Understand that the use of a relational database facilitates the…

The idea

A relational database stores data in separate linked tables so each fact is recorded once. Data redundancy means the same data is stored in more than one place; data inconsistency means copies of the same data disagree. If a student's address were copied into every results row, updating one copy and missing another would create inconsistency. By keeping the address once in a Student table and linking results via a foreign key, redundancy is removed and inconsistency cannot arise from duplicated copies. Normalisation, splitting data into related tables, is the process that achieves this. The benefit is accurate, easier-to-maintain data, though it requires correct linking through keys.

What earns the marks

• Defines data redundancy as storing the same data in more than one place.
• Defines data inconsistency as different copies of the same data disagreeing.
• Explains that storing each fact once in linked tables removes redundancy.
• Explains that removing duplicate copies prevents inconsistency when data is updated.
• Links the benefit to using keys and separate related tables (normalisation).

Common mistakes and how to put them right

• Treating redundancy and inconsistency as the same thing.

  Put it right: Redundancy is duplicated storage, while inconsistency is conflicting values arising from those duplicates.

• Assuming a relational database automatically removes all errors.

  Put it right: It reduces redundancy and inconsistency only when data is properly structured into linked tables.

• Thinking more duplication improves reliability.

  Put it right: Duplication increases the risk of inconsistency when only some copies are updated.

Exam tips

• Define both terms precisely before explaining how the relational model removes them.
• Use a worked example, such as an address stored once and referenced by a key, to show the benefit.
• Link your answer to keys and separate tables to show understanding of how the elimination happens.