| 1. 9. 1. Understanding basic database terminology |
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A database consists of tables and columns. |
Database Design Terminology |
| Logical/Relational | Logical/Object-Oriented | Physical Implementation | | Entity | Class | Table | | Attribute | Attribute | Column | | Instance | Object | Row |
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Entity: An entity maps something in the real world. For example, departments within an organization, employees, or sales. |
Attribute: Represent information about an entity instance or an object. For example, the birth date or Social Security number of an employee. |
Entities (classes) are implemented in the database as tables. |
Attributes are implemented in the database as columns. |
Instances (objects) are implemented in the database as rows. |
A primary key uniquely identifies a specific instance of an entity. |
No two instances of an entity can have the same primary key. |
The values of all parts of the primary key must never be null. |
The most common types of primary keys in relational databases are ID numbers. |
Sometimes more than one attribute (or sets of attributes) can be used as a primary key. |