Systems Analysis & Design (Sixth Edition) 1 Chapter 7 Data Design PHASE 3: SYSTEMS DESIGN

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Systems Analysis & Design(Sixth Edition)

Chapter 7Data Design

PHASE 3: SYSTEMS DESIGN

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Chapter Objectives

Explain data design concepts and data structures Describe file processing systems and various

types of files Understand 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 control

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Data Design Concepts

Data Structures A file or table contains data about people, places,

things, or events that interact with the system File-oriented system File processing system Database system

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Overview of File Processing Potential problems

Data redundancy Data integrity Rigid data structure

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Overview of File Processing Uses various types of files

Master file Table file Transaction file Work file – scratch file Security file History file

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Overview of Database Systems A properly designed database system offers a

solution to the problems of file processing Provides an overall framework that avoids data

redundancy and supports a real-time, dynamic environment

Database management system (DBMS) The main advantage of a DBMS is that it offers

timely, interactive, and flexible data access

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Overview of Database Systems 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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Overview of Database Systems Advantages

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 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

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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 In a Web-based design, the Internet serves as

the front end, or interface, for the database management system

Internet technology provides enormous power and flexibility

Web-based systems are popular because they offer ease of access, cost-effectiveness, and worldwide connectivity

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

intranet Middleware Macromedia’s 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: 1. The database itself

2. The Web server

3. 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

Composite key (aka Combination key , Concatenated key, Multi-valued key)

Candidate key Nonkey field

Foreign key Secondary key

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Referential Integrity Validity checks can help avoid data input errors

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Entity-Relationship Diagrams

An entity is a person, place, thing, or event for which data is collected and maintained

Provides an overall view of the system, and a blueprint for creating the physical data structures

Entity-relationship diagram

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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

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Types of Relationships 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

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Normalization

Table design Involves four stages: unnormalized design,

first normal form, second normal form, and third normal form

Most business-related databases must be designed in third normal form

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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 Designs Repeating group

Often occur in manual documents prepared by users Unnormalized design

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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 Second Normal Form

To understand second normal form (2NF), you must understand the concept of functional dependence

Functionally dependent

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Normalization

Second Normal Form A standard process exists for converting a table

from 1NF to 2NF• Create and name a separate table for each field in

the existing primary key• Create a new table for each possible combination

of the original primary key fields• 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 designs

that do not exist in 2NF Consider the work necessary to change a particular

product’s description 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 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 To show the

normalization process, consider the familiar situation, which depicts several entities in a school advising system: ADVISOR, COURSE, and STUDENT

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Steps in Database Design

• Create the initial ERD• Assign all data elements to entities• Create 3NF designs for all tables, taking care

to identify all primary, secondary, and foreign keys

• 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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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

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

Any questions?

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Systems Analysis & Design (Sixth Edition) 1 Chapter 7 Data Design PHASE 3: SYSTEMS DESIGN