CIS-552 Database Design
Fall 2009

Homework #1
Due: Monday October 5

Introduction

In this assignment you will implement a class called SlottedPage for managing pages of variable length records. The SlottedPage class is part of the java cis552 package for a rudimentary DBMS buffer and file manager. You should read the documentation for the cis552 package, paying special attention to the SlottedPage class. A zip file with the cis552 library (minus the SlottedPage class) and other materials can be downloaded here. We will discuss the design of the cis552 package and the slotted page structure in class.

Assignment

Write an implementation of a subclass of Page called SlottedPage. Its interface should be exactly the same as the interface as described in the documentation. Read the documentation carefully to understand how each method should behave. There are several additional requirements beyond what is stated in the API documentation:

The data portion of the page should be maintained in compacted form. That is, there should never be any unused space between records. When a record is deleted, the remaining records should be rearanged on the page to fill in the gap, and the slot directory should be updated accordingly. However, once a record has been inserted in the page its rid (record id) must not change, which means its directory entry cannot be moved.

The page size is defined as a constant in the Page class, PAGE_SIZE. You should use this constant in your code, so that no modifications are needed when the page size changes.

In principle, you could put the slot directory at either end of the page, with data growing from the opposite end. Also, you could in principle use your own scheme for record id's. However, to be compatible with the db files you are given, you must use exactly the same page format as we discussed in class. You should make sure you are able to read records from the people.db file you are given.

Write a main method to thoroughly test your SlottedPage class. You will not be graded on your main method, but I will be running my own tests, and I'm good at finding errors! You should expect to write at least as much code to test your class as you do to implement it!!

Tips

You are given a file, people.db, which uses the slotted page format. You may use this file to help test your implementation. The people relation is part of a database for an automobile insurance company. The database schema is here. For simplicity, each record is a String that has been converted to a byte array. The fields within each record are separated by tabs. There is also a plain text file, people.txt, with the same data in human readable form: one record per line of tab delimited fields.

The String class has a constructor that takes a byte array as argument, String(byte[] bytes), and a method that encodes the string as a byte array: byte[] getBytes().

In order to manipulate the slot directory, it is recommended (but not required) that you write a couple of utility methods for reading and writing 16-bit shorts from some offset within a byte array. Make sure you handle the value -1 correctly!

There is no reason to extract class files from the cis552.jar file. Just make sure the jar file is in your compiler's classpath.

Your SlottedPage class needs to be defined in the cis552 package. The first non-blank, non-comment line in your SlottedPage.java file should be: package cis552;

What to turn in

Send a soft copy of your source code file, SlottedPage.java as an email attachment to pbergstein@umassd.edu.

CIS-552 Database DesignFall 2009