CS145 Assignment #1

Due Tuesday, October 9, 2001, 9:30AM

Some Mechanics for Homeworks

For All Students

Assignments are due in class on Tuesday. You are allowed one lateness of up to 48 hours; use that privilege carefully. Remember, you must hand in your assignment by the beginning of class; assignments handed in at the end of class will be considered late.

For On-Campus Students

Assignments should be turned in during class or at the course secretary's office: Gates Building room 419. If you want a receipt for your work, Ms. Weden can give you one.

For SITN students

Assignments due on Tuesday must be timestamped by the Wednesday-morning courier to be considered on-time. Like all students, you have one free 48-hour exception. You should not have to worry about receipts for work, because SITN logs everything it receives.

Remember: the due time/day of 9:30AM Tuesday applies to you too, although we often cannot verify the exact time you delivered your work to your local pickup point. However, please do not imagine, say, that it is OK to hand-deliver the work Wednesday morning.

Special Directions for Assignment 1 Only

In general, we shall expect your work to be handed in as one set of pages, fastened together, possibly with some electonic submission as well. However, because we want to look at your proposed projects quickly, we ask that, for this assignment only, you hand in three separate sets of pages, each with your name at the front. These three sections can be clipped together if you wish. They are:

The signed statement about rules for sharing ideas in CS145.
Step 1 of your Personal Database Application.
The three written problems at the end of this assignment.

Certification Regarding Honor-Code Policy

I feel bad that I have to take this step, but I have noticed an increasing number of students who, when confronted in an apparent case of plagiarism, tell me that they had never read the course policy on the subject. Therefore, I request that everyone download or paste the statement from The Course Introduction reproduced below, and sign it.

The basic presumption is that the work you do is your own. Occasionally, especially when working problem sets or writing programs (but never on exams!), it may be necessary to ask someone for help. You are permitted to do so, provided you meet the following two conditions.

You acknowledge the help on the work you hand in.

You understand the work that you hand in, so that you could explain the reasoning behind the parts of the work done for you by another.

Any other assistance by another person constitutes a violation of the honor code and will be treated as such.

If you have any questions about what this policy means, please discuss the matter with the instructor now.

Step 1 of Your PDA (Personal Database Application)

As the course progresses you will be building a substantial database application for a real-world scenario of your choosing. You will design a relational schema for the database, and you will create an actual database using a relational database management system. You will populate the database with sample data, write interactive queries and modifications on the database, and develop user-friendly tools for manipulating the database.

Your first step is to identify the domain you would like to manage with your database, and to construct an entity-relationship diagram for the data. We suggest that you pick an application that you will enjoy working with, since you'll be stuck with it for the whole quarter! In previous years, students who built a database about something they were interested in--a hobby, material from another course, a research project, etc.--got the most out of this part of CS145.

Try to pick an application that is relatively substantial, but not too enormous. For example, when expressed in the entity-relationship model, you might want your design to have in the range of five or so entity sets, and a similar number of relationships. In the past, we have accepted as reasonable those designs where the total number of entity sets plus relationships was in the 8-14 range, but have questioned others. Be aware, however, that entity sets or relationships that should be represented by attributes instead (a matter we'll discuss in class) do not ``count.''

You should certainly include different kinds of relationships (e.g., many-one, many-many) and different kinds of data (strings, integers, etc.), but your application is not required to use advanced features, such as subclassing, multiway relationships, or weak entity sets, if they are not appropriate for your application.

(a): Describe the database application you propose to work with throughout the course. Your description should be brief and relatively informal. If there are any unique or particularly difficult aspects of your proposed application, please point them out. Your description will be graded only on suitability and conciseness.
(b): Specify an entity-relationship diagram for your proposed database. As always, don't forget to underline key attributes and include arrowheads and rounded arrows indicating the multiplicity of relationships. If there are weak entity sets, indicate them by double lines, as described in class.

Preliminary Review of Projects

In order to catch problems at an early stage, everyone is required to have their design reviewed by the instructor or one of the TA's. We shall be announcing additional office hours during the few days before the project is due, so that everyone will have a chance for an individual discussion with a member of the course staff.

Reminders

We shall try to catch major problems in your proposed designs within three days of your submitting it, so your Step 2 of the PDA will not be adversely affected. To make sure we can tell you of a problem with your design, please include your email address on this part of the assignment.

Also, don't forget to save a copy of your PDA for reference as you do Step 2 of the PDA.

If you are having trouble thinking of an application, or if you are unsure whether your proposed application is appropriate, please feel free to consult with one of the course staff.

Problem Set

In this exercise, you will design a database for used cars, as might be used by an on-line trading site. The database will store automobiles for sale. Each automobile has a VIN (vehicle identification number), a model (e.g., Camero), a make (e.g., Chevrolet), a year (e.g., 1996), a color (e.g., red), a mileage (e.g., 50,000 miles), and a body style (e.g., coupe). Each automobile has a seller, which may be either a dealer or an individual. For dealers, the database has a name, address, and phone number. For individuals, only a phone number and email address are recorded.
In addition, articles about cars are maintained. Each article is about one model, make, and year of automobile, and each article has an author. The same author may write several articles about one make and model for one year. The database should connect cars with the articles about the make, model, and year of that car, although it need not make a direct connection.
Give an E/R design for this database. Briefly explain your reasoning, including the intuitive meaning of any relationships and any entity sets you use. Do not forget to indicate keys, many-one relationships, and weak entity sets in the appropriate ways.
Begin with the following two entity sets:
- States has key attribute name, and other attributes that need not concern us.
- Cities is a weak entity set related by a many-one relationship In to States. A city has a name, which is unique within a state, but not unique among all states (e.g., there are 24 states with a city named Springfield, but no state has two ``Springfields'').
Add the following information, and draw the entire E/R diagram:
1. There are bus companies. Each company operates within a single state, and no two bus companies in a single state can have the same name (although two different companies in different states could have the same name). Bus companies have addresses and phone numbers, in addition to a name.
2. There are bus routes. Each route has a number and operates within a single city. Route numbers are unique within a bus company, but two companies can have routes with the same number in the same city.
It is not always possible to replace a three-way relationship by two (or even three) two-way (binary) relationships. Suppose there is a three-way relationship among entity sets A, B, and C. Suppose also that there is some relationship set S representing the ``current value'' of this relationship. If we replace this relationship by relationships A-B, A-C, and B-C, we form the relationship sets for these new relationships by ``projecting'' each triple (a,b,c) in S onto its A and B components for A-B, and similarly for the other two binary relationships. Thus, for instance, (a,b) beecomes a pair in the relationship set for A-B.
Give an example of two relationship sets S1 and S2 (for the three-way relationship) that are different, and yet their projections onto the three binary relationship sets are each the same. Note that this situation demonstrates that the three-way relationship contains more information than the three two-way relationships. If you cannot solve this problem, then for partial credit try showing the same result, but assume that we use only two of the three binary relationships, e.g., S1 and S2 have the same projections for A-B and B-C only.