Entity-Relationship Diagram for a library management system modeling four core entities: AUTOR, LIVRO, USUARIO, and EMPRESTIMO. AUTOR records author metadata including name, nationality, and birth date; LIVRO links to AUTOR via foreign key and tracks ISBN, genre, publication year, and inventory; USUARIO stores patron information; EMPRESTIMO connects LIVRO and USUARIO to log loan transactions with scheduled and actual return dates. This normalized schema eliminates data redundancy, enforces referential integrity, and supports queries for book availability, patron history, and overdue tracking. Fork and customize this diagram on Diagrams.so to adapt it for your library system, add additional entities like CATEGORIA or MULTA, or export as .drawio for use in database design tools.