They are applied wherever exact descriptions of languages are needed: for instance, in official language specifications, in manuals, and in textbooks on programming language theory. His notation to describe Sanskrit word structure notation is equivalent in power to that of Backus and has many similar properties. In the first half of the 20th century, linguists such as Leonard Bloomfield and Zellig Harris started attempts to formalize the form g 1145 pdf of language, including phrase structure. Noam Chomsky, teaching linguistics to students of information theory at MIT, combined linguistics and mathematics by taking what is essentially Thue’s formalism as the basis for the description of the syntax of natural language.
His notation was first used in the ALGOL 60 report. BNF is a notation for Chomsky’s context-free grammars.
Apparently, Backus was familiar with Chomsky’s work. As proposed by Backus, the formula defined “classes” whose names are enclosed in angle brackets.
Each of these names denotes a class of basic symbols. Further development of ALGOL led to ALGOL 60. In the committee’s 1963 report, Peter Naur called Backus’s notation Backus normal form.
Naur form, as it is “not a normal form in the conventional sense”, unlike, for instance, Chomsky normal form. The name Pāṇini Backus form was also once suggested in view of the fact that the expansion Backus normal form may not be accurate, and that Pāṇini had independently developed a similar notation earlier. BNF, as described by Peter Naur in the ALGOL 60 report is metalinguistic formula. Any mark in a formula, which is not a variable or a connective, denotes itself.
Juxtaposition of marks or variables in a formula signifies juxtaposition of the sequence denoted. Another example from the ALGOL 60 report illustrates a major difference between the BNF metalanguage and a Chomsky context-free grammar.
Metalingustic variables do not require a rule defining their formation. The following ALGOL 60 report section 2.