Apêndice A. Diagrama ER para a base de dados de exemplo
A Figura A-1 é um diagrama entidade-relacionamento (ER) para a base de dados de exemplo utilizada neste livro. Como o nome sugere, o diagrama mostra as entidades, ou tabelas, no banco de dados, juntamente com os relacionamentos de chave estrangeira entre as tabelas. Aqui estão algumas dicas para te ajudar a compreender a notação:
Cada retângulo representa uma tabela, com o nome da tabela acima do canto superior esquerdo do retângulo. A(s) coluna(s) de chave primária é(são) listada(s) primeiro, seguida(s) pelas colunas não-chave.
As linhas entre as tabelas representam relações de chave estrangeira. As marcações em cada extremidade das linhas representam a quantidade permitida, que pode ser zero (0), um (1) ou muitos (<). Por exemplo, se observares a relação entre as tabelas customer e rental, dirás que um aluguer está associado exatamente a um cliente, mas um cliente pode ter zero, um ou muitos alugueres.
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