I'm new here and i wonder if this is the right place to ask this question.
Basically i'm in the process of developing a library system demo and plan to use hibernate for my DB layer. what i have planned to do is to convert my object model into relational. The main issue that i have concerns inheritance.


I have so far identified 2 inheritance hierarchies involving the users of the library system and the library items. I have  a normal LibraryUser(student), MemberOfStaff(lecturer/prof) and Librarian who all inherit from LibraryMember. I also have Book, Journal, CD-ROM and Tape who all inherit from LibraryItem.


One of the main problem is should i map all the inheritance hierarchies to a single table or each concrete class to a table or each class to a table? In case of hibernate i think that is a case of using either sub-class or joined-sub-class or just class.


At the code level(domain object) my confusion lies here:

[b]either[/b]
public class user 
{
 .....
  Set borrowedBooks;
  Set borrowedCDs;
  ....
  settters/getters
  .......
}

in the above case i think i'll be using separate tables and it'll be easier to add items like books,journals..


[b]OR[/b]

[code]
public class user 
{
 .....
  Set borrowedLibraryItems;
   ....
  settters/getters
  .......
}

[/code]
In this case i'm representing borrowed items using the superclass. With this scenario how would i insert/retrieve a specific item(as a libraty item might be a book journal/book/cd ?). 


the other thing in this dilemma is that any one(staff and librarian) except the student can borrow a journal.


So my main questions/confusion, should i map to a single table for hierarchies or several tables and should i maitain references using the sperclass or subclasses?