A table is a collection of logically related information treated as a unit. Tables are organized by rows and columns. The following figure shows the contents of a sample Customer table.
Figure 1. Columns and rows in the Customer table
Other common tables include an Order table in a retail database that tracks the orders each customer places, an Assignment table in a departmental database that tracks all the projects each employee works on, and a Student Schedule in a college database table that tracks all the courses each student takes.
Tables are generally grouped into three types:
Kernel tables — Tables that are independent entities. Kernel tables often represent or model things that exist in the real world. Some example kernel tables are customers, vendors, employees, parts, goods, and equipment.
Association tables — Tables that represent a relationship among entities. For example, an order represents an association between a customer and goods.
Characteristic tables — Tables whose purpose is to qualify or describe some other entity. Characteristic only have meaning in relation to the entity they describe. For example, order-lines might describe orders; without an order, an order-line is useless.
Kernel tables — Tables that are independent entities. Kernel tables often represent or model things that exist in the real world. Some example kernel tables are customers, vendors, employees, parts, goods, and equipment.