Relational Databases

Relational Databases

1. Based on tables

   • Tables are linked: Primary keys to Foreign keys
   • Each table is based on a real life entity
     • An entity is anything about which we store data
       • An entity has attributes, these are the characteristics of the entity, for example, customer_name, student_id, subject_level
   • A table consists of tuples (equivalent to records)
     • A tuple is information about one instance of an entity
       • For example, all we need to know about a customer called Fred

2. Use fixed length fields

3. Each column contains data of one type

4. There is no rule about the order of rows in a table

   • When order is required, indexes are added

5. No rule about the order of columns

6. No two rows can be identical

7. One column or combination of columns must be able to make each row unique