Chapter 5

Chapter 5

1. A database is is a base to store data in astructured manner

2. Table

   • Stores data about things that exist

3. Record

   • Each record stores data about an individual thing that exists

4. Entity

   • Another name for a record but with slightly different emphasis
   • Something that exists as a particular and discrete unit

5. Field

   • Columns within a table

6. Atribute

   • Another name for fields
   • Used when referring to the characteristics of entities

7. Primary key

   • A field that is a unique identification for each record

8. Composite key

   • Primary key that consits of 2 or more fields

9. Foreign key

   • A fieldin one table that links to a primary key in another table

10. Relationships

    • One to One
      • One record from one table relsates to only one record from another table
    • One to Many
      • One record from one table relates to Many records from another table
    • Foreign key always goes on the many side of the relationship
    • Many to Many
      • Many records in one table relate to Many records in another table
      • Not allowed
    • Referential Integrity
      • Ensures that data entered into the table on the many side exists on the one side

11. Duplicated data

    • Redundent can occur when relationships have not been set up correctly

12. Normalisation

    • Process of breaking down complex data structures into structured tables
    • Unnormalised Form (0NF)
      • Non-atomic data
      • Repeating groups of data
    • First normal form (1NF)
      • Must have a primary key
      • All data must be atomic
      • No repeating groups of data
      • Each field name must be unique
    • Second normal form (2NF)
      • Data is in 1NF
      • All non-primary key attributes must be dependent on the whole primary key
    • Third normal form (3NF)
      • Data must be in 2NF
      • All non-primary key attributes must be dependent on the primary key