the backus naur form-oct19

8/20/2019 The Backus Naur Form-oct19

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The Backus Naur

Form


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Metalanguage

Language that describes other languages


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Parts of a Description of a

Language Syntax Semantics


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Syntax

Set of rules that determines which constructs

are correctly formed programs and which are

not


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Semantics

Description of the way a syntactically correct

program is interpreted or carried our

eg. A:=B;


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Backus Naur Form

A metalanguage that is used to describe the syntax A formal notation for specifying programming

language

t was presented by !ohn Bac"us at an internationalconference in #$%$ &as later slightly modified by 'eter (aur for the

description of Algol )*

t soon became the most popular method ofconcisely describing programming language syntax t was parallel to the study of "nown linguist (oam

+homs"y


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JON B!"#$S

#$,- raduated from /ill school 'ottstown

#$,- 0ntered the 1ni2ersity of 3irginia. !oined the army

#$,% 0ntered 4lower and 4ifth A2enue 5edical School in (ew 6or" #$,$ &or"ed on B57S SS0+ computer

#$%*8#$%- &atson Lab

#$%, Bac"us and his team publish 4ortran

#$%$ De2elopng a notation called Bac"us8(aur 4orm in

collaboration with (aur

#$$# 9etirement

ctober -< #$$ in the 1+LA 5edical +enter at the age of

+hronology


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JON B!"#$S

#$) 9ecei2es (ational medal of Science

#$ recei2ed the A+5 >uring Award Lecture.?-@

#$$ 9ecei2ed doctor honoris causa of the 1ni2ersit /enri'oincar 8 (ancy< 4rance< on December #, #$$.?,@

#$$ 9ecei2es +harles Star" Draper price for his wor" on 4ortran

#$$ 4ellow Award 9ecipient of the +omputer /istory 5useum for

his de2elopment of 49>9A(< contributions to computer systems

theory and software proCect management.

Honors and Awards

http://www.thocp.net/biographies/backus_john.htm#Metalanguagehttp://www.thocp.net/biographies/backus_john.htm#Syntaxhttp://www.thocp.net/biographies/backus_john.htm#Syntaxhttp://www.strep-necst.org/article.php3?id_article=10http://www.thocp.net/biographies/backus_john.htm#Metalanguage


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One %eal &orl' (xample)

The (nglish Language*rammar


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(lements of the BNF

Notation Set of >erminal Symbols Set of (on8>erminal Symbols

Set of 'roduction 9ules

oalbCecti2e


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Set of Terminal Sym+ols

Atomic or non8di2isible symbols that can be

combined to form 2alid constructs in the

language

1sually set of characters though some

language may consider certain character

string to be symbols


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Set of Non,Terminal Sym+ols

Symbols which are not included in the

language itself but are symbols used to

represent intermediate definitions within the

language as defined by the production rules 9epresents syntactic classes or categories


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Set of Pro'uction %ules

A definition of a non8terminal symbol

format:

E 6

where E is a nonterminal symbol

6 is a seFuence of symbols each of

which can be either >erminalor (on8terminal


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*oal Sym+ol

Start symbol


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%ules in Forming *rammars

#. 02ery (onterminal symbol must appear to

the left of the of at least one ?#@

production rule

-. oal symbol must not appear to the right ofthe of any productions


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T-o &ays of $sing a*rammar#. >o generate 2alid programs of a language

-. 9eduction of a program


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>/0 +AL+1LA>9 LA(1A0


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"S (NT%. / 012 pointseach3#. &hat happens if grammar is not present in a

natural languageG

-. &hat is the importance of a grammar in a

natural languageG. &hat is the implication if we only ha2e one

grammar in programmingG


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(xten'e' Backus,Naur Form0(BNF3 Additional >hree symbols:

H Alternation

I J ptional

K 9epetition


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The !lternation Sym+ol 4

use of the or symbol to express alternate

definition for the same non8terminal symbol

within the single production rule

eg. dd #

dd

dd %


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The Optional Sym+ol

9epresents an optional item

Mero or one occurrence of the symbol

eg. E 6 I M J


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The %epetition Sym+ol 5 6

Specifies repeated item

eg. E 6 K6


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!lpha+et, !

Any single symbol from the "eyboard

the backus naur form-oct19

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