systems analysis & design 7 th edition chapter 8
TRANSCRIPT
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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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• 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
• 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• 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• 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 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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Using Codes During System Design
Types of Codes
1. Sequence codes
2. Block sequence codes
3. Alphabetic codesa. 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. 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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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• 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
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