Definicja cardinality

Co znaczy CARDINALITY:

A description specifying the number of dependent or target and independent or source entities in the relationship.

The two sides of the cardinality expression have the following significance:

n = 1, there is exactly one independent entity for each dependent entity. n = C, there may be entities of the dependent entity type that have no relationship to an entity of the source entity type. m = 1, there is exactly one dependent entity for each source entity type. m = C, there is at most one dependent entity for each source entity type. m = N, there is at least one dependent entity for each source entity type. m = CN, there is any number of dependent entities for each source entity type.