Knowledge Representation

 What is Knowledge Representation What is Knowledge Representation  Type of knowledge in AI Type of knowledge in AI  Declarative knowledge Declarative knowledge  Procedural Knowledge Procedural Knowledge  Knowledge Representation Schemes Knowledge Representation Schemes  Semantic Networks Semantic Networks  Frames Frames  Scripts Scripts  Conceptual Dependency 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

 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 true else return false end procedure carnivore (x). procedure sharp_teeth (x); if carnivore (x) then return true else 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

 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 Engine Brakes Motor-bike Moving-vehicle Fuel-system Figure-A sample semantic net Is_a 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-wheeler Is_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-conditionerStationery Cupboard Computer Dumb-terminals Printer Dumb-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-conditionerStationery Cupboard Computer Dumb-terminals Printer Dumb-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:- Expert Carburettor Scooter Remove Carburettor Clean nozzle Fix Carburettor Scooter Actor Object Source Destination Task 1Task 2Task 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 restaurant Customer enters the restaurant scans the tables Choose the best one Decides to sit here Goes there Occupies the seat Scene2:Ordering the food customer asks for menu waiter brings it Customer glances it Choose what to eat Orders that item Scene3:eating the food Waiter brings the food Customer eats it Scene4:paying the bill Customer asks for the bill waiter brings it Customer pays for it Waiter hands the cash to the cashier Waiter brings the balance amount Customer tips him Customer moves out of the restaurant Script:Going to a restaurant Props:Food Tables Menu Money Roles:Owner Customer Waiter Cashier Entry Conditions: Customer is hungry Customer has money Owner has food Results: Customer is not hungry Owner has more money Customer has less money Owner 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 Classes ACTS - 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) PROPEL MOVE GRASP INGEST EXPEL MTRANS MBUILD CONC SPEAK ATTEND

Conceptual DependencySemanticsExample PP  ACTAn actor actsJohn  PTRANS … John ran PP  PAObject has attributeJohn  height John is tall ACT  O PPIndicates object of actionJohn  Propel  O cart John 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