Design an ER schema for a database application described as following:

A project (identified by its unique Project-Number, a project name, and a start date) consists of several work packages (a work package is described by a unique WP-number, a description, a start date, and a due date).

Work packages are structured into a hierarchical work breakdown structure, whereby a work package can be subdivided into several further work packages, while each work package is subordinated to exactly one work package.

One or more employees are assigned to each work package, whereby employees can also be employed in several work packages. An Employee described by its unique ID, a name, an address a phone number and many qualifications. Employees are uniquely assigned to departments.

A department number and a name uniquely identify a department. It also has a location, a manager and a phone number.

Each project has an employee as a responsible person; however, an employee can also have responsibility for several projects.