You are developing a system for a project management company. The company's employees sign a contract when being hired. Each employee can have only one contract with the company, while more than one employee cannot have the same contract with the company. Employees have managers who manage their work. Each employee can only have one manager, but a manager can be in charge of several employees. Several employees can participate in the development of a same project. Moreover, an employee can participate in several projects.
Map relationship types to entities.