Database Design & Development

Database Design & Development

1. Entity Relationship Diagrams

2. Definitions

   • Entity
     • Entity - An entity is a person, place, thing, event or concept of interest to the business or organisation about which data is to be stored, AKA a table
   • Attribute
     • Attribute - An entity is described by its attributes. Each attribute is a characteristic of the entity, AKA, a field. For example, attributes of the Student entity would include studentID, firstname, surname and dateOfBirth
   • Primary Key
     • Primary Key - An attribute that uniquely identifies one, and only one, entity occurrence is called a primary key. For example, the primary key of the Student entity would be studentID.  A primary key is shown by underlining in the entity-relationship diagram.
   • Foreign Key
     • Foreign Key - An attribute in one table that uniquely identifies a row of another table, i.e. a primary key.  They are used to connect two entities together.A foreign key is signified by an asterisk in the entity-relationship diagram.
   • Compound Key
     • Compound Key - A compound key is a primary key that is made up of two or more attributes.

3. Relationships

   • A relationship is a natural association between one or more entities.
   • For example, Students learn Subjects and Teachers educate Students.

4. Cardinality

   • The cardinality of a relationship defines the number of participants in the relationship.