7. ENTITY RELATIONSHIP MODELLING
7.3.1: Atomic Attributes
A simple, or atomic, attribute is one that cannot be decomposed into meaningful components. For example, consider an attribute for gender – such an attribute will assume values such as Male or Female. Gender cannot be meaningfully decomposed into other smaller components.
As another example consider an attribute for product price. A sample value for product price is $21.03. Of course, one could decompose this into two attributes where one attribute represents the dollar component (21), and the other attribute represents the cents component (03), but our assumption here is that such decompositions are not meaningful to the intended application or system. So, we would consider product price to be atomic because it cannot be usefully decomposed into meaningful components.
Similarly, an attribute for the employee’s last name cannot be decomposed, because you cannot subdivide last name into a finer set of meaningful attributes.
Exercises
1) Consider that a Human Resources system must keep track of employees. If we are only including atomic attributes, what attributes would you include for the employee’s name? Some possibilities are first name, last name, middle name, full name.
2) What simple attributes are used to describe courses at your institution?
3) In some large organizations where there are several buildings and floors we see room numbers that encode information about the building, floor, and room number. For example, in case the room 3C13 stands for room 13 on the third floor of the Centennial building. Suppose we need to include Room in an ERD. How would you represent the room number given that you must include atomic attributes only?
