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

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.

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.

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)‏

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)‏

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.

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

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.

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?)‏

Password hashes Password hashes are stored in the PATRON and LIBRARY tables instead of the actual passwords. “my_password” --> 041e0f26ab2429fb9824123 When a user enters his password, the application recomputes the hash and compares it with the user's record.

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