SOLUTION

• The Business logic layer provides a high-level view of data and actions on data.
• The business logic layer contains objects that execute the business functions.
• The Command pattern should be considered to implement these objects.
• With the Command pattern, each use case in the requirements document is implemented as a separate command or set of commands executed in the business logic layer.
• The business-logic layer of an application for managing a university may provide abstractions of entities such as students, instructors, courses, sections, etc., and actions such as admitting a student to the university, enrolling a student in a course, and so on.
• The code implementing these actions ensures that business rules are satisfied; for example the code would ensure that a student can enroll for a course only if she has already completed course prerequisites, and has paid her tuition fees.