A management system entity contact diagram

A house rental company plans to develop a management system to manage the information of its houses, tenants and employees.

The company has several apartment buildings, each apartment building has a unique building number and address, each apartment building has multiple apartments, and each apartment building has a unique number in the building (the apartment number of different apartment buildings can be the same). Employees and tenants have unique numbers in the system. For each tenant, the system records the name and contact number. Each apartment building must be managed by a manager. A tenant must sign a lease contract with the company. A lease contract is usually signed by one or more tenants (co-tenants) with the manager of the apartment building, and a tenant can rent multiple apartments.

This is the entity contact map: