1. Case L University Hendro

2. Case Each postgraduate student at L University needs to maintain a list of references that he or she needs for research. For this purpose, references used are categorized into four types: book, article in a journal, conference paper, and PhD thesis. A reference can be included in one type only. The fields of each type of reference are listed in the following table.

3. Assuming that there are five classes, that is, References, Book, Article_Journal, Conference_Paper, and PhD_Thesis, develop the class hierarchy for the above description, and draw the corresponding class diagram. You also need to identify the relationship between references and another class, Postgraduate. Assume some attributes where necessary.

4. Solution There is an inheritance relationship between the reference object to the subclass type. The association between Postgraduate and References is many to many, where each reference can be used by many postgraduates, and each postgraduate can refer to many references.