# Terminal Symbol Set

A Terminal Symbol Set is a Formal Alphabet (composed of Terminal Symbol) that is associated to a Formal Grammar.

## References

• http://www.csee.umbc.edu/help/theory/lang_def.shtml
• Alphabet
• A finite set of symbols.
• An alphabet is often denoted by sigma, yet can be given any name.
• B = {0, 1} Says B is an alphabet of two symbols, 0 and 1.
• C = {a, b, c} Says C is an alphabet of three symbols, a, b and c.
• Sometimes space and comma are in an alphabet while other times they are meta symbols used for descriptions.

### 2007

• (Kakkonen, 2007) ⇒ Tuomo Kakkonen. (2007). “Framework and Resources for Natural Language Evaluation." Academic Dissertation. University of Joensuu.
• Definition 3-1. Symbol, terminal and alphabet.
• A symbol is a distinguishable character, such as “a”, “b” or “c”.
• Any permissible sequence of symbols is called a terminal (also referred to as a word).
• A finite, nonempty set ∑ of terminals is called an alphabet.
• Definition 3-2. String and sets of strings.
• Let Σ be an alphabet.
• A finite sequence of symbols S=(x1 x2… xn), n≥0, x∈Σ is called a string in alphabet Σ.
• The length |S| of string S is n.
• The empty string is the sequence of length 0; written ε.
• Σ* is the set of all strings in Σ.
• In addition, Σ+ = Σ*- {ε}.
• Definition 3-3. Language and sentence.
• Let Σ be an alphabet.
• Any subset $\displaystyle{ L }$ of Σ* is called a language over alphabet Σ.
• Sequence δ = (α1 α2 … αn), where αiLi, 1≤in, n' ∈ natural numbers, is called a sentence in language L.