1. Library Management System -- Relational Data Model
Group 5
Paul Li
Babu Nepali
April 30, 2008

5. Subclassing library items
The catalog must support multiple item types (books, CDs, etc.)‏
This is a superclass/subclass relationship.
There are multiple ways to implement this.

6. Subclassing library items
An ITEM table holds attributes common to all library items
A separate BOOK table holds attributes that are specific to books.
Every book is represented by both an ITEM record and a BOOK record. They have the same primary key value.
An “ItemType” column in ITEM allows quick determination of the item type.

7. Subclassing (cont.)‏ ItemID INT (PK)‏ ItemID INT (PK, FK)‏
BOOK
ItemID INT (PK)‏
ItemType = 1
Title VARCHAR(255)‏
PublisherID INT
...
ItemID INT (PK, FK)‏
ISBN VARCHAR(13)‏

8. Subclassing (cont.)‏ ItemID INT (PK)‏ ItemType = 2
Similarly for “audio-visual” items:
ITEM
AUDIO_VISUAL
ItemID INT (PK)‏
ItemType = 2
Title VARCHAR(255)‏
PublisherID INT
...
ItemID INT (PK, FK)‏
Length VARCHAR(45)‏

9. Late fees A fine is charged for each day an item is overdue.
The total fine for an item cannot exceed a maximum amount.
Both the rate and amount are determined by the item type.

10. Late fees (cont.)‏ ... ... DateDue FinePerDay DateReturned MaximumFine
ITEM_LOAN
ITEM_LOAN
...
DateDue
DateReturned
FinePaymentDate
...
FinePerDay
MaximumFine

11. Late fees (cont.)‏ Fine for a single overdue item:
MAX( MaximumFine, (DateReturned – DateDue)‏
x FinePerDay )‏
A librarian records a payment by setting FinePaymentDate to the current date.

12. Late fees -- limitations
Patrons cannot pay an arbitrary amount.
An overdue item must be returned before the fine may be paid. (why?)‏
To increase the fine amount per date, the data model must be expanded. (why?)‏

13. Password hashes
Password hashes are stored in the PATRON and LIBRARY tables instead of the actual passwords.
“my_password” --> 041e0f26ab2429fb
When a user enters his password, the application recomputes the hash and compares it with the user's record.

14. Password hashes (cont.)‏
If someone steals my laptop, he would still not be able to log on to the system.