IT 221 (Part 4)

• Entity-relationship data model: high-level, conceptual, semantic data model
• Entity-relationship (ER) data model: introduced by Peter Chen
• Entity-relationship (ER) data model: introduced in March 1976
• Entity-relationship data model: based on a perception of a real world that consists of a set of basic objects called entities, and of relationships among these objects
• Entity-relationship (ER) data model database schema: Entity-Relationship Diagram
• ERD stands for Entity-Relationship Diagram.
• Entity Type: set of entities or entity instances
• Relationship Type: set of associations between/among entities
• Structural Constraints: represent two vital characteristics of a relationship type
• entity: a distinguishable “thing” or object in the real world
• entity: has attributes
• attributes: properties / characteristics stored in the database
• entity type / set: set of entities that share the same attributes
• entity type / set: each member entity is also referred to as an entity instance
• entity type / set: each instance is uniquely identified through a key attribute
• relationship: an “association” between (or among) entities
• relationship: may also have attributes
• relationship type / set: set of associations among the participating entity types
• relationship type / set: each association is referred to as a relationship or relationship instance