Relational Database Concepts

What is a Database?

• Database – A collection of permanently stored data that is:

               ---> Logically related (data relates to other data)

               ---> Shared  (many users may access data)

               ---> Protected  (access to data is controlled)

               ---> Managed  (data has integrity and value)

 

Relational Databases:

• A Relational Database consists of a set of logically related tables.
• A table is a two dimensional representation of data consisting of rows and columns.

Primary Key:

Primary Key values uniquely identify each row in a table.

In a relational model,

• A Primary Key is required for every table.
• Only one Primary Key is allowed in a table.
• It may consist of one or more columns.
• Primary Keys cannot have duplicate values.
• Primary Keys cannot be NULL.
• Primary Keys are considered “non-changing” values.

Foreign Key:

Foreign Key (FK) values identify table relationships.

• FK’s are optional  -  not all tables have them
• More than one FK is allowed per table
• FK’s can be made up of more than one column
• Duplicate values are allowed
• Missing (NULL) values are allowed
• Changes are allowed
• Each FK value must exist somewhere as a PK value

Advantages of a Relational Database Approach:

The advantages of a Relational Database compared to other database methodologies are many.

Relational database methodology:

• Is easy to use
• Is easy to understand
• Models the business, not the processes
• Is data-driven versus application driven
• Makes applications easier to build
• Supports trend toward end-user computing
• Is the industry standard for most large enterprises
• Allows businesses to respond to changing conditions more flexibly than other types