ICT - Databases

ICT - Databases

1. RDMS

   • Relational Database Management System

2. Record

   • A single row within a table that contains data about a single item or event

3. Table

   • A collection of records

4. Field

   • Individual data item within a record

5. Keys

   • Primary
     • Is a unique reference within a table
   • Secondary
     • Is a field that can be used for indexing data
   • Foreign
     • Used to link tables

6. Relationships

   • ER diagrams - Entity relationships models
   • One to One
     • One person has one passport
   • One to Many
     • One employer has many employees
   • Many to Many
     • Many classes have many teachers

7. Referential integrity

   • Prevents you deleting related records

8. Flat file database

   • All of the data is stored in one large table

9. Why use?

   • It lets you store vasts amount of data
   • Queries can be run to search for records or groups of records
   • Reports can be produced

10. Entities

    • Each table is about an object, person or thing

11. Attributes

    • Each entity is made up of a number of attributes which represent that entity
    • Customer = Entity Customer ID, First name Surname, D.O.B, Address, Phone no = Attributes

12. Normalisation

    • Why?
      • Minimizes duplication of data
      • Safeguard against logical or structure problems
      • Helps organise
    • What?
      • 0NF
      • 1NF
        • There are no columns with repeated data (horizontally)
        • Each data item cannot be broken down any further (atomic data)
        • Each field name is unique
        • Each row has a primary key
      • 2NF
        • Must be in 1NF
        • Attributes must relate to each part of primary key
      • 3NF
        • Must be in 2NF
        • There are no non-key attributes that depend on another non-key attribute
    • Advantages
      • No redundant data
      • No duplication
    • Disadvantages
      • More tables
      • More difficult to complete relationships
      • Cross table queries