Systems Analysis & Design 7 Edition Chapter 8

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
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
– Advantages
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Scalability
Better support for client/server systems
Economy of scale
Flexible data sharing
Enterprise-wide application – database
administrator (DBA)
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Data Design Concepts
 The Evolution from File Systems to Database
Systems
– Advantages
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Stronger standards
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
 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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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
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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
2. Block sequence codes
3. Alphabetic codes
a. Category codes
b. Abbreviation codes – mnemonic codes
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Using Codes During System Design
 Types of codes
4. Significant digit codes
5. Derivation codes
6. Cipher codes
7. Action codes
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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.
2.
3.
4.
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 – dimensions
– Data mart
– Data mining
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Data Storage and Access
 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 and Access
 Data Storage Formats
– Binary digits
– Bit
– Byte
– EBCDIC and ASCII
– Unicode - internationalize
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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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