Alphabet (computer science)

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In computer science, an alphabet is a finite set of characters or digits. The most common alphabet is {0,1}, the binary alphabet. A finite string is a finite sequence of characters from an alphabet; for instance a binary string is a string drawn from the alphabet {0,1}. An infinite sequence of characters may be constructed from elements of an alphabet as well.

Given an alphabet $Σ$ , we write $Σ *$ to denote the set of all finite strings over the alphabet $Σ$ . Here, the $*$ denotes the Kleene star operator. We write $\Sigma^\infty$ (or occasionally, $\Sigma^\N$ or $Σ ω$ ) to denote the set of all infinite sequences over the alphabet $Σ$ .