meljun cortes programming languages logic programming

8/8/2019 MELJUN CORTES Programming Languages Logic Programming

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Logic Programming

Programming Languages

* Property of STI

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Logic Programming

The term logic programming refers looselyto:

The use of facts and rules to representinformation, and

The use of deduction to answer queries.

These two aspects reflect a division of labor between programmers and the language for

logic programming.

Programmers supply the facts and rules,and the language uses deduction tocomputer answers and queries.


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Logic Programming


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Logic Programming

Predicate calculus includes a wider rangeof entities.

It permits the description of relations andthe use of variables.

Formal logic is presented using

propositions and symbolic logic. Propositions is defined as a logical statement

that may or may not be true.

Symbolic logic is used to expresspropositions, relationships betweenpropositions, and how new propositions can

be inferred from existing ones that are true.


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Logic Programming


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Propositions Two basic elements of logic programming

propositions:

A constant is an object that retains its valuethroughout the execution of a program

A variable is an object used to representdata that can be changed while the programor procedure is running.• Different from variables in imperative

languages

tomic propositionsconsist of compound

terms Compound term is one element of a

mathematical relation, written like amathematical function• Functor is a function symbol that names the

relationship

• Ordered list of parameters (tuple)

Example:

male (francis)

like (john,jane)

man (ian)


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Logic Programming


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Propositions

List of connectors used in predicatecalculus

Precedence proceeds top-down

Name Symbol Example Meaning

negation a not a

conjunction a b a and b

disjunctiona b

a or bequivalence = a b a is

equivalentto b

implication a b a implies b

implication a b b implies a


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Logic Programming


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Propositions

Clausal Form

Too many ways to state the same thing

Use a standard form for propositions

B1 B2 … Bn A 1 A 2 … A m• means if all the As are true, then at least one

B is true

• Antecedent: right side

• Consequent: left side

Example:

if it is raining and it is windy, then there is atyphoon

if there is a typhoon, then it is raining and itis windy


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Basic Elements of

PROLOG

Terms

collection of statements that can be a

constant, a variable, or a structure Example:

terms_s

‘term’

12

‘number_12’

Variables are strings of letters, digits andunderscores that begin with an uppercaseletter

• Example:

Number_17

Variable

Structures are PROLOG equivalent of atomicpropositions in predicate calculus

• Example:

female (anna).

taste (lemon, sour).

predecessor (mary, shelley) :-

mother(mary, shelley.).


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Basic Elements of

PROLOG

Fact Statements

building blocks of logic programming

the bases to which a given hypothesis isderived

Example:

female (anna).

taste (lemon, sour).

Rule Statements

commonly known as headed Horn clauses

syntax:

consequence_1:- antecedent_expression

Goal Statements

syntactic form of Prolog that is identical toheadless Horn clauses

Example:

man(jose)

father(X, juan)


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Basic Elements of

PROLOG

Data types are set of values and someoperations that can be performed on that

set of values.

Simple types are implementationsdependent in PROLOG – theseimplementations are summarized in thefollowing table.

Composite types are composed of basictypes.

• In Prolog, a list is designated by square brackets [ ]

•

Example: [dog,act,mouse]

TYPE V LUES

boolean true, fail

integer integers

real floating point numbers

variable variables

atom character sequences


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Basic Elements of

PROLOG

Type Predicates

• The following built-in predicates are used to

determine the type of a parameter:

Predicate CHECKS IF

var (V) V is a variable

nonvar (NV) NV is not a variable

atom (A) A is an atominteger (I) I is an integer

real (R) R is a floating point number

number (N) N is an integer or real

atomic (A) A is an atom or a number

functor (T,F,A) T is a term with functor F andarity A

T = ..L T is a term, L is a list

clause(H,T) H :- T is a rule in the program


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Basic Elements of

PROLOG

rithmetic Expressions

evaluated using the built-in predicate “is”

that is used as an infix operator in thefollowing form:

variable is expression

rithmetic Operations

PROLOG provides standard arithmeticexpressions as summarized in the table:

SYMBOL OPER TION

+ addition

- subtraction

* multiplication

/ real division

// integer division

Mod modulus

** power


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Basic Elements of

PROLOG

Boolean Predicates

Prolog provides more general comparison

operators that compare terms andpredicates to test for unifiability and

whether terms are identical.

SYMBOL OPER TION CTION COMMENTS

A ?= B Unifiable A and B are

unifiable but

Does not

unify A andB

A = B Unify Unify A andB if possible

A \+= B Not unifiable

A == B Identical Does notunify A and

B

A \+== B Not identical

A =:= B Equal (value) Evaluates Aand B to

Determine ifequal

A =\+= B less than(numeric)


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Basic Elements of

PROLOG

SYMBOL OPER TION CTION COMMENTS

A < B Less or equal(numeric)

A =< B Greater than(numeric)

A > B Greater orequal(numeric)

A >= B Less than(terms)

A @< B Less or equal(terms)

A @=< B Less or equal(terms)

A @> B Greater than(terms)

A @>= B Greater orequal (terms)

Continuation..


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Basic Elements of

PROLOG

Logical Operators

Predicates are functions that return a

Boolean value. Thus, the logical operatorsare built into the language.

The table below summarizes the logicaloperators:

SYMBOL OPER TION

not negation

\+ not provable

, logical conjunction

; logical disjunction

:- logical implication

-> if-then-else


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Applications of Logic

Programming

Relational Database Management Systems

simple tables of information can be

described by Prolog rules

Expert Systems

consist of a database of facts, an inferencingprocess, some heuristics about the domain,and some friendly human interface

Natural Language Processing

natural language itself is a grammar in itselfalbeit possesses com inherent redundanciesand ambiguity

meljun cortes programming languages logic programming

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