This page is about relationship in a relational model.
In a relational model, as a relation (generally a table) can model:
Therefore, a relationship between two relations is not always a relations between two entities.
cardinality define the type of relationships between two relations.
Because most of database only support one-to-many relationships, it is necessary to implement other relationships physically via a third junction table (association table).
Mapping: Information about the number of entities in each entity set which is allowed in a relationship set is indicated by specifying 1, m, % in the diagram
In a data model, two main relationship are used :
but you can found other types as :
To describe precisely the type of relationship in a data model, you use the cardinality.
The following tables are the most common tables that holds a relationship:
Every table with a foreign key holds a relationship.