Systems Analysis and Design 8th Edition

Chapter 9Data Design

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– Each file or table

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

– File-oriented systemor File processing system

– Database system

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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• Data dependence• 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• Economy of scale• Enterprise-wide application – database administrator

(DBA)• Controlled redundancy• Data independence

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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

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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 (Pg. 402)– 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 (Pg. 405)• 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 (Pg. 407)– 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 (Pg. 410)– 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 fully 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 (Ppg. 411 - 412)– 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 (transitional dependency)

– 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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Standard notation formats?

Normalization

• Solve for Third Normal Form– Use standard notation format

Stud. Stud. Campus Major Course Course Instr Instr Instr GradeID Name Address ID Title ID Name Location

Normalization

• Solve for Third Normal FormStud. Stud. Campus Major Course Course Instr Instr Instr GradeID Name Address ID Title ID Name Location

STUDENT (STUDENT_ID, STUDENT_NAME, CAMPUS_ADDRESS, MAJOR, INSTR_ID)COURSE (COURSE_ID, COURSE_TITLE, INSTR_ID)INSTRUCTOR (INSTR_ID, INSTR_NAME, INSTR_LOCATION)GRADES (STUDENT_ID, COURSE_ID, GRADE)

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 codes (379)2. Block sequence codes

(MSIT3050)3. Alphabetic codes (MA)4. Significant digit codes

(01610)5. Derivation codes (magazine

subscriber code)6. Cipher codes (letters

represent numbers)7. Action codes (“D” to

Display)

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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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Steps in Database Design

1. Create the initial ERD2. Assign all data elements to entities3. Create 3NF designs for all tables4. 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

– Because all the tables are linked, a user can request data that meets specific conditions

– New entities and attributes can be added at any time without restructuring the entire database

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Database Models

• Object-Oriented Databases– Many systems

developers are using object-oriented database (OODB) design

• Object Management Group (OMG)

• Each object has a unique object identifier

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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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