Cardinality (data modeling)

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In data modeling, the cardinality of one data table with respect to another data table is a critical aspect of database design. Relationships between data tables define cardinality when explaining how each table links to another. For example, in a database designed to keep track of hospital records there could be a table full of doctor information, and another table with patient information – with a many-to-one relationship between the records in the doctor table and records in the patient table. Tables can be related as any of: many-to-many, many-to-one, or one-to-one. This is said to be the cardinality of a given table in relation to another.

A crow's foot shows a one-to-many relationship, single line is a one-to-one relationship.