![]() ![]() It may be of any data type, but the smaller ones are preferable. They serve as a reference for the particular row of data. The relationship between entities may exist only because of primary keys. It is an important concept within a relational database design. The primary key is a unique identifier of a row of an entity/table. An attribute is defined by these parameters: Except for standard documentation, the entity may provide its description. Bent Arrow symbol - represents a foreign key attributeĪn entity is specified by its attributes.Key symbol - represents a primary key attribute.Hash (#) - represents a foreign key attribute.Plus (+) - represents a primary key attribute.Other symbols may be used as a part of an attribute definition: Relationship - connects entities, it expresses how they are related to each other.Entity - represents a data type or a database table.This diagram type provides 2 basic kinds of elements:
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