Normalisation

Normalisation

1. a) Primary Key

   • In 1NF and 2NF
     • 1NF- Single Value in every cell
     • 2NF- No partial dependencies on primary keys
     • 3NF- A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key.

2. b) Update Anomalies

   • Insertion
     • certain attributes cannot be inserted into the database without the presence of other attribute
       • Eg : can't add a new course unless one student enrolled
   • Deletion
     • A Delete Anomaly exists when certain attributes are lost because of the deletion of other attributes
       • Eg Course info lost deleting last student.
   • Modification
     • when one or more instances of duplicated data is updated/ modified, but not all
       • Eg: Change address everywhere

3. c

   • describe by examples that the anomalies in part (b) are no longer true
   • show each table with only column headings 1 mark each for each key

4. 2 main ways-

   • examines the relationships between attributes in order to group them into tables that represent entities and relationships.
   • normalization could be used to validate the structure of tables derived from an ER model
   • Bottom-up approach to DB design
   • If relations not in 3NF = error when relations mapped from the ER model or that the ER model has an error

Bilder und Dateien der Mindmap