ID is derived from the word identity, derived from the first two characters in the word. ID is used to distinguish between an entity to another entity. Student ID (SID) is the key differentiator between a student with other students. On the concept of database, the differentiator is unique. SID can be numbers, letters, or a combination of both (alphanumeric). Viewed from the daily context, it is not important to determine which a SID belongs to the type of data. However, when reviewed on database design, determining the type of data, including SID in this case, is important. Problems arise because there is a contradiction between the data type viewed from the data characteristic and practical needs. Type of data for SID is a string, if it is evaluated from the basic concepts and its characteristic. It is acceptable because SID consists of a set of numbers which will not be meaningful if applied arithmetic operations like addition, subtraction, multiplication and division. But in terms of computer organization, data representation type will determine how much data space requirements, speed of access, and speed of operation. By considering the constraints of space and speed on the experiments conducted, SID is better expressed as an integer rather than a set of characters. KEYWORDS aphanumeric,representation, string, integer, space, speed