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:

– 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

DatabaseDatabase

FilesFiles

RecordsRecords

FieldsFields

Characters(bytes)

Characters(bytes)

Personel file

Department file

Payroll file

(Project database)

005-10-6321 Johns Francine 10-7-65549-77-1001 Buckley Bill 2-17-79098-40-1370 Fiske Steven 1-5-85

(Personnel file)

098-40-1370 Fiske Steven 1-5-85 598 (Record containing SSN, last name, first name, date of hire)

Fiske (Last name field)

1000100 (Letter ‘F’ in ASCII)

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

Key field Attributes (fields)Entities(records)

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

The Traditional Approach• The traditional approach…

– Separate files are created and stored for each application program

PayrollPayroll

programsReports

Data FilesApplicationprograms Users

InvoicingInvoicingprograms

Reports

Inventorycontrol

Inventorycontrol

programs

Reports

Managementinquiries

Managementinquiriesprograms

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 data

Inventorydata

InvoicingData

Otherdata

Databasemanagement

system

Payrollprogram

Inventoryprogram

Invoicingprogram

Otherprograms

Reports

Reports

Reports

Reports

Database Interface Applications programs Users

Advantages

– 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

IdNumberFisrtNameLastName

PRODUCT

IdProdNameColour

Order1,n 1,n

relationship

entities

attributes

Hierarchical Database Model• Hierarchical database model

– A data model in which data are organized in a top-down, or inverted tree structure

Department C

Employee1

Employee2

Employee3

Employee4

Employee5

Employee6

Department B

Project 1

Department A

Network Data Model

• Network data model• An expansion of the hierarchical database model with

an owner-member relationship in which a member may have many owners

Project 1 Project 2

Department A 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

Project Number

Description

Dept. Number

155 Payroll 257

498 Widgets 632

226 Sales

manager598

Dept. Number

Dept. Name

Manager SSN

257 Accounting421-55-99993

632Manufactur

ing765-00-

3192

598 Marketing098-40-

1370

SSN Last Name First Name Hire DateDept.

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

Data Table 1: Project Table Data Table 2: Department Table

Data Table 3: Manager Table

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

DescriptionDept.

Number

155 Payroll 257

498 Widgets 632

226 Sales

manager598

Dept. Number

Dept. NameManager

SSN

257 Accounting421-55-99993

632Manufacturi

ng765-00-3192

598 Marketing 098-40-1370

SSNLast

NameFirst 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