Artificial Intelligance Unit-2

Artificial Intelligence Notes

Unit-2

Lecture-1

Knowledge

The underlying thrust force behind every intelligent system is knowledge.

Symbols: Means of representation

Data: Collection of mere symbols

Information: Processed or meaningful data is called information

Knowledge: Knowledge is organized information. One can also define knowledge as a piece of information that helps in decision making.

Intelligence: Intelligence can be defined as the ability to draw useful inferences from the available knowledge.

Wisdom: Wisdom is the maturity of the mind that directs its intelligence to achieve desirable goals.

A human expert has two main types of knowledge:

Ø Domain Specific Knowledge

Ø Common Sense Knowledge

Domain Specific Knowledge:

Domain Specific Knowledge deals with all kinds of knowledge about a particular domain.

There are four types of domain-specific knowledge an expert possesses. They are:-

a) Knowledge about an item or object: This specifies the description & the characteristics of the object.

b) Knowledge about events: For this, the knowledge is stored as a set of procedures.

e.g. What must be the first aid that must be done when a person is rescued while drowning

c) Knowledge about task-performance: Here, the expert possesses knowledge about the capacity of various objects & the limitations of each.

e.g. Anaesthestians decide on which anesthesia & what quantity is to be administered for different patients. This is done based on the capability of the drug and the condition of the patient

d) Knowledge about Knowledge: Also termed as meta-knowledge, this piece of knowledge helps in controlling & planning the reasoning process.

Common-Sense Knowledge:

All other pieces of knowledge that helps in reasoning other than domain-specific knowledge are termed as common-sense knowledge. Common sense knowledge when coupled with domain specific domain specific knowledge increases the performance capability of the system.

Artificial Intelligence Notes

Unit-2

Lecture-2

Knowledge Representation

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

A knowledge representation scheme should provide ways of representing complex knowledge and should posses the following characteristics:-

v The representation scheme should have a set of well defined syntax and semantics. This helps in representing various kinds of knowledge.

v The knowledge representation scheme should have a good expressive capability. A good expressive capability will catalyze the inferencing mechanism in its reasoning process.

v From the computer system point of view, the representation must be efficient. By this we mean that it should use only limited resources without compromising on the expressive power.

Database	Knowledge Base
1. Collection of data representing facts.	1. Has information at a higher level of abstraction.
2. Large volume of data & facts change over time.	2. Significantly smaller than database and changes are gradual.
3. Operates on a single object.	3. Operates on a class of objects rather than a single object.
4. Updates are performed by clerical personnel.	4. Updates are performed by domain experts.
5. All information needed to be explicitly stated.	5. Has the power of inferencing.
6. Maintained for operational purpose.	6. Used for data-analysis & planning.
7. Represented by relational or network or network or hierarchical model.	7. Knowledge representation is by logic or frames or semantic nets.

Declarative Knowledge Representation

A declarative representation declares every piece of knowledge and permits the reasoning system to use the rules of inference like modus ponens, modus tollens etc. to come out with new pieces of information.

For e.g.  “All carnivorous have sharp teeth”,

                “Cheetah is a carnivore”

This can be represented using a declarative representation as:

Carnivore (Cheetah)

Using these two representations, it is possible to deduce that

“Cheetah has sharp teeth”.

This type of representation has the following advantages:

Ø Declarative approaches are flexible

Ø Each piece of knowledge is an independent chunk on its own. Hence modularity is higher.

Ø It is enough that you represent the knowledge only once. To cite, in the above example, the statement

is made only once and the variable x engulfs a wide variety of animals which are carnivorous in nature.

Procedural Knowledge Representation

A procedural representation, on the other hand, represents knowledge as procedures and the inference mechanisms manipulate these procedures to arrive at the result. For e.g. one could write procedure for the above example:

procedure carnivore(x);

             If (x=Cheetah) then return true

             else return false

end procedure carnivore(x)

procedure sharpteeth(x);

              If carnivore(x) then return true

              else return false

end procedure sharpteeth(x)

To see whether cheetah has sharp teeth, one could activate procedure sharpteeth with variable x initiated 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 sharpteeth.

Procedural representation also has many advantages:

Ø Heuristic knowledge can be easily represented which is vital.

Ø One has the control over search which is not available in declarative knowledge representation.

Today, it is agreed that a knowledge representation scheme should have both procedural and declarative schemes for effective organization of the knowledge base.

Artificial Intelligence Notes

Unit-2

Lecture-3

Knowledge Representation Schemes

·        Frames

·        Scripts

·        Semantic Nets

·        First-Order Predicate Logic

·        Conceptual Dependency

·       Fuzzy Logic

Frames

Marvin Minsky in the book on Computer Vision proposed frames as a means of representing common-sense knowledge. In that Minsky proposed that knowledge is organized into small “packets” called frames. The contents of the frame are certain slots which have values. All frames of a given situation constitute the system. Whenever one encounters a situation, a series of related frames are activated and reasoning is done.

“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.”

A Frame structure provides facilities for describing objects, facts about situation, procedures on what to do when a situation is encountered. Because of these facilities a frame provides, frames are used to represent the two types of knowledge, viz., declarative/factual and procedural.

The following is a Frame for a Computer Centre:-

Declarative and Procedural Frames

A frame that merely contains description about objects is called a declarative type/factual/situational frame. The computer centre frame described above is a typical example of this category.

Apart from declarative part in a frame, it is also possible to attach slots which explain how to perform things. In other words, it is possible to have procedural knowledge represented in a frame. Such frames which have procedural knowledge embedded in it are called action-procedure frames. The action-frame has the following slots:-

·        Actor Slot:  which holds information about who is performing the activity.

·        Object Slot: This frame has information about the item to be operated on.

·        Source Slot: Source slot holds information from where the action has to begin.

·        Destination Slot: Holds information about the place where action has to end.

·        Task Slot: This generates the necessary sub-frames required to perform the operation.

Consider a procedural frame for cleaning the jet of a carburetor in a scooter. The generic frame representing this procedural knowledge is given below:

A procedural frame

The generic frame merely describes that, the expert in order to clean the nozzle of the scooter has to merely perform, the following operations:

·        Removing the carburetor from the scooter

·        Opening it up to expose all parts

·        Cleaning the nozzle

·        Refixing it in the scooter

Since the entire operation is done on a scooter, the source and destination slots are the same, viz. the scooter.  For each task slot, it is possible to have other frames (procedural) of how to do it. This is illustrated in the following fig:

Linking of procedural sub-frames

Artificial Intelligence Notes

Unit-2

Lecture-4

Scripts

Frames represented a general knowledge representation structure which can accommodate all kinds of knowledge. Scripts, on the other hand, help exclusively in representing stereo type events that takes place in day-to-day activities. Some such events are:-

·         Going to hotel, eating something, paying the bill and exiting.

·         Going to theatre, getting a ticket, viewing the film/drama and leaving.

·         Going to super market, with a list of items to be purchased, putting items needed on a trolley, paying for them.

·         Leaving home for office in a two-wheeler, parking the two-wheeler at the railway station, boarding the train to the place of work, and going to the place of work.

·         Going to bank for withdrawal, filling the withdrawal slip/cheque, presenting to the cashier, getting money and leaving the bank.

All the situations are stereo-type in nature and specific properties of the restricted domain can be exploited with special purpose structures.

“A Script is a knowledge representation structure that is extensively used for describing stereo-type sequences of actions”.

The following fig. represents a miniature restaurant script with customer going to a restaurant, ordering some eatables, eating them, paying the due amount and leaving the restaurant.

This simple script throws enough light on the important components:

·        Entry Condition: Basic Conditions that must be fulfilled.

·        Result: Presents the situations which describe what happens after the script has occurred.

·        Props: These indicate the objects that are existing in the script.

·        Roles: What various characters play is brought under the slot of roles.

·        Scenes: Sequence of activities are described in detail.

Scripts have some advantages as a knowledge representation structure:

« 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 enough light is thrown on implicitly mentioned events.

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

Despite these advantages, scripts have some drawbacks also:-

« It is difficult to share knowledge across scripts. What is happening in a script is true for that script.

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

Artificial Intelligence Notes

Unit-2

Lecture-5

Logic

One of the prime activities of human intelligence is reasoning. The activity of reasoning involves construction, organization and manipulation of statements to arrive at new conclusions. Thus, logic can be defined as a scientific study of the process of reasoning and the system of rules and procedures that help in the reasoning process.

Basically, the logic process takes in some information (called premises) and produces some outputs (called conclusions).  These laws along with standard formulae help in deriving new information from the existing ones.

Logic is basically classified into two categories:-

1. Propositional Logic

2. Predicate Logic