Databases

Databases

1. Relationships

   • One to One
     • Common
   • One to Many
   • Many to Many
     • Break rules of normalisation

2. Normalisation

   • UNF
     • When a table is in un-normalised form.
   • 1NF
     • All data must be atomic
     • Each row must be uniquely identifiable.
     • Each field name must be unique
     • Each row needs a primary key
   • 2NF
     • All data needs to be dependent on the primary key.
     • 2NF is the removal of redundant data.
   • 3NF
     • No functional dependencies between non-key items.
     • All non-key items must be dependent on primary key.

3. Data Types

   • Boolean
     • Only stores two possible values.
     • Represents a question with only two possible answers
   • Integer
   • String

4. What is Data?

   • Un-processed information.
   • Should not be able to be understood.
   • Raw facts
   • Can be alphanumerical.

5. What is information?

   • Processed data
   • Can be understood.
   • Information = Data + [Structure]+[Context]+Meaning

6. What is a Data Dictionary?

   • Contains Metadata
     • Data about Data
   • Different packages will contain different things.

7. Advantages of Normalisation

   • No redundant data
   • Easier to maintain than un-normalised data
   • The stored data is atomic and can be combined in any structure.

8. Disadvantages of Normalisation

   • Requires higher use of CPU, memory and input and output devices as it requires more data.
   • Un-normalised databases are better for REPORTING
   • Normalised is better for TRANSACTIONAL.
   • Normalisation does not work with historical data.