Domain Model

Design decisions:

1. Created User class which has student, employer, coop administrator and academic manager generalizations. This makes the organization more clean.
   
2. Created the id attribute for each class. The id is used as the primary key attribute to differentiate each object.
   
3. Created two data structures, date and time to have a better representation of some data.
   
4. Create one enum data structure state which has two elements: inactive and active for coopTerm state attribute.
   
5. Add both bidirectional and unidirectional associations between classes.