Formal languages

In computer science, Backus–Naur Form or Backus Normal Form (BNF) is one of the two main notation techniques for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats, instruction sets and communication protocols; the other main technique for writing context-free grammars is the van Wijngaarden form.

In formal language theory, a grammar (when the context is not given, often called a formal grammar for clarity) is a set of production rules for strings in a formal language.

In theoretical computer science and formal language theory, a regular expression (sometimes called a rational expression) is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.

In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable.

A Turing machine is an abstract machine that manipulates symbols on a strip of tape according to a table of rules; to be more exact, it is a mathematical model of computation that defines such a device.

A context-sensitive grammar (CSG) is a formal grammar in which the left-hand sides and right-hand sides of any production rules may be surrounded by a context of terminal and nonterminal symbols.

A two-level grammar is a formal grammar that is used to generate another formal grammar , such as one with an infinite rule set .

In computer science, an abstract syntax tree (AST), or just syntax tree, is a tree representation of the abstract syntactic structure of source code written in a programming language.

A metacharacter is a character that has a special meaning (instead of a literal meaning) to a computer program, such as a shell interpreter or a regular expression engine.

A production or production rule in computer science is a rewrite rule specifying a symbol substitution that can be recursively performed to generate new symbol sequences.

In mathematical logic and theoretical computer science, an abstract rewriting system (also (abstract) reduction system or abstract rewrite system; abbreviation ARS) is a formalism that captures the quintessential notion and properties of rewriting systems.

According to Rudolf Carnap, in logic, an interpretation is a descriptive interpretation (also called a factual interpretation) if at least one of the undefined symbols of its formal system becomes, in the interpretation, a descriptive sign (i.e., the name of single objects, or observable properties).

A tell-tale or telltale is an indicator, signal, or sign that conveys the status of a situation, mechanism, or system.

In a formal grammar, an erasing rule is a rule which maps a string of symbols to the empty string (ε).

A simple precedence grammar is a context-free formal grammar that can be parsed with a simple precedence parser.

In mathematics, an antimatroid is a formal system that describes processes in which a set is built up by including elements one at a time, and in which an element, once available for inclusion, remains available until it is included.