ERdiagramme

ERDiagramme, often called ER diagrams, are schematic representations used in database design to illustrate data entities, their attributes, and the relationships between entities. They provide a high-level, conceptual view of a data model independent of a specific database system.

Core elements include entities (data objects such as Customer or Order), attributes (properties like customer_id or order_date), and relationships (associations such as "places" between Customer and Order). Entities have keys that uniquely identify instances; attributes may be simple, composite, multi-valued, or derived.

Notations vary. In Chen notation, entities are rectangles, attributes are ovals, and relationships are diamonds; Crow's Foot uses lines with symbols to express cardinality. Cardinalities express one-to-one, one-to-many, and many-to-many, while optionality indicates whether participation is mandatory.

Modeling process: begin with a conceptual model of requirements, refine to reduce redundancy, and map the diagram to a relational schema. The mapping translates entities to tables, attributes to columns, and relationships to foreign keys or join tables, with keys and constraints preserving integrity.

ER diagrams are widely used in database design and systems analysis to support planning, communication, and documentation. They are supported by many tools, enabling diagram creation, validation, and, in some cases, automatic schema generation. Limitations include scaling complex constraints and evolving requirements.