would the police officers union have an opinion if the mayor of the city wanted to change the hiring and promotional policies of its police department? if so, what values would be identified?

also what kind of relationship exists between the mayor of the city and the chief of police? what types of roles and responsibilities do they each have?

what is a civil service system? or a civil service department?

i need help understanding these concepts for a class i am taking. if anyone can break it down for me that would be great! thanks!
lisa