Databases

• Data - facts and figures - it is raw information
  • We create tables - primitive forms are spreadsheets

RDBMS

• To create data redundancy, and reduce data anomalies
• An ID is the first step to achieving data reliability

Normalisation

• Data Normalisation is the splitting of one table into multiple tables to separate key dependencies
  • This is so that in an Appointments table, for example, we can use a foreign key DoctorID instead of storing all of the doctor's details
• $1^{st}NF$
  • Primary Key - unique and not null or empty
  • If it does not have a 1stNF it is non-normalised data
• $2^{nd}NF$
  • You split data into multiple tables based on key dependencies
  • For example, in an items table, there can be a field for supplier and department
    • Yet, Item, Department and Supplier are all separate entities
• $3^{rd}NF$
  • You solve type of relationships between tables
    • any many to many between the tables

Cardinalities

• To set up a relationship between tables, we need a Primary Key and Foreign Key
• $1:1$
  • Between entities, for example wife and husband
• $1:N$
• $N:N$

ERD/DFD entities

• you will get backstabbed ? if you are a chef you will get shot ?