knowledge representation. what is knowledge representation what is knowledge representation type...
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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.
BACK
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.
BACK
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.
BACK
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
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.
BACK
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.
BACK
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
BACK
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