Intelligent Control Methods

Lecture 7: Knowledge representation

Slovak University of TechnologyFaculty of Material Science and Technology in Trnava

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The quality of AI-system is determined by used knowledge.

The knowledge is explicit formulated and stored in system (exception: NN and GA)

Knowledge representation: Formulation of knowledge in the symbolic form (so that they can be effective stored, manipulated and exploited)

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Knowledge representation schemes:

The scheme determines the way of knowledge organization in system. The manner of knowledge manipulation is by the scheme determined, too (but not single-valued).

Used schemas: declarative production rules frames associative nets procedural

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Declarative representation

Knowledge is given (declared) as description of discrete states of problem environment description of possible changes of states to another

states (operators)

Description is separated from solution process Solution methods: resolution method, searching

in state space, GPS, STRIPS, ... Typical representative: predicate calculus of the

1st order

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Predicate calculus (example of declarative knowledge representation)

The base element is a predicate (fact about an object or about relationship between objects; in case of object concretization the predicate = statement (preposition)). P(x) – x is tall (or x wears hat, ...) L(x,y) – x > y (or x loves y) – according to interpretation

Knowledge is formulated like logical expression consisting of quantifiers, predicates and logical operators: (x,y,z): parent(x,y) parent(y,z) man(x) grandfather(x,z)

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Declarative representation Advantages:

simplicity theoretical background good connection to solving methods

Disadvantages: without time and qualitative changes without quantitative information (4 from 5, for more

then 10 ... ) without uncertainty (only yes - no) the complexity of solution grows exponential with

formulas number

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Production rules

the most used schema Form:

IF antecedent THEN consequent IF assumption THEN conclusion (declarative interpretation) IF condition THEN action (procedural interpretation)

Antecedent is 1 or more assertions, connected by logical operations. Consequent is a fact or an action. If the liquid is white, then the liquid is milk. If the liquid is white, then it is necessary to call firemen.

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Production rules - chaining

Consequent in 1 rule can be antecedent in another one – rules are chained.

R1: If the patient worked before 1985 like tiler (A1)then the patient worked with asbestos. (C1)

R2: If the patient worked with asbestos (A2)and the patient worked in closed spaces (A3)then his lungs contain asbestos dust. (C2)

A1 C1=A2

A3

C2

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Production rules

Chained rules create graph (tree). Solving methods:

forward chaining (new facts deduction till the goal fact is derived)

backward chaining (verification of the goal fact truth by verification its antecedent)

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Production rules

Advantages: simple creationsimple supplement (to the width, to the

depth))simple modificationsimple inference

Disadvantages: ineffective inferencediffer from human knowledge

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Frames

Minsky 1975, beginning of OOP. The frame is a structure, which represents

some stereotypic situation. blank (form) with couples (columns) attribute -

valueEmpty: prototype frameWith at least one completed value: frame

instance

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Frames

Rubriky:hodnota instruction for value determination (function)default inherent value frame

Task solution: Value determination in some column.

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Semantic nets

Oriented graphs nodes – objects, concepts, actions, ... arcs – relations

STU belongs to MTF Trnava seats MTF

Trnava seats MTF

belongs to

STU

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Semantic nets: Solution

Knowledge:

Trnava seats MTF

belongs to

STU

Task (problem): To what does MTF belong?

X belongs to MTF

Knowledge:

Trnava seats MtF

belongs to

STU X=STU

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Semantic nets

difficulties with logical operations representation

difficult quantification used by memory modeling and by natural

language analysis

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Procedural representation Knowledge in form of procedures description not important (what is it), but the way

of manipulation (how) the solution means the steps sequence to

answer (algorithm) typical for procedural („ordinary“) programming

languages In AI: Automatic procedures call in PROLOG

and PLANNER