- published: 08 Mar 2014
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In computer science and mathematical logic, an alphabet is a non-empty set of symbols or letters, e.g. characters or digits. For example a common alphabet is {0,1}, the binary alphabet. A finite string is a finite sequence of letters from an alphabet; for instance a binary string is a string drawn from the alphabet {0,1}. An infinite sequence of letters may be constructed from elements of an alphabet as well.
Given an alphabet Failed to parse (Missing texvc executable; please see math/README to configure.): \Sigma , we write Failed to parse (Missing texvc executable; please see math/README to configure.): \Sigma^*
. Here, the Failed to parse (Missing texvc executable; please see math/README to configure.): {}^*
. We write Failed to parse (Missing texvc executable; please see math/README to configure.): \Sigma^\infty
) to denote the set of all infinite sequences over the alphabet Failed to parse (Missing texvc executable; please see math/README to configure.): \Sigma .
For example, if we use the binary alphabet {0,1}, the strings (ε, 0, 1, 00, 01, 10, 11, 000, etc.) would all be in the Kleene closure of the alphabet (where ε represents the empty string)
An alphabet is a standard set of letters (basic written symbols or graphemes) which is used to write one or more languages based on the general principle that the letters represent phonemes (basic significant sounds) of the spoken language. This is in contrast to other types of writing systems, such as logographies, in which each character represents a word, morpheme or semantic unit, and syllabaries, in which each character represents a syllable.
A true alphabet has letters for the vowels of a language as well as the consonants. The first true alphabet is believed to be the Greek alphabet, which is a modified form of the Phoenician alphabet. In other types of alphabet either the vowels are not indicated at all, as was the case in the Phoenician alphabet (such systems are known as abjads), or else the vowels are shown by diacritics or modification of consonants, as in the devanagari used in India and Nepal (these systems are known as abugidas or alphasyllabaries).
There are dozens of alphabets in use today, the most common being the Latin alphabet (which was derived from the Greek). Many languages use modified forms of the Latin alphabet, with additional letters formed using diacritical marks. While most alphabets have letters composed of lines (linear writing), there are also exceptions such as the alphabets used in Braille, fingerspelling, and Morse code.
Computer science or computing science (abbreviated CS or CompSci) designates the scientific and mathematical approach in information technology and its applications, notably computer software and sometimes hardware. A computer scientist is a scientist who specialises in the theory of computation and the design of computers.
Its subfields can be divided into practical techniques for its implementation and application in computer systems and purely theoretical areas. Some, such as computational complexity theory, which studies fundamental properties of computational problems, are highly abstract, while others, such as computer graphics, emphasize real-world applications. Still others focus on the challenges in implementing computations. For example, programming language theory studies approaches to description of computations, while the study of computer programming itself investigates various aspects of the use of programming languages and complex systems, and human-computer interaction focuses on the challenges in making computers and computations useful, usable, and universally accessible to humans.