Draw an er diagram for each of the following situations. on the diagram be sure to identify the cardinality, existence, and optionality (for subtypes) of each relationship.
1. a company has a number of employees. each employee may be assigned to one or more projects, or may not be assigned to a project. a project must have at least one employee assigned, and may have several employees assigned.
2. a university has a large number of courses in its catalog. each course may have one or more other courses as prerequisistes, or may have no prerequisites.
3. a college course may have one or more scheduled sections, or may not have a scheduled section.
4. a hospital patient has a patient history. each patient has one or more history records (we assume that the initial patient visit is always recorded as an instance of the history). each patient history record belongs to exactly one patient.
5. a video store may stock more than one copy of a given movie. it is also true that the store may not have a single copy of a paticular movie.