1. Copyright ©2014 Pearson Education, Inc. Chapter 3 Requirements and Business Rules Chapter3.1

2. Copyright ©2014 Pearson Education, Inc. Client Server Relations Much of software can be divided into one of two types: Servers Clients Chapter3.2

3. Copyright ©2014 Pearson Education, Inc. 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.) Chapter3.3

4. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.4

5. Copyright ©2014 Pearson Education, Inc. Client Server Example Chapter3.5

6. Copyright ©2014 Pearson Education, Inc. 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.” Chapter3.6

7. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.7

8. Copyright ©2014 Pearson Education, Inc. 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 Chapter3.8

9. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.9

10. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.10

11. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.11

12. Copyright ©2014 Pearson Education, Inc. 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? Chapter3.12

13. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.13

14. Copyright ©2014 Pearson Education, Inc. Types of Security Requirements Type of AccessDescription CreateThe permission to make new database objects such as tables or views AlterThe permission to modify database objects DropThe permission to remove database object SelectThe permission to see data in a table or view UpdateThe permission to modify data in a table InsertThe permission to add data rows to a table DeleteThe permission to remove data rows from a table ExecuteThe permission to run database executables such as stored procedures Chapter3.14

15. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.15

16. Copyright ©2014 Pearson Education, Inc. 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.” Chapter3.16

17. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.17

18. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.18

19. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.19

20. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.20

21. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.21

22. Copyright ©2014 Pearson Education, Inc. Attributes Attributes represent data that describe entities. Attributes of student, for instance, include: Student ID Student Name Student Address Student Phone, etc. Chapter3.22

23. Copyright ©2014 Pearson Education, Inc. 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 Chapter3.23

24. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.24

25. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.25

26. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.26

27. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.27

28. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.28

29. Copyright ©2014 Pearson Education, Inc. Comparison Between Natural and Surrogate Keys: Advantages Natural Keys Protect better against accidentally repeating the same information. Belong to the entity and tend to make foreign keys more understandable. Surrogate Keys 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. Chapter3.29

30. Copyright ©2014 Pearson Education, Inc. Comparison Between Natural and Surrogate Keys: Disadvantages Natural 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). Surrogate Key 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. Chapter3.30

31. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.31

32. Copyright ©2014 Pearson Education, Inc. 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. Chapter3.32