EntityRelationship

The entity-relationship model is a conceptual data modeling approach used in database design to describe the structure of information. It represents data as entities, attributes, and relationships. Introduced by Peter Chen in 1976, the model treats an entity as a real-world object with distinct existence, an attribute as a property, and a relationship as an association between entities. Each entity type has a key that uniquely identifies its instances.

ER diagrams, or ERDs, visually encode the model. In Chen notation, entities are rectangles, relationships are diamonds, and attributes are ovals connected to their entities. Keys are underlined. Cardinality specifies how many instances participate in a relationship (one-to-one, one-to-many, many-to-many), while participation constraints indicate whether every instance participates (total) or only some (partial). Weak entities depend on a strong entity and are connected through identifying relationships.

Mapping to a relational schema: entity types become tables, attributes become columns, and relationships are implemented with foreign keys or separate junction tables for many-to-many cases. Weak entities produce dependent tables using the parent’s key as part of their primary key. Derived attributes can be computed from other attributes and are often omitted from the schema.

Use and scope: The ER model is widely used for conceptual and logical database design and serves as a common ground for analysts and stakeholders. Variants include Crow’s Foot notation and UML class diagrams. The model emphasizes structure over behavior and is typically complemented by other modeling approaches in complex systems.