Draw ERD with Chen Notation for the case study below.

The Metropolitan Housing Agency (MHA) is a non-profit organization that deals with the development and improvement of affordable housing. The MHA operates in a metropolitan area in a city. Its operations include management and maintenance of apartments and townhouses for people with low income.

The MHA maintains data about location, availability, and condition of housing in 11 different census tracts in the metropolitan area. Within the boundaries of each tract there are approximately 30 different buildings that provide low-income housing. Each building contains from 6 to 30 units (apartments or townhouses).

The MHA keeps data about each census tract including ID, geographical location (region in the city) and median income of the population. The agency receives money from sponsors. A sponsor can be a person or a company. A sponsor is described by ID, name, address, phone number. The same sponsor may donate to different census tracts and make several donations per year irregularly. A donation is described by unique ID, the date when it was made and amount. The donations are used to reduce the rent for qualified people in a given census tract.

For each building MHA records name, size (in units), address, availability of facilities for people with special needs. Each unit is assigned a unique number within its building and is characterized by the number of bedrooms, monthly rent. If it is occupied, information about associated tenant(s) is required. For apartments it is necessary to record their location in the building, for townhouses extra charges, availability of a backyard. Tenants are described by their names, phone numbers and yearly income.

All buildings are maintained by MHA employees. Each tract is managed by a MHA department. Each department is described by id, name and phone. Each department has a manager, own budget. Each building has a manager and a few workers, who report to the building manager. A building manager reports to a department manager. If repair service needs to be done, it must be approved by building manager. If renovation is required, it must be approved by department manager. Each employee is described by employee ID and name and can work in at most one department.