Page 41 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database

Notes
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Case Study Requirements Analysis

T he owner of B&N has thought about what he wants and offers a concise summary:

“I would like my customers to be able to browse my catalog of books and to place orders
over the Internet. Currently, I take orders over the phone. I have mostly corporate
customers who call me and give me the ISBN number of a book and a quantity. I then
prepare a shipment that contains the books they have ordered. If I don’t have enough
copies in stock, I order additional copies and delay the shipment until the new copies
arrive; I want to ship a customer’s entire order together. My catalog includes all the books
that I sell. For each book, the catalog contains its ISBN number, title, author, purchase
price, sales price, and the year the book was published. Most of my customers are regulars,
and I have records with their name, address, and credit card number. New customers have
to call me first and establish an account before they can use my Web site.
On my new Web site, customers should first identify themselves by their unique customer
identification number. Then they should be able to browse my catalog and to place orders
online.”

DBDudes’s consultants are a little surprised by how quickly the requirements phase was
completed it usually takes them weeks of discussions (and many lunches and dinners) to
get this done but return to their offices to analyze this information.

2.3 Summary

 The relation, which is a two-dimensional table, is the primary unit of storage in a relational
database.
 A relational database can contain one or more of these tables, with each table consisting of
a unique set of rows and columns.

 A single record is stored in a table as a row, also known as a tuple, while attributes of the
data are defined in columns, or fields, in the table.
 The characteristics of the data, or the column, relates one record to another.

 Each column has a unique name and the content within it must be of the same type.
2.4 Keywords

Cross Product (*): This operator returns all the tuples of relation A plus all the tuples of
relation B.

Equi-Joins: Equi-join is same as conditional join, the only difference being only equity ‘=’
operator is used to join the two relations.
Joins: Joins are used to combine the information of two relations which have at least one field in
common.
Outer Joins: This is a special case “join” operator which considers the NULL values. Generally a
‘join’ operation performs the cross product of two tables and applies certain join conditions.

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