An identifier is a sequence of one or more alphanumeric characters that uniquely names or characterizes the contents, nature, or properties of: (1) a data element, such as the name of an file, account, procedure, variable, or other such entity, or (2) a label attached to a storage device, such as a hard disk or CD-ROM (Compact Disk-Read-only Memory). Computer systems usually enact rules about identifying (or "naming") objects. For example, there is often a limit to the number of characters that can be used, and not all characters are always allowed.

A data element (from the first definition above) is a fundamental data structure in a data processing system. Any unit of data defined for processing is a data element; for example, "account number," "name," "address," "city," "state," and "zipcode." A data element is defined by size (number of characters) and type (alphanumeric, numeric only, date, etc.). A specific...