Update anomalies
Learning outcomes for this page:
Be aware of certain 'update anomalies that occur
with tables which are not in second normal form
It is important to notice that if the surgical instruments table had not been converted to second normal form several problems would have occurred. The problems are associated with the various actions that can be carried out on records (create, update and delete) and are often referred to as update anomalies. Inspecting the surgical instruments tables the following problems would have arisen:
1. We cannot enter details about a supplier until that supplier supplies a part. If the supplier does not supply a part, there is no key ( a key field can not be null). This is known technically as a insert dependency problem.
2. If a supplier should temporarily cease to supply any part the deletion of the last record containing that supplier ID will also delete the details of the supplier. It would normally be desirable that supplier details be preserved. This is known technically as a delete dependency problem.
3. We have problems when we attempt to update the supplier details. We must search for every record which contains that supplier as part of the key. If a supplier supplies many parts, much effort is required. This is known technically as a update dependency problem.
When the table is split into second normal form the above problems disappear.
However even a table in second normal form can possess certain problems which are resolved if the table is converted to third normal form.Portfolio exercise: none m10|04|00
Time: 0 minutes
For: Clinicians | NHS managers | Non healthcare workers
Written by Robin Beaumont & Chris Noden e-mail:robin@ieg-net.co.uk or chrisnoden@hotmail.com
