1. Lecture 8 Object Concepts
COP 4331 – OOD&P
Lecture 8
Object Concepts

2. UML – Intro. Case Study Problem:
Develop a computer system for a university library. The library currently uses a 1960’s program, written in an obsolete language for some simple bookkeeping tasks and a card index for user browsing. You are to build an interactive system which handles both of these aspects online

3. Case Study: Clarifying Requirements
Books and Journals
May have several copies of a book
Some books for short-term loan only
Other books 3 week loan
Only staff can borrow journals
Members can borrow up to 6 books
Staff can borrow up to 12 items
Items can be added or removed
Journals are bound at end of year

4. Case Study: Clarifying Requirements.2
Borrowing
Must keep track of when items are borrowed, due, and returned
Reminders for overdue items
In future borrowers my extend load in book is not reserved
Browsing
Anyone can search for book by title, author, etc
Check if book is available
Reserve book

5. Case Study: Use Case Model
Identify the tasks performed by each user of the system
User is called an actor in UML
Actor can also be an external system
Task is called a use case
Must analyze each use case in detail

6. Case Study: Use case Borrow copy of book
A BookBorrower presents a book. The system checks that the potential borrower is a member of the library and that s/he does not already have the maximum permitted number of items on loan. (6 for member, 12 for staff) If the check succeeds, the system records that the member has this copy of the book on loan. Otherwise it refuses the loan.

7. Use Case Diagram, fig 3.1

8. Case Study: Initial Simplification

9. Case Study: Identifying Classes
Consider nouns and noun phrases in problem description
Things in system include candidate classe

10. Candidate Classes
Books and Journals: The library contains books and journals. There may be several copies of a book. Some books for short-term loan only. All other books are for 3 week loan. Only a member of the staff can borrow journals. Library members can borrow up to 6 books at a time. Staff can borrow up to 12 items.

11. Candidate Classes.2
Borrowing: The system must keep track of when books and journals are borrowed and returned, enforcing the rules described above.

12. Candidate Classes.3 Filter list, remove bad classes
Library: out of scope of our system
Short-term loan: loan is really an event
Week: measure of time
Item: vague
Time: outside scope of system
System: from metalanguage of description
Rule: from metalanguage

13. Candidate Classes.4 This leaves Book Journal Copy (of book)
Library member
Member of staff

14. Candidate Classes.5
Library member and Staff member are users of the system
Users do not always occur inside the system
Unless their identity or other data about them needs to be retained

15. Relations Between Classes
Identify and name associations between classes
Names indicate relationship or interaction
Reveals multiplicity
Helps clarify understanding of system
Provides visualization of coupling

16. Initial Class Diagram, fig. 3.4

17. Revised Class Diagram, fig. 3.5

18. Interaction Daigrams
Show interactions between actors and objects in the system over time
Usually based on a use case or portion of one

19. Interaction Diagram, fig. 3.6

20. Changes in State: State Diagram, fig 3.7