Entity Relationship (ER) Model
- model used to identify and represent entities and the relationships amongst them
- specifies the schema & represents overall logic
- er diagrams are used for visual representation
Entities
- possess unique instances
- have properties or attributes that “describe” or define them
- entity set refers to a collection of similar entities (eg: students in a class)
- types - strong & weak entities
- strong entities are ones with primary keys & no dependencies
- weak entities are dependent on strong entities
- composite entity combines multiple entities into single entity to represent a relationship between them
Attributes:
- simply refers to properties that are used to “describe” an entity
- translates to columns in a table