Transcript Diapositive 1

Information Systems
Chapter 2
Organizing Data and Information
Data
• Data
– A necessity for almost any enterprise to carry out its business.
Consists of raw facts, and when organized may be
transformed into information
• Database
– A collection of data organized to meet users’ needs
• Database management system (DBMS)
– A group of programs that manipulate the database and
provide an interface between the database and the user of the
database or other application programs
DBMS ‘Discussion’ (1)
A collection of programs that enables you to store, modify, and
extract information from a database. There are many different types
of DBMSs, ranging from small systems that run on personal
computers to huge systems that run on mainframes. The following
are examples of database applications:
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computerized library systems
automated teller machines
flight reservation systems
computerized parts inventory systems
From a technical standpoint, DBMSs can differ widely. The terms
DBMS ‘Discussion’ (2)
relational, network, flat, and hierarchical all refer to the way a
DBMS organizes information internally. The internal organization can
affect how quickly and flexibly you can extract information.
Requests for information from a database are made in the form of a
query, which is a stylized question. For example, the query
SELECT ALL WHERE NAME = "SMITH" AND AGE > 35
requests all records in which the NAME field is SMITH and the AGE
DBMS ‘Discussion’ (3)
field is greater than 35. The set of rules for constructing queries is
known as a query language. Different DBMSs support different query
languages, although there is a semi-standardized query language
called SQL (structured query language). Sophisticated languages for
managing database systems are called fourth-generation languages,
or 4GLs for short.
The information from a database can be presented in a variety of
formats. Most DBMSs include a report writer program that enables
you to output data in the form of a report. Many DBMSs also include
DBMS ‘Discussion’ (4)
a graphics component that enables you to output information in the
form of graphs and charts.
Hierarchy of data
Hierarchy of Data
Example
Personel file
Database
Department file
(Project database)
Payroll file
Files
005-10-6321 Johns Francine 10-7-65
549-77-1001 Buckley Bill 2-17-79
098-40-1370 Fiske Steven 1-5-85
Records
098-40-1370 Fiske Steven 1-5-85 598
Fields
Fiske
Characters
(bytes)
1000100
(Last name field)
(Letter ‘F’ in ASCII)
(Personnel file)
(Record containing
SSN, last name,
first name, date of
hire)
Terminology
• Database
• A collection of integrated and related files
• File
• A collection of related records
• Record
• A collection of related fields
• Field
• A group of characters
• Character
• Basic building block of information, represented by a byte
Data Entities, Attributes, and Keys
• Entity
• A generalized class of people, places, or things (objects) for which
data are collected, stored, and maintained
• E.g., Customer, Employee
• Attribute
• A characteristic of an entity; something the entity is identified by
• E.g., Customer name, Employee name
• Keys
• A field or set of fields in a record that is used to identify the record
• E.g, A field or set of fields that uniquely identifies the record
Keys and Attributes
Employee #
Last name
First name
Hire date
Dept. #
005-10-6321
Johns
Francine
10-7-65
257
549-77-1001
Buckley
Bill
2-17-79
650
098-40-1370
Fiske
Steven
1-5-85
598
Key field
Attributes (fields)
Entities
(records)
The Traditional Approach
• The traditional approach…
– Separate files are created and stored for each application program
Data
Files
Application
programs
Users
Payroll
Payroll
programs
Reports
Invoicing
Invoicing
programs
Reports
Inventory
control
Inventory
control
programs
Reports
Management
inquiries
Management
inquiries
programs
Reports
Drawbacks
• Data redundancy
– Duplication of data in separate files
• Lack of data integrity
– The degree to which the data in any one file is
accurate
• Program-data dependence
– A situation in which program and data organized for
one application are incompatible with programs and
data organized differently for another application
Database Approach
• The database approach…
– A pool of related data is shared by multiple
application programs
– Rather than having separate data files, each
application uses a collection of data that is either
joined or related in the database
Payroll
program
Reports
Inventory
program
Reports
Invoicing
program
Reports
Payroll data
Inventory
data
Invoicing
Data
Database
management
system
Other
data
Database
Interface
Other
programs
Reports
Applications programs
Users
Advantages
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Improved strategic use of corporate data
Reduced data redundancy
Improved data integrity
Easier modification and updating
Data and program independence
Better access to data and information
Standardization of data access
A framework for program development
Better overall protection of the data
Shared data and information resources
Disadvantages
– Relatively high cost of purchasing and operating a
DBMS in a mainframe operating environment
– Increased cost of specialized staff
– Increased vulnerability
Data Modeling and
Database Models (1)
• Planned data redundancy
– A way of organizing data in which the logical
database design is altered so that certain data entities
are combined
– Summary totals are carried in the data records rather
than calculated from elemental data
– Some data attributes are repeated in more than one
data entity to improve database performance
Data Modeling and
Database Models (2)
• Data model
– A map or diagram of entities and their relationships
• Enterprise data modeling
– Data modeling done at the level of the entire
organization
• Entity-relationship (ER) diagrams
– A data model that uses basic graphical symbols to
show the organization of and relationships between
data
Example:
Entity Relationship (ER) Diagram for a Customer
Ordering Database
CUSTOMER
IdNumber
FisrtName
LastName
PRODUCT
1,n
Order
relationship
entities
attributes
1,n
IdProd
Name
Colour
Hierarchical Database Model
• Hierarchical database model
– A data model in which data are organized in a top-down, or inverted tree
structure
Project 1
Department A
Employee
1
Employee
2
Department B
Employee
3
Employee
4
Department C
Employee
5
Employee
6
Network Data Model
• Network data model
• An expansion of the hierarchical database model with an ownermember relationship in which a member may have many owners
Project 1
Department A
Project 2
Department B
Department C
Relational Data Model
• Relational data model
– All data elements are placed in two-dimensional tables, called
relations, that are the logical equivalent of files
Data Table 2: Department Table
Data Table 1: Project Table
Project Number
Description
Dept. Number
Dept. Number
Dept. Name
Manager SSN
155
Payroll
257
257
Accounting
421-55-99993
498
Widgets
632
632
Manufacturing
765-00-3192
226
Sales manager
598
598
Marketing
098-40-1370
Data Table 3: Manager Table
SSN
Last Name
First Name
Hire Date
Dept. Number
005-10-6321
Johns
Francine
10-7-65
257
549-77-1001
Buckley
Bill
2-17-79
650
098-40-1370
Fiske
Steven
1-5-85
598
Relational Database Terminology
• Selecting
– Data manipulation that eliminates rows according to
certain criteria
• Projecting
– Data manipulation that eliminates columns in a table
• Joining
– Data manipulation that combines two or more tables
• Linked
– Relating tables in a relational database together
Linking Data Tables to Answer an
Inquiry
Project Number
Description
Dept. Number
155
Payroll
257
498
Widgets
632
226
Sales manager
598
Dept. Number
Dept. Name
Manager SSN
257
Accounting
421-55-99993
632
Manufacturing
765-00-3192
598
Marketing
098-40-1370
SSN
Last Name
First Name
Hire Date Dept. Number
005-10-6321
Johns
Francine
10-7-65
257
549-77-1001
Buckley
Bill
2-17-79
650
098-40-1370
Fiske
Steven
1-5-85
598