Data Modelling

1. Data Modelling
 : a technique for organising and documenting a system's data
 - data must be organised in a way that is flexible and adaptable to unanticipated business requirements

2. Database Design
 - Approaches
  * Conventional files
  * Databases approach which includes Relational model, Object-oriented model, Hierarchical model, Network model and Non-relational model
 - Methodology: For data design, the relational model and the OO model are the two which dominate contemporary software engineering.

3. Entity Relationship Diagram (ERD)
 : Graphical representation for Date Modelling
 - Entity: all systems contain data and data describes 'things'
 - Attributes: the pieces of data that we want to store about each instance of a given entity
  * one or more attributes must be defined as identifier - "key" to find an instance of the entity
  * Candidate key: a candidate to become the primary identifier of instances of an entity
  * Primary key: a candidate key which will most commonly be used to uniquely identify a single entity instance
  * Alternative key: any candidate key that is not selected to become the primary key
 - Relationships: associations between instances
  * Cardinality: One-to-One / One-to-Many / Many-to-Many
  * Modality: optional / mandatory

http://searchcrm.techtarget.com/definition/entity-relationship-diagram