Chapter 5_1

Chapter 5_1

1. 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
   • No redundent data
   • Integrity of data increased
   • Database is easier to maintain
   • More flexibility for future expansion
   • Reduced database performance
   • Coded data
   • Complex queries

2. Data dictionary

   • Names of each table within a database
   • Field names within a table
   • The primary key for each table which willbe unique for each record
   • Indexed fields within each table that will improve search times
   • Length of each field
   • Data types for each field
   • Default values for fields that are used when a new record is created
   • Validation to show that rules for data that is entered within fields and the error messages
   • Foreign keys that are used within each table
   • Relationships between the tables within a database including the degree of the relationship

3. Queries

   • Static
     • Criterion does not change each time the query is processed
   • Dynamic
     • Criterion can change each time the query is processed
   • Simple
     • Only has a single criterion
   • Complex
     • A query which has two or more criteria