Systems Analysis and Design 9th Edition

Chapter 9Data Design

Chapter Objectives

• Explain file-oriented systems and how they differ from database management systems

• Explain data design terminology, including entities, fields, common fields, records, files, tables, and key fields

• Describe data relationships, draw an entity relationship diagram, define cardinality, and use cardinality notation

• Explain the concept of normalization

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Chapter Objectives

• Explain the importance of codes and describe various coding schemes

• Explain data warehousing and data mining• Differentiate between logical and physical

storage and records• Explain data control measures

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Introduction

• Begins with a review of data design concepts and terminology, then discusses file-based systems and database systems, including Web-based databases

• Concludes with a discussion of data storage and access, including strategic tools such as data warehousing and data mining, physical design issues, logical and physical records, data storage formats, and data controls

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Data Design Concepts

• Data Structures– Each file or table

contains data about people, places, things or events that interact with the information system

– File-oriented system– Database management

system (DBMS)

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Data Design Concepts

• Overview of File Processing– File processing can be

efficient and cost-effective in certain situations

– Potential problems • Data redundancy• Data integrity• Rigid data structure

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Data Design Concepts

• Overview of File Processing– Various types of files• Master file• Table file• Transaction file• Work file• Security file• History file

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Data Design Concepts

• The Evolution from File Systems to Database Systems– A database management

system (DBMS) is a collection of tools, features, and interfaces that enables users to add, update, manage, access, and analyze the contents of a database

– The main advantage of a DBMS is that it offers timely, interactive, and flexible data access

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Data Design Concepts

• The Evolution from File Systems to Database Systems – Some Advantages• Scalability• Better support for client/server systems• Economy of scale• Flexible data sharing• Enterprise-wide application – database administrator

(DBA)• Stronger standards

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DBMS Components

• Interfaces for Users, Database Administrators, and Related Systems– Users

• Query language• Query by example (QBE)• SQL (structured query

language)

– Database Administrators• A DBA is responsible for

DBMS management and support

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DBMS Components

• Interfaces for Users, Database Administrators, and Related Systems– Related information systems• A DBMS can support several related information

systems that provide input to, and require specific data from, the DBMS• No human intervention is required for two-way

communication

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DBMS Components

• Data Manipulation Language– A data manipulation language (DML) controls

database operations, including storing, retrieving, updating, and deleting data

• Schema – The complete definition of a database, including

descriptions of all fields, tables, and relationships, is called a schema

– You also can define one or more subschemas

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DBMS Components

• Physical Data Repository– The data dictionary is transformed into a physical

data repository, which also contains the schema and subschemas

– The physical repository might be centralized, or distributed at several locations

– ODBC – open database connectivity– JDBC – Java database connectivity

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Web-Based Database Design

• Characteristics of Web-Based Design

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Web-Based Database Design

• Internet Terminology– Web browser– Web page– HTML (Hypertext Markup Language)– Tags– Web server– Web site

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Web-Based Database Design

• Internet Terminology– Intranet– Extranet– Protocols– Web-centric– Clients– Servers

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Web-Based Database Design

• Connecting a Database to the Web– Database must be connected to the Internet or

intranet– Middleware

• Adobe ColdFusion

• Data Security– Well-designed systems provide security at three

levels: the database itself, the Web server, and the telecommunication links that connect the components of the system

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Data Design Terminology

• Definitions– Entity– Table or file– Field– Record

• Tuple

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Data Design Terminology

• Key Fields– Primary key– Candidate key– Foreign key– Secondary key

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Data Design Terminology

• Referential Integrity– Validity checks can help

avoid data input errors– In a relational database,

referential integrity means that a foreign key value cannot be entered in one table unless it matches an existing primary key in another table

– Orphan

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Entity-Relationship Diagrams

• Drawing an ERD– The first step is to list the

entities that you identified during the fact-finding process and to consider the nature of the relationships that link them

– A popular method is to represent entities as rectangles and relationships as diamond shapes

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Entity-Relationship Diagrams

• Types of Relationships– Three types of

relationships can exist between entities

– One-to-one relationship (1:1)

– One-to-many relationship (1:M)

– Many-to-many relationship (M:N)

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Entity-Relationship Diagrams

• Cardinality• Cardinality notation• Crow’s foot notation• Unified Modeling

Language (UML)• Now that you understand

database elements and their relationships, you can start designing tables

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Normalization

• Standard Notation Format– Designing tables is easier if you use a standard

notation format to show a table’s structure, fields, and primary key

– Example: NAME (FIELD 1, FIELD 2, FIELD 3)

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Normalization

• Repeating Groups and Unnormalized Design– Repeating groups• Often occur in manual documents prepared by users

– Unnormalized– Enclose the repeating group of fields within a

second set of parentheses

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Normalization

• First Normal Form– A table is in first normal form (1NF) if it does not

contain a repeating group– To convert, you must expand the table’s primary

key to include the primary key of the repeating group

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Normalization

• Second Normal Form– A table design is in second normal form (2NF) if it is in

1NF and if all fields that are not part of the primary key are functionally dependent on the entire primary key

– A standard process exists for converting a table from 1NF to 2NF

– The objective is to break the original table into two or more new tables and reassign the fields so that each nonkey field will depend on the entire primary key in its table

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Normalization

• Third Normal Form– 3NF design avoids redundancy and data integrity

problems that still can exist in 2NF designs– A table design is in third normal form (3NF) if it is

in 2NF and if no nonkey field is dependent on another nonkey field

– To convert the table to 3NF, you must remove all fields from the 2NF table that depend on another nonkey field and place them in a new table that uses the nonkey field as a primary key

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Normalization

• A Normalization Example

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Using Codes During Data Design

• Overview of Codes– Because codes often are used to represent data,

you encounter them constantly in your everyday life

– They save storage space and costs, reduce data transmission time, and decrease data entry time

– Can reduce data input errors

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Using Codes During Data Design

• Types of Codes1. Sequence codes2. Block sequence codes3. Alphabetic codes4. Significant digit codes5. Derivation codes6. Cipher codes7. Action codes

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Using Codes During Data Design

• Developing a Code1. Keep codes concise2. Allow for expansion3. Keep codes stable4. Make codes unique5. Use sortable codes

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Using Codes During Data Design

• Developing a Code6. Avoid confusing codes7. Make codes meaningful8. Use a code for a single purpose9. Keep codes consistent

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Database Design: One Step At a Time1. Create an initial ERD2. Next, create an ERD3. Review all the data elements4. Review the 3NF designs for all tables5. Double-check all data dictionary entries• After creating your final ERD and normalized

table designs, you can transform them into a database

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Database Models

• A Real-World Business Example– Imagine a company that

provides on-site service for electronic equipment, including parts and labor

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Database Models

• Working with a Relational Database– To understand the power and flexibility of a

relational database, try the following exercise– Suppose you work in IT, and the sales team needs

answers to three specific questions– The data might be stored physically in seven tables

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Data Storage and Access

• Data storage and access involve strategic business tools

• Strategic tools for data storage and access– Data warehouse –

dimensions– Data mart– Data Mining

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Data Storage and Access

• Logical and Physical Storage– Logical storage• Characters • Data element or data item• Logical record

– Physical storage• Physical record or block• Buffer• Blocking factor

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Data Storage and Access

• Data Coding and Storage– Binary digits– Bit– Byte– EBCDIC, ASCII, and

Binary– Unicode

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Data Storage and Access

• Data Coding and Storage– Storing dates• Y2K Issue• Most date formats now are based on the model

established by the International Organization for Standardization (ISO)• Absolute date

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Data Control

• User ID• Password• Permissions• Encryption• Backup• Recovery procedures• Audit log files• Audit fields

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Chapter Summary

• Files and tables contain data about people, places, things, or events that affect the information system

• DBMS designs are more powerful and flexible than traditional file-oriented systems

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Chapter Summary

• An entity-relationship (ERD) is a graphic representation of all system entities and the relationships among them

• A code is a set of letters or numbers used to represent data in a system

• The most common database models are relational and object-oriented

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Chapter Summary

• Logical storage is information seen through a user’s eyes, regardless of how or where that information actually is organized or stored

• Physical storage is hardware-related and involves reading and writing blocks of binary data to physical media

• File and database control measures include limiting access to the data, data encryption, backup/recovery procedures, audit-trail files, and internal audit fields

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Chapter Summary

• Chapter 9 complete

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