An identifier is a unique expression in a written format either by a code, by numbers or by the combination of both to distinguish variations from one to another among a class of substances, items, or objects. For living organisms and the structural identifications of objects, identifiers could be more complicated. In computer science, Identifiers (IDs) are lexical tokens that name entities. The concept is analogous to that of a "name." Identifiers are used extensively in virtually all information processing systems. Naming entities makes it possible to refer to them, which is essential for any kind of symbolic processing.