Practical examples of data modeling

To better understand the key activities that are necessary for creating valid data models, investigate one or more real-life data modeling scenarios.

You begin by defining your entities, the significant objects of interest. Entities are the things about which you want to store information. For example, you might want to define an entity, called EMPLOYEE, for employees because you need to store information about everyone who works for your organization. You might also define an entity, called DEPARTMENT, for departments.

Next, you define primary keys for your entities. A primary key is a unique identifier for an entity. In the case of the EMPLOYEE entity, you probably need to store a large amount of information. However, most of this information (such as gender, birth date, address, and hire date) would not be a good choice for the primary key. In this case, you could choose a unique employee ID or number (EMPLOYEE_NUMBER) as the primary key. In the case of the DEPARTMENT entity, you could use a unique department number (DEPARTMENT_NUMBER) as the primary key.

After you have decided on the entities and their primary keys, you can define the relationships that exist between the entities. The relationships are based on the primary keys. If you have an entity for EMPLOYEE and another entity for DEPARTMENT, the relationship that exists is that employees are assigned to departments. You can read more about this topic in the next section.

After defining the entities, their primary keys, and their relationships, you can define additional attributes for the entities. In the case of the EMPLOYEE entity, you might define the following additional attributes:

• Birth date
• Hire date
• Home address
• Office phone number
• Gender
• Resume

Lastly, you normalize the data.