Types of Knowledge Representation

Types of Knowledge Representation

Knowledge can be represented in different ways. The structuring of knowledge and how designers might view it, as well as the type of structures used internally are considered. Different knowledge representation techniques are

a.     Logic

b.     Semantic Network

c.      Frame

d.     Conceptual Graphs

e.      Conceptual Dependency

f.       Script

Logic

A logic is a formal language, with precisely defined syntax and semantics, which supports sound inference. Different logics exist, which allow you to represent different kinds of things, and which allow more or less efficient inference. The logic may be different types like propositional logic, predicate logic, temporal logic, description logic etc. But representing something in logic may not be very natural and inferences may not be efficient.

Semantic Network

A semantic network is a graphical knowledge representation technique. This knowledge representation system is primarily on network structure. The semantic networks were basically developed to model human memory. A semantic net consists of nodes connected by arcs. The arcs are defined in a variety of ways, depending upon the kind of knowledge being represented.

The main idea behind semantic net is that the meaning of a concept comes, from the ways in which it is connected to other concepts. The semantic network consists of different nodes and arcs. Each node should contain the information about objects and each arc should contain the relationship between objects. Semantic nets are used to find relationships among objects by spreading activation about from each of two nodes and seeing where the activation met this process is called intersection search.

For example: Ram is a boy.

Semantic network by using Instances

The semantic network based knowledge representation mechanism is useful where an object or concept is associated with many attributes and where relationships between objects are important. Semantic nets have also been used in natural language research to represent complex sentences expressed in English. The semantic representation is useful because it provides a standard way of analyzing the meaning of sentence. It is a natural way to represent relationships that would appear as ground instances of binary predicates in predicate logic. In this case we can create one instance of each object. In instance based semantic net representations some keywords are used like: IS A, INSTANCE, AGENT, HAS-PARTS etc.

Consider the following examples:

1. Suppose we have to represent the sentence “Sima is a girl”.

2. Ram is taller than Hari

3.    “Mouse is a Rodent and Rodent is a mammal. Mouse ha s teeth and etas grass”. Check whether the sentence mammal has teeth is valid or not. ]

Partitioned Semantic Network

Some complex sentences are there which cannot be represented by simple semantic nets and for this we have to follow the technique partitioned semantic networks. Partitioned semantic net allow for

1.     Propositions to be made without commitment to truth.

2.     Expressions to be quantified.

In partitioned semantic network, the network is broken into spaces which consist of groups of nodes and arcs and regard each space as a node.

Let us consider few examples.

Draw the partitioned semantic network structure for the followings:

a)       Sima is eating an apple.

b) All Sima are eating an apple.

c) All Sima are eating some apple.

d) All men are mortal

e)                 Every dog has bitten a shopkeeper

f)                  Every dog in town has bitten a shopkeeper.

NOTE: On the above semantic network structures, the instance “IS A” is used. Also two terms like assailant and victim are used. Assailant means “by which the work is done” and that of victim refers t o “on which the work is applied”. Another term namely GS, which refers to General Statement. For GS, make a node g which is an instance of Gs. Every element will have at least two attributes. Firstly, a form that states which a relation is being asserted. Secondly, one or more for all (") or there exists ($) connections which represent universally quantifiable variables.

FRAME

A frame is a collection of attributes and associated values that describe some entity in the world. Frames are general record like structures which consist of a collection of slots and slot values. The slots may be of any size and type. Slots typically have names and values or subfields called facets. Facets may also have names and any number of values. A frame may have any number of slots, a slot may have any number of facets, each with any number of values. A slot contains information such as attribute value pairs, default values, condition for filling a slot, pointers to other related frames and procedures that are activated when needed for different purposes. Sometimes a frame describes an entity in some absolute sense, sometimes it represents the entity from a particular point of view. A single frame taken alone is rarely useful. We build frame systems out of collection of frames that are connected to each other by virtue of the fact that the value of an attribute of one frame may be another frame. Each frame should start with an open parenthesis and closed with a closed parenthesis.

Syntax of a frame

Let us consider the below examples.

1) Create a frame of the person Ram who is a doctor. He is of 40. His wife name is Sita. They have two children Babu and Gita. They live in 100 kps street in the city of Delhi in India. The zip code is 756005.

(Ram

(PROFESSION (VALUE Doctor))

(AGE (VALUE 40))

(WIFE (VALUE Sita))

(CHILDREN (VALUE Bubu, Gita))

(ADDRESS

(STREET (VALUE 100 kps))

(CITY(VALUE Delhi))

(COUNTRY(VALUE India))

(ZIP (VALUE 756005))))

2) Create a frame of the person Anand who is a chemistry professor in RD Women’s College. His wife name is Sangita having two children Rupa and Shipa.

(Anand

(PROFESSION (VALUE Chemistry Professor))

(ADDRESS (VALUE RD Women’s College))

(WIFE (VALUE Sangita))

(CHILDREN(VALUE RupaShipa)))

3) Create a frame of the person Akash who has a white maruti car of LX-400 Model. It has 5 doors. Its weight is 225kg, capacity is 8, and mileage is 15 km /lit.

(Akash

(CAR (VALUE Maruti))

(COLOUR (VALUE White))

(MODEL (VALUE LX-400))

(DOOR (VALUE 5))

(WEIGHT (VALUE 225kg))

(CAPACITY (VALUE 8))

(MILAGE (VALUE 15km/lit)))

The frames can be attached with another frame and can create a network of frames. The main task of action frame is to provide the facility for procedural attachment and help in reasoning process. 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 current problem state with the frame slot and assigns them values.The valuesassigned to the slots depict a particular situation and by this, the reasoning process moves towards a goal. The reasoning process can be defined as filling slot values in frames.

Conceptual Graphs

It is a knowledge representation technique which consists of basic concepts and the relationship between them. As the name indicates, it tries to capture the concepts about the events and represents them in the form of a graph. A concept may be individual or generic. An individual concept has a type field followed by a reference field. For example person : Ram. Here person indicates type and Ram indicates reference.

An individual concept should be represented within a rectangle in graphical representation and within a square bracket in linear representation. The generic concept should be represented within an oval in graphical representation and within a parenthesis in linear representation. Conceptual graph is a basic building block for associative network. Concepts like AGENT, OBJECT, INSTRUMENT, PART are obtained from a collection of standard concepts. New concepts and relations can be defined from these basic ones. These are also basic building block for associative network. A linear conceptual graph is an elementary form of this structure. A single conceptual graph is roughly equivalent to a graphical diagram of a natural language sentence where the words are depicted as concepts and relationships.

Consider an example

“Ram is eating an apple “

Conceptual Dependency

It is an another knowledge representation technique in which we can represent any kind of knowledge. It is based on the use of a limited number of primitive concepts and rules of formation to represent any natural language statement. Conceptual dependency theory is based on the use of knowledge representation methodology was primarily developed to understand and represent natural language structures. The conceptual dependency structures were originally developed by Roger C SChank in 1977.

If a computer program is to be developed that can understand wide phenomenon represented by natural languages, the knowledge representation should be powerful enough to represent these concepts. The conceptual dependency representation captures maximum concepts to provide canonical form of meaning of sentences. Generally there are four primitives from which the conceptual dependency structure can be described. They are

a.       ACTS         : Actions

b.       PPs    : Objects (Picture Producers)

c.       AAs  : Modifiers of Actions (Action Aiders)

d.       Pas    : Modifiers of PPs (Picture Aiders)  

e.       TS     : Time of action   

Conceptual dependency provides both a structure and a specific set of primitives at a particular level of granularity, out of which representation of particular pieces of information can be constructed.

For example

Where ←: Direction of dependency

Double arrow indicates two way link between actor and action.

P: Past Tense

ATRANS: One of the primitive acts used by the theory

O: The objective case relation

R: Recipient case Relation

In CD, representation of actions are built from a set of primitive acts.

1)    ATRANS: Transfer of an abstract relationship (give, accept, take)

2)    PTRANS: Transfer the physical location of an object ( Go, Come, Run, Walk)

3)    MTRANS: Transfer the mental information (Tell)

4)    PROPEL: Application of physical force to an object (push, pull, throw)

5)    MOVE: Movement of a body part by its owner (kick).

6)    GRASP: Grasping of an object by an action (clutch)

7)    INGEST: Ingestion of an object by an animal (eat)

8)    EXPEL: Expel from an animal body (cry)

9)    MBUILD: Building new information out of old (decide)

10)                SPEAK: Production of sounds (say)

ATTEND: Focusing of a sense organ towards a stimulus (Listen)

The main goal of CD representation is to capture the implicit concept of a sentence and make it explicit. In normal representation of the concepts, besides actor and object, other concepts of time, location, source and destination are also mentioned. Following conceptual tenses are used in CD representation.

1)      O: Object case relationship

2)      R: Recipient case relationship

3)      P       : Past

4)      F       : Future

5)      Nil     : Present

6)      T       : Transition

7)      Ts      : Start Transition

8)      Tf      : Finisher Transition

9)      K       : Continuing

10)    ?        : Interrogative

11)    /         : Negative

12)    C       : Conditional

SCRIPT

It is an another knowledge representation technique. Scripts are frame like structures used to represent commonly occurring experiences such as going to restaurant, visiting a doctor. A script is a structure that describes a stereotyped sequence of events in a particular context. A script consist of a set of slots. Associated with each slot may be some information about what kinds of values it may contain as well as a default value to be used if no other information is available. Scripts are useful because in the real world, there are no patterns to the occurrence of events. These patterns arise because of clausal relationships between events. The events described in a script form a giant casual chain. The beginning of the chain is the set of entry conditions which enable the first events of the script to occur. The end of the chain is the set of results which may enable later events to occur. The headers of a script can all serve as indicators that the script should be activated.

Once a script has been activated, there are a variety of ways in which it can be useful in interpreting a particular situation. A script has the ability to predict events that has not explicitly been observed. An important use of scripts is to provide a way of building a single coherent interpretation from a collection of observation. Scripts are less general structures than are frames and so are not suitable for representing all kinds of knowledge. Scripts are very useful for representing the specific kinds of knowledge for which they were designed.

A script has various components like:

1)    Entry condition: It must be true before the events described in the script can occur. E.g. in a restaurant script the entry condition must be the customer should be hungry and the customer has money.

2)    Tracks: It specifies particular position of the script e.g. In a supermarket script the tracks may be cloth gallery, cosmetics gallery etc.

3)    Result: It must be satisfied or true after the events described in the script have occurred. e.g. In a restaurant script the result must be true if the customer is pleased. The customer has less money.

4)    Probs: It describes the inactive or dead participants in the script e.g. In a supermarket script, the probes may be clothes, sticks, doors, tables, bills etc.

5)      Roles: It specifies the various stages of the script. E.g. In a restaurant script the scenes may be entering, ordering etc.

Now let us look on a movie script description according to the above component.

a)       Script name          : Movie

b)      Track : CINEMA HALL

c)       Roles : Customer(c), Ticket seller(TS), Ticket Checker(TC), Snacks

                   Sellers (SS)

d)      Probes        : Ticket, snacks, chair, money, Ticket, chart

e)       Entry condition    : The customer has money

                   The customer has interest to watch movie.

6)      Scenes:

a.       SCENE-1 (Entering into the cinema hall)

CPTRANS C into the cinema hall

C ATTEND eyes towards the ticket counter C PTRANS C towards the ticket counters C ATTEND eyes to the ticket chart

C MBUILD to take which class ticket C MTRANS TS for ticket

C       ATRANS money to TS

TS     ATRANS ticket to C

b.       SCENE-2 (Entering into the main ticket check gate)

C PTRANS C into the queue of the gate C ATRANS ticket to TC

TC     ATTEND eyes onto the ticket

TC     MBUILD to give permission to C for entering into the hall

TC     ATRANS ticket to C

C       PTRANS C into the picture hall.

c.     SCENE-3 (Entering into the picture hall)

CATTEND eyes into the chair

TC    SPEAK where to sit

C                 PTRANS C towards the sitting position

C                 ATTEND eyes onto the screen d. SCENE-4 (Ordering snacks)

C                 MTRANS SS for snacks

SS            ATRANS snacks to C

C                 ATRANS money to SS

C                 INGEST snacks e. SCENE-5 (Exit)

C                   ATTEND eyes onto the screen till the end of picture

C       MBUILD when to go out of the hall

C       PTRANS C out of the hall

7)    Result:

The customer is happy

The customer has less money

Example 2: Write a script of visiting a doctor in a hospital

1) SCRIPT_NAME : Visiting a doctor

2) TRACKS : Ent specialist

3) ROLES : Attendant (A), Nurse(N), Chemist (C), Gatekeeper(G), Counter clerk(CC), Receptionist(R), Patient(P), Ent specialist Doctor (D), Medicine Seller (M).

4) PROBES : Money, Prescription, Medicine, Sitting chair, Doctor’s table, Thermometer, Stetho scope, writing pad, pen, torch, stature.

5) ENTRY CONDITION: The patient need consultation. Doctor’s visiting time on.

6)    SCENES:

a.  SCENE-1 (Entering into the hospital)

PPTRANS P into hospital

P                  ATTEND eyes towards ENT department

P                  PTRANS P into ENT department

P                  PTRANS P towards the sitting chair b. SCENE-2 (Entering into the Doctor’s Room)

P                  PTRANS P into doctor’s room

P                  MTRANS P about the diseases

P                  SPEAK D about the disease

D                 MTRANS P for blood test, urine test

D                 ATRANS prescription to P

P                  PTRANS prescription to P.

P                  PTRANS P for blood and urine test c. SCENE-3 (Entering into the Test Lab)

P                  PTRANS P into the test room

P                  ATRANS blood sample at collection room

P                  ATRANS urine sample at collection room

P ATRANS the examination reports

d.  SCENE-4 (Entering to the Doctor’s room with Test reports)

P                  ATRANS the report to D

D      ATTEND eyes into the report

D      MBUILD to give the medicines

D      SPEAK details about the medicine to P

P       ATRANS doctor’s fee

P                  PTRANS from doctor’s room

e.   SCENE-5 (Entering towards medicine shop)

P                  PTRANS P towards medicine counter

P       ATRANS Prescription to M

M      ATTEND eyes into the prescription

M      MBUILD which medicine to give

M      ATRANS medicines to P

P       ATRANS money to M

P                  PTRANS P from the medicine shop

7)    RESULT:

The patient has less money

Patient has prescription and medicine.

Advantages And Disadvantages Of Different Knowledge Representation