Peter Pin-Shan Chen proposed the entity-relationship model in his 1976 paper. It represents the application world through entities, relationships and attributes, together with a diagrammatic method for database design. The model aims to preserve semantic distinctions before translating them into a particular database representation.[ref]
For example, a relationship between an employee and a project can carry an hours-worked attribute. That quantity belongs to the participation relationship, not to the employee or project alone. Making its placement explicit helps avoid duplicating or misinterpreting facts when designing a relational schema.
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