomer moves out of the restaurant

Script: Going to a restaurant

Props: FoodTablesMenuMoney

Roles: OwnerCustomerWaiterCashier

Entry Conditions:

Customer is hungryCustomer has moneyOwner has food

Results:Customer is not hungryOwner has more moneyCustomer has less moneyOwner has less food

Figure- Pseudo-form of a Restaurant Script

Reasoning using scripts is similar to that of frames.

Here also the values of the slots are instantiated.

Advantages:- Permits one to identify what scenes must have been preceded when an

event takes place.

It is possible using scripts to describe each and every event to the minutest detail so that enough light is thrown on implicitly mentioned events.

Scripts provide a natural way of providing a single interpretation from a variety of observations.

Disadvantages:- It is difficult to share knowledge across scripts. What is happening in a script

is true only for that script.

Scripts are designed to represent knowledge in stereo-type situations only and hence can not be generalized.

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Conceptual dependency is a theory of natural language processing which mainly deals with representation of semantics of a language.

The main motivation for the development of CD as a knowledge representation techniques are given below:

To construct computer programs that can understand natural language. To make inferences from the statements and also to identify conditions in

which two sentences can have similar meaning. To provide facilities for the system to take part in dialogues and answer

questions. To provide a necessary plank that sentences in one language can be easily

translated into other languages. To provide a mean of representation which are language independent.

Four Primitive Concept ClassesACTS - Actions

PPs – Objects (Picture producers)

AAs – Modifiers of actions (Action Aiders)

PAs – Modifiers of objects (picture aiders)

Each Action is assumed to reduce to one or more of the primitive ACTs

ATRANS – transfer relationship (give)PTRANS – transfer physical location (go)PROPELMOVEGRASPINGEST

EXPELMTRANSMBUILDCONCSPEAKATTEND

ConceptualDependenc

ySemantics Example

PP ACT An actor acts John PTRANS … John ran

PP PA Object has attribute John height John is tall

ACT O PP Indicates object of action

John Propel O cartJohn pushes the cart

ACT R PP PP

Indicates the receipt And donor of

An Action

John ATRANS R John Mary

John took the book from Mary

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