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Introduction

In this section you will learn the basic definitions.

Language

The first basic definition you need to know is the language.

Language is an organized system of signs,symbols and rules.

There are two types of languages:

  • Natural language
  • Formal language

Natural language may refer either to the specifically human capacity for acquiring and using complex systems of communication,or to a specific instance of such a system of complex communication. Natural language can be based on visual rather than auditive stimuli,for example in sign languages and written language.

Natural language is created spontaneous and evolutionary. It is hard to define this language.

Formal language is a set of words,i.e. finite strings of letters,symbols or tokens. In computer science they are used for the precise definition of data formats and the syntax of programming languages.

Rules of artificial languages ​​are defined before their use. These languages ​​are pre-planned and can be defined exactly.

Elements of language

There are three elements of language:

  • syntax
  • semantics
  • pragmatics

Syntax is the study of the principles and rules for constructing sentences in natural languages.

Semantics is the study of meaning. It focuses on the relation between signifiers ,such as words,phrases,signs and symbols,and what they stand for,their denotata. Linguistic semantics is the study of meaning that is used by humans to express themselves through language. Other forms of semantics include the semantics of programming languages,formal logics,and semitoics.

Pragmatics is a subfield of linguistics which studies the ways in which context contributes to meaning. It studies how the transmission of meaning depends not only on the linguistic knowledge of the speaker and listener,but also on the context of the utterance,knowledge about the status of those involved,the inferred intent of the speaker.

 

Interesting…

Methods for defining syntax:

  • generative grammar
  • categorial grammar
  • dependency grammar

Metalanguage

It is impossible to describe the language of his own words so you need metalanguage.

Metalanguage is language or symbols used when language itself is being discussed or examined. Expressions in a metalanguage are often distinguished from those in an object language by the use of italics,quotation marks,or written on a separate line.

Types of metalanguage

There are a variety of recognized metalanguages:

  • embedded metalanguage
  • ordered metalanguage
  • nested (hierarchical) metalanguage

Expressions in a metalanguage:

There are several entities commonly expressed in a metalanguage. In logic usually the object language that the metalanguage is discussing is a formal language,and very often the metalanguage as well.

  • deductive systems
  • metavariables
  • metatheories and metatheorems
  • interpretations

Backus Normal Form

BNF (Backus Normal Form or Backus–Naur Form) is a notation technique for contex-free grammars,often used to describe the syntax of languages used in computing,such as computer programmingd languages,document formats,instruction sets and communication protocols. It is applied wherever exact descriptions of languages are needed,for instance,in official language specifications,in manuals,and in textbooks on programming language theory.

A BNF specification is a set of derivation rules,written as

 <symbol>::= <expression>

Po lewej stronie występuje pojedynczy symbol nieterminalny,natomiast po prawej ciąg symboli nieterminalnych i terminalnych.

Example

<postal-address>::= <name-part><street-address><zip-part>
<name-part>::= <personal-part><last-name><opt-jr-part><EOL>
| <personal-part><name-part><EOL>
<personal-part>::= <first-name>| <initial>"."
<street-address>::= <house-num><street-name><opt-apt-num><EOL>
<zip-part>::= <town-name>"," <state-code><ZIP-code><EOL>
<opt-jr-part>::= "Sr." | "Jr." | <roman-numeral>| ""

Interesting…

BNF notation was introduced by John Backus work on the Fortran language,and later more widely used by Peter Naur to define the syntax of the language Algol.

Questions

  • Are we able to define all the sentences correctly for a natural language?
  • Is it possible to define a language using the words contained in it?
  • Does every sentence have  only one possible notation in the BNF?

If you do not know the answer to these questions,read again the above content.