Tables
A table is a collection of logically related information treated as a unit. Tables are organized by rows and columns. Figure 1–1 shows the contents of a sample Customer table.
Other common tables include an Order table in a retail database that keeps track of the orders each customer places, an Assignment table in a departmental database that keeps track of all the projects each employee works on, and a Student Schedule in a college database table that keeps track of all the courses each student takes.
Tables are generally grouped into three types—kernels, associations, and characteristics:
- Kernels are tables that are independent entities. They often represent or model things that exist in the real world. Some examples are: customers, vendors, employees, parts, goods, and equipment.
- Associations are tables that represent a relationship among entities. For examples, an order represents an association between a customer and goods.
- Characteristics are tables whose purpose is to qualify or describe some other entity. These tables have no meaning in and of themselves, only in relation to the entity they describe. For example, order-lines might describe orders; without an order, an order-line is useless.