weak entity

In a relational database, a weak entity is an entity that cannot be uniquely identified by its own attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key. The foreign key is typically a primary key of an entity it is related to.In entity relationship diagrams a weak entity set is indicated by a bold rectangle (the entity) connected by a bold type arrow to a bold diamond (the relationship). This type of relationship is called an identifying relationship and in IDEF1X notation it is represented by an oval entity rather than a square entity for base tables. An identifying relationship is one where the primary key is populated to the child weak entity as a primary key in that entity.
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