Download Data Design

Systems Analysis & Design
7th Edition
Chapter 8
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 entityrelationship 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 Webbased 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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Data Design Concepts
 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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Data Design Concepts
 Overview of File Processing
– Various types of files
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Master file stores permanent data about an entity
Table file contains referenced data used by system
Transaction file stores day to day operational data
Work file temporary file created by system for single task
Security file created for backup and recovery
History file created for archiving purposes
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Data Design Concepts
 The Evolution from File Systems to Database
Systems
– Advantages
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Scalability
Better support for client/server systems
Economy of scale better utilization of hardware
Flexible data sharing allowing user to see the
same data in different way
• Enterprise-wide application – database
administrator (DBA) managing database for the
benefit of orgnization
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Data Design Concepts
 The Evolution from File Systems to Database
Systems
• Stronger standards for data name, formats and
documentation
• Controlled redundancy
• Better security
• Increased programmer productivity
• Data independence
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Data Design Concepts
 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, including
storing, retrieving, updating and deleting
data
 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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Web-Based Database Design
 Characteristics of Web-Based Design
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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
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Web-Based Database Design
 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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Data Design Terminology
 Key Fields
– Primary key
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Combination key
Composite key
Concatenated key
Multi-valued key
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Data Design Terminology
 Key Fields
– Candidate key
• Nonkey field
– 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)
• Associative entity
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Entity-Relationship Diagrams
 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 2NF
1. 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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Using Codes During System Design
 Types of Codes
1. Sequence codes
number or letter assigned in specific order
employee number assigned by the other order they hired
2. Block sequence like
codes college course numbers
3. Alphabetic codes
a. Category codes
like HW for the hardware department in the store
b. Abbreviation codes – mnemonic codes like
department code CSIS
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Using Codes During System Design
 Types of codes
4. Significant digit codes like zip code
5. Derivation codes like magazine’s subscriber code
6. Cipher codes use key word to encode number
7. Action codes for example D for delete, A for add
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Using Codes During System Design
 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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Using Codes During System Design
 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.
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Create the initial ERD
Assign all data elements to entities
Create 3NF designs for all tables
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 objectoriented 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 – is a collection of data that can include
information, no matter where it is stored. Since it can link data it needs to
have support management analysis
– Data mart includes data that users in that department require to
perform their jobs
– Data mining software that looks for meaningful patterns and
relationships among data
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Data Storage and Access
 Logical and Physical Storage
– Logical storage
• Basic element of data are Characters
• Groups of characters forms a filed, a filed also called data
element or data item
• Logical record set of filed that describes a person, place or
things
– Physical storage
• Physical record or block smallest data unit that can be
handle by OS
• Buffer system reads data from records to buffer, part of
memory to process the data
• Blocking factor the actual number of logical records in a
physical records determined by blocking factor.
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Data Storage and Access
 Data Storage Formats
– Binary digits
– Bit
– Byte
– EBCDIC and ASCII represent character in
byte
– Unicode – internationalize represent
character in 16 bits
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Data Storage and Access
 Data Storage Formats
– Binary
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Binary storage format
Integer format
Long integer format
Other binary formats exist for efficient storage of
exceedingly long numbers
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Data Storage and Access
 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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Data Storage and Access
 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
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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
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