soghra1990
عضو جدید
سلام
من منظور این سوال رو نمی فهمم
Exercise 2.2 A university database contains information about professors (identified
by social security number, or SSN) and courses (identified by courseid). Professors
teach courses; each of the following situations concerns the Teaches relationship set. For
each situation, draw an ER diagram that describes it (assuming no further constraints
hold).
1. Professors can teach the same course in several semesters, and each offering must
be recorded.
2. Professors can teach the same course in several semesters, and only the most
recent such offering needs to be recorded. (Assume this condition applies in all
subsequent questions.)
3. Every professor must teach some course.
4. Every professor teaches exactly one course (no more, no less).
5. Every professor teaches exactly one course (no more, no less), and every course
must be taught by some professor.
من منظور این سوال رو نمی فهمم
Exercise 2.2 A university database contains information about professors (identified
by social security number, or SSN) and courses (identified by courseid). Professors
teach courses; each of the following situations concerns the Teaches relationship set. For
each situation, draw an ER diagram that describes it (assuming no further constraints
hold).
1. Professors can teach the same course in several semesters, and each offering must
be recorded.
2. Professors can teach the same course in several semesters, and only the most
recent such offering needs to be recorded. (Assume this condition applies in all
subsequent questions.)
3. Every professor must teach some course.
4. Every professor teaches exactly one course (no more, no less).
5. Every professor teaches exactly one course (no more, no less), and every course
must be taught by some professor.