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Chapter 3
Requirements and Business Rules
Copyright ©2014 Pearson Education, Inc.
Chapter3.1
Client Server Relations
• Much of software can be divided into one of two types:
• Servers
• Clients
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Chapter3.2
Servers
• A server is software that offers “services” to other software.
• For instance, a web server provides web pages that are
requested by a browser.
• Databases usually behave as servers.
• (Some machines are optimized to host server software. They are
also commonly referred to as servers.)
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Chapter3.3
Clients
• Clients are software that request services.
• A browser, for instance, requests a web page to load and view.
• An application client can request data from a database.
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Chapter3.4
Client Server Example
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Chapter3.5
Review of the Issues
• Reviewing the issues with the current data management system
is a good place to start.
• Several of the requirements of the new database will be to
resolve those issues.
• Reviewing the issues also helps you refocus on the “problem
domain.”
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Chapter3.6
Problem Domain
• The problem domain represents the business problems a
database is meant to solve.
• For a retail sale database, for instance, the problem domain is
the sale and all that is involved with the sale.
• For a science database dealing with earthquakes, the domain
would be the locations, sizes, and depths of earthquakes.
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Chapter3.7
Requirements
• It is important to identify all the requirements of the database.
• A requirement represents something the database must store or
do.
• There are several types of requirements:
• Data requirements
• Report requirements
• Security requirements
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Chapter3.8
Data Requirements
• Data requirements refer to the attributes the database must
store in order to meet the information needs of an organization.
• It is important to identify these data requirements as completely
as possible.
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Chapter3.9
Report Requirements
• Report requirements refer to the reports the database will have
to generate.
• For example, the tutor database will have to report on tutor’s
hours, the numbers of unduplicated student sessions, and the
demographics of the students using the tutoring services, among
others.
• The data required to generate those reports must be in the
database.
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Chapter3.10
Security Requirements
• Security requirements refer to the limits that must be placed on
database access in order to protect the integrity and privacy of
the data in the database.
• Typically, different users of the database will have different levels
of access depending on their needs.
• A user should have access to the data and resources they need
to do their work, but no more.
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Chapter3.11
Stakeholders and Requirements
• It is useful to think about requirements in terms of each of the
stakeholders who will be using the database.
• What does that particular stakeholder need to do with the data
in order to do their job?
• What are the limits on what each stakeholder should be able to
do?
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Chapter3.12
Access Requirements
• Access is usually defined in terms of what kinds of things a user
can do in the database.
• For instance, a user can be given permission to SELECT some
data – that is, to view it – but not other data.
• They may be given permission to edit certain data, but not all
data.
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Chapter3.13
Types of Security Requirements
Type of Access
Description
Create
The permission to make new database objects such as tables or views
Alter
The permission to modify database objects
Drop
The permission to remove database object
Select
The permission to see data in a table or view
Update
The permission to modify data in a table
Insert
The permission to add data rows to a table
Delete
The permission to remove data rows from a table
Execute
The permission to run database executables such as stored procedures
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Chapter3.14
Business Rules
• A business rule is a rule about how data is collected, stored, or
processed.
• Examples of business rules:
• All quarter grades must be between 0 and 4.
• No patron can have more than 20 items checked out at a time.
• Payments must be made within 30 days or a 25-dollar late fee will be
added.
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Chapter3.15
Enforcing Business Rules
• Some business rules can be enforced in the database itself by
placing constraints on the data. (The quarter grade must be
between 0 and 4.)
• Other business rules must be enforced through other means,
such as “triggers.”
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Chapter3.16
Triggers
• A trigger is a block of SQL code that is triggered by an event such
as an INSERT, UPDATE, or DELETE.
• Triggers can be used to enforce things such as “No patron can
check out more that 20 items.”
• When the database inserts a new item, the trigger fires and
totals the number of unreturned items. If it is greater than 20, it
can notify the librarian or the patron.
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Chapter3.17
Reviewing Requirements and Business
Rules
• When you have listed out all the requirements and business rules
you can discover, you should always review them with the chief
stakeholders.
• Use the review to make sure you have a complete list of
requirements.
• Also, make sure you have understood the business rules and
processes.
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Chapter3.18
A Little Bit of Grammar
• This is a technique to help identify the data requirements for a
database.
• Review all the documents, interviews, and questionnaires, and
list all the major nouns.
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Chapter3.19
Grouping Around Themes
• The next step is to sort the nouns into broad themes or groups.
• These themes may become entities in your database design.
• The other nouns that belong to those themes will become
attributes.
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Chapter3.20
Entities
• Entities are things that the database is concerned with.
• In the tutoring database, for instance, major themes are student,
class, tutor, session, and request.
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Chapter3.21
Attributes
• Attributes represent data that describe entities.
• Attributes of student, for instance, include:
•
•
•
•
Student ID
Student Name
Student Address
Student Phone, etc.
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Chapter3.22
Keys
• When you have your preliminary entities and attributes defined,
you can start thinking about keys.
• There are several types of keys:
•
•
•
•
•
Primary Keys
Candidate Keys
Natural Keys
Composite Keys
Surrogate Keys
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Chapter3.23
Primary Keys
• A primary key uniquely identifies a row of data.
• A primary key must be unique for every row (that is, it can never
repeat in the table that will result from the entity).
• For instance, a student ID can uniquely identify an individual
student and the data associated with him or her.
• Every entity should have a primary key.
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Chapter3.24
Candidate Keys
• A candidate key is an attribute or attributes of an entity that
have the potential to become a primary key.
• Candidate keys are not actual keys, but are a list of attributes
that should be considered when choosing the primary key.
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Chapter3.25
Natural Keys
• There are basically two ways of making keys: natural and
surrogate.
• Natural keys are keys formed by using an attribute that
“naturally” belongs to the entity, such as a student ID or a phone
number.
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Chapter3.26
Composite Keys
• Composite keys are keys composed of more than one attribute.
• For example, to get a unique designation of a course section, it is
necessary to combine the quarter, the year, and the item
number.
• Composite keys are one key made out of many parts.
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Chapter3.27
Surrogate Keys
• Surrogate keys are keys that have no business meaning.
• Often they are just integers incremented row by row.
• They can also be things such as time stamps of auto-generated
GUIDs.
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Chapter3.28
Comparison Between Natural and Surrogate
Keys: Advantages
Natural Keys
Surrogate Keys
• Protect better against
accidentally repeating the
same information.
• Belong to the entity and tend
to make foreign keys more
understandable.
• Are always unique.
• Do not contain any business
logic and are therefore not
subject to changes in
business rules.
• Are easier to define and use.
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Chapter3.29
Comparison Between Natural and Surrogate
Keys: Disadvantages
Natural Key
Surrogate Key
• Hard to guarantee their
uniqueness.
• May require clumsy composite
keys consisting of several
attributes to be unique.
• Subject to changes in business
rules (think of Social Security
numbers, for instance).
• Automatically grant
uniqueness to a row, making
it easier to accidentally insert
the same information twice.
• No relation to the data,
making database relations
less readable.
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Chapter3.30
Documentation
• All requirements and business rules should be documented
clearly and stored.
• Even preliminary definitions of entities, attributes, and keys
should be kept for later reference.
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Chapter3.31
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any
form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written
permission of the publisher. Printed in the United States of America.
Copyright ©2014 Pearson Education, Inc.
Chapter3.32