If I have to model an online exam system, where I have 4 entities: Test Subject Question User Each Subject [has a number of] Questions Test [is based on a] Subject Test [contains] Questions Users [appears for] Test Based on above, I was wondering if Test composes Questions and Subject also composes Questions??? Should it be composition of Questions for both Subject and Test? In addition, Test is associated to Subject. But should Subject be an instance variable in Test? Isn't it composition then? regards Varun    More>>