Draw a class diagram for the following situation (state any assumptions you believe you have to make in order to develop a complete diagram):

A consulting firm is organized as a partnership with five different types of employees: senior partners, junior partners, senior associates, associates, and assistants. Each employee has an annual salary; partners and associates also have a billing rate specified for them.

The firm needs to also know the amount of money each of the partners (both junior and senior) has invested in it. It is important for the firm to keep track of the history of salaries and billing rates. The firm works with a large number of clients; at any point in time, the firm may have several simultaneous engagements with any of the clients (or none). For each engagement, there is a billing factor that depends on the nature of the engagement; for final billing purposes, each employee’s billing rate is multiplied by the factor to determine the actual hourly rate charged for each employee’s work.

Employees are required to specify (with an application running on their smart phones) every transition from one engagement to another so that billable hours can be recorded with the highest level of accuracy possible.

In addition to the hours, the clients are charged for project-related expenses, which can be categorized as travel, lodging, supplies, information, and others. The firm sends a biweekly invoice to each of its customers.
The system has to maintain a record of when a specific item (labor cost or an expense item) was billed.
Obviously, it is essential to keep track of the payments that the clients send to the firm.