Systems Analysis & Design 7 th Edition Chapter 8.

Systems Analysis & Design

7th Edition

Chapter 8

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Chapter Objectives

Explain data design concepts and data structures

Describe file processing systems Explain database systems and define the

components of a database management system (DBMS)

Describe Web-based data design

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Chapter Objectives

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 Explain the importance of codes and describe

various coding schemes

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Chapter Objectives

Describe relational and object-oriented database models

Explain data warehousing and data mining Differentiate between logical and physical

storage and records Explain data control measures

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Introduction

You will develop a physical plan for data organization, storage, and retrieval

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

– A file or table contains data about people, places or events that interact with the system

– File-oriented system

– File processing

– Database system

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Overview of File Processing

– Can be more efficient and cost-effective in certain situations

– Potential problems • Data redundancy

• Data integrity

• Rigid data structure

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Overview of File Processing

– Various types of files• Master file

• Table file

• Transaction file

• Work file

• Security file

• History file

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The Evolution from File Systems to Database Systems– Advantages

• Scalability

• Better support for client/server systems

• Economy of scale

• Flexible data sharing

• Enterprise-wide application – database administrator (DBA)

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The Evolution from File Systems to Database Systems

– Advantages• Stronger standards

• Controlled redundancy

• Better security

• Increased programmer productivity

• Data independence

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Database Tradeoffs– Because DBMSs are powerful, they require

more expensive hardware, software, and data networks capable of supporting a multi-user environment

– More complex than a file processing system– Procedures for security, backup, and

recovery are more complicated and critical

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DBMS Components

Interfaces for Users, Database Administrators, and Related Systems

– Users

– Database Administrators

– Related information systems• A DBMS can support several related information

systems that provide input to, and require specific data from, the DBMS

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DBMS Components

Data Manipulation Language

– A data manipulation language (DML) controls database operations

Schema

– The complete definition of a database, including descriptions of all fields, tables, and relationships

– 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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Internet Terminology

– Web browser

– Web page

– HTML (Hypertext Markup Language)

– Tags

– Web server

– Web site

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Internet Terminology

– Intranet

– Extranet

– Protocols

– Web-centric

– Clients

– Servers

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Connecting a Database to the Web

– Database must be connected to the Internet or intranet

• Middleware

• Adobe

ColdFusion

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Data Security

– Web-based data must be totally secure, yet easily accessible to authorized users

– To achieve this goal, 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• Attribute

• Common field

– Record• Tuple

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Key Fields

– Primary key• Combination key

• Composite key

• Concatenated key

• Multi-valued key

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Key Fields

– Candidate key• Nonkey field

– Foreign key

– Secondary key

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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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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)• Associative entity

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Cardinality• Cardinality

notation

• Crow’s foot notation

• Unified Modeling Language (UML)

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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 group• Often occur in manual documents prepared by

users

– Unnormalized

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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 standard process exists for converting a table from 1NF to 2NF1. First, create and name a separate table for each

field in the existing primary key

2. Next, create a new table for each possible combination of the original primary key fields

3. Finally, study the three tables and place each field with its appropriate primary key

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Normalization

Second Normal Form

– Four kinds of problems are found with 1NF description that do not exist with 2NF

• Consider the work necessary to change a particular product’s design

• 1NF tables can contain inconsistent data

• Adding a new product is a problem

• Deleting a product is a problem

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Normalization

Third Normal Form

– 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 System 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 transmission time, and decrease data entry time

– Can reduce data input errors

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Types of Codes

1. Sequence codes

2. Block sequence codes

3. Alphabetic codesa. Category codes

b. Abbreviation codes – mnemonic codes

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Types of codes

4. Significant digit codes

5. Derivation codes

6. Cipher codes

7. Action codes

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Developing a Code

1. Keep codes concise

2. Allow for expansion

3. Keep codes stable

4. Make codes unique

5. Use sortable codes

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Developing a Code

6. Avoid confusing codes

7. Make codes meaningful

8. Use a code for a single purpose

9. Keep codes consistent

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Steps in Database Design

1. Create the initial ERD

2. Assign all data elements to entities

3. Create 3NF designs for all tables

4. Verify 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

Relational Databases– The relational model was introduced during

the 1970s and became popular because it was flexible and powerful

Object-Oriented Databases

– Many systems developers are using object-oriented database (OODB) design as a natural extension of the object-oriented analysis process

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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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Logical and Physical Storage

– Logical storage• Characters

• Date element or data item

• Logical record

– Physical storage• Physical record or block

• Buffer

• Blocking factor

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Data Storage Formats

– Binary digits

– Bit

– Byte

– EBCDIC and ASCII

– Unicode - internationalize

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Data Storage Formats

– Binary• Binary storage format

• Integer format

• Long integer format

• Other binary formats exist for efficient storage of exceedingly long numbers

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Selecting a Data Storage Format

– In many cases, a user can select a specific data storage format

– For example, when using Microsoft Office, you can store documents, spreadsheets, and databases in Unicode-compatible form by using the font called Arial Unicode MS

– Best answer is it depends on the situation

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Date Fields– Most date formats now are based on the model

established by the International Organization for Standardization (ISO)

– Can be sorted easily and used in comparisons– Absolute date– Best method depends on how the specific date

will be printed, displayed or used in a calculation

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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

Data design tasks include creating an initial ERD; assigning data elements to an entity; normalizing all table designs; and completing the data dictionary entries for files, records, and data elements

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

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

Chapter 8 complete

Systems Analysis & Design 7 th Edition Chapter 8.

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Transcript of Systems Analysis & Design 7 th Edition Chapter 8.