Hi Guys im trying to draw a erd with uml notation according to a case study, but im having difficulties as im a beginner.

Case study:

1) A department have many employees, although each department must have at least three employees. Every employee works for one and only one department. every department has a manager - only one manager per department. Clearly a manager is an employee of the company, but not all employees are managers.

2) A department may have many machines and every machine is assigned to a specific department.

3) A machine may be reported for maintenance numerous times. maintenance is done on a machine only once on a given day. some machines are so new they many not have required any maintenance yet.

here is what i've drawn so far:


As i think that Zero or more machines can be reported for maintenance and that Zero or more machines are maintained then there is a m:m relationship so we have to resolve it by adding a link entity. but im a bit confused on how to chose the Noun to describe the relation. and to solve it properly.

here is the actual case scenario, ive made some more mods to the design and added more entities:

A department may have many employees, although each department must have at least three employees. Every employee works for one and only one department. Every department has a manager – only one manager per department. Clearly a manager is an employee of the company, but not all employees are managers.

A department may have many machines and every machine is assigned to a specific department. A machine may be reported for maintenance numerous times. Maintenance is done on a machine only once on a given day. Some machines are so new they may not have required any maintenance yet.

Products are produced on machines. A product can be an assembly of several different components or a single piece. Every product/component goes through one or more machines for appropriate production processes. Likewise several products may go through a particular machine for some standard process.
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