Database

The data is stored in one or more separate computers files

Is a way of structuring information in tables, rows and columns.

• Data redundancy (data is repeated in more than one file)

• Data dependency (changes to data means changes to program accessing the data)

• Lack of data integrity (entries that should be same can be different in different places)

• Lack of data privacy (all users have access to all data if a single flat file)

• Reduce data redundancy

• Reduce data dependency

• Improve data integrity

• Improve data privacy

• Program-data independence

• Ability to create ad hoc queries (queries designed for a particular purpose)

1. Multiple tables are linked together

   • which reduces data redundancy

   • increase data integrity

   • referential integrity can be enforced

2. Program data independence means that

   • structure of data can change and does not affect program

   • structure of program can change and does not affect data

3. Complex queries can be more easily written

   • to find specific data

4. Different user can be given different access rights

   • which improves security

5. Different users can be given different views of the data

   • so they do not see confidential information and data privacy is maintained

The concept or object in the system that we want to model and store information about

A data item, represented as a field within a table

A unique identifier for each tuple

• primary key uniquely identifies each tuple

• primary key can be used as a foreign key in another table

• to form relation between the tables