Kap 1 Engelsk

8/9/2019 Kap 1 Engelsk

1/50

2008 Pearson Education, Inc. All rights reserved.

1

1

1

Introduction toComputers and

the Internet


2/50


3/50


3

OBJECTIVESIn this chapter you will learn:

Basic computing concepts.

The different types of programminglanguages.

The evolution of the Internet and the WorldWide Web.

What Web 2.0 is and why its having suchan impact among Internet-based andtraditional businesses.

What Rich Internet Applications (RIAs) areand the key software technologies used to

build RIAs.


4/50


4

1.1 Introduction

1.2 What Is a Computer?1.3 Computer Organization

1.4 Machine Languages, Assembly Languages and High-LevelLanguages

1.5 History of the Internet and World Wide Web1.6 World Wide Web Consortium (W3C)

1.7 Web 2.0

1.8 Personal, Distributed and Client/Server Computing

1.9 Hardware Trends1.10 Key Software Trend: Object Technology

1.11 JavaScript: Object-Based Scripting for the Web

1.12 Browser Portability

1.13 C, C++ and Java1.14 BASIC, Visual Basic, Visual C++, C# and .NET

1.15 Software Technologies

1.16 Notes about Internet & World Wide Web How to Program,4/e

1.17 Web Resources


5/50


5

1.1 IntroductionInternet and World Wide Web How to Program: 4/e

Walkthrough of Web 2.0

Emphasizes structured programming and object-based

programming

Live-code approach

- All concepts presented in full working program examples

- Examples available at.

JavaScript, XHTML and CSS

- Introduced in earlier chapters

- Provides solid foundation for computer programming and

rest of book


6/50


6

1.1 Introduction (Cont.)Software

Instructions to command the computer to perform actions and make

decisions)

JavaScript and PHP are popular software development languages for

web-based applications.

Computer development

Computer use increasing in most fields

Computer costs and size decreasing

- Abundance of silicon drives down prices of silicon-chip technology

Applications of this book

Prepares for higher learning in C++, Java, C#, Visual Basic.NET as wellas object-oriented programming

Allows development of applications with graphical user interfaces

(GUIs)

- Multimedia capabilities

- Integration with the Internet and World Wide Web


7/50


7

1.1 Introduction (Cont.)

Apply database technologies

Applications that are not limited to the desktop

Portability

- Multiple platforms (i.e., different types of computers runningdifferent operating systems).

Book structure Focus on Web 2.0 and rich Internet applications

Chapters 1-20- Covers XHTML, JavaScript, Dynamic HTML, Extensible Markup

Language (XML), CSS, Flash, Flex, Silverlight and Dreamweaver

- For applications running on client side (typically Mozilla Firefox 2and Microsoft Internet Explorer 7)

Chapters 21-28- Cover web servers, databases, PHP, Ruby on Rails, ASP.NET,

ASP.NET Ajax and JavaServer Faces (JSF)


8/50


8

Fig. 1.1 | Architecture of Internet & World Wide Web How to Program, 4/e.


9/50


9

1.2 What is a Computer?Computer

Device capable of

- Performing computations

- Making logical decisions

Works billions of times faster than human beings

Fastest supercomputers today

- Perform hundreds of billions of additions per second


10/50


10

Programs

Sets of instructions that process data

Guide computer through orderly sets of actions specified

by computer programmers

Computer system

Comprised of various hardware devices

- Keyboard

- Screen

- Disks- Memory

- DVD drives

- Processing Units

1.2 What is a Computer? (Cont.)


11/50


11

Every computer divided into six units

1. Input unit

- Receiving section of computer- Obtains data from input devices

Usually a keyboard, mouse, disk, scanner, uploads (photosand videos) and networks (Internet)

- Places data at disposal of other units2. Output unit

- Shipping section of computer

- Puts processed info on various output devices

Screens, paper printouts, speakers

- Makes info available outside the computer (e.g., Internet)

1.3 Computer Organization


12/50


12

3. Memory unit

- Rapid access, low capacity warehouse

- Retains information entered through input unit- Retains info that has already been processed until can be sent

to output unit

- Often called memory, primary memory, or random access

memory (RAM)

4. Arithmetic and Logic Unit

- Manufacturing section of computer

- Performs calculations (addition, subtraction, multiplicationand division)

- Contains decision mechanisms and can make comparisons

1.3 Computer Organization (Cont.)


13/50


13

5. Central Processing Unit (CPU)

- Administrative section of computer

- Coordinates and supervises other sections- Multiple CPUs (multiprocessors)

6. Secondary storage unit

- Long-term, high-capacity warehouse

- Stores programs or data not currently being used by other

units on secondary storage devices (like CDs and DVDs)

- Takes longer to access than primary memory

1.3 Computer Organization (Cont.)


14/50


14

1.4 Machine Languages, Assembly

Languages and High-LevelLanguages

Three general types of programming languages

Machine languages

Assembly languages

High-level languages


15/50


15

Machine languages

Natural language of a computer (aka object code)

Defined by hardware design of computer

Generally consists of strings of numbers

Are machine dependent Cumbersome for humans

- Example: Adding overtime pay to base pay and storing the

result in gross pay

Slow and tedious for most programmers


Languages and High-LevelLanguages (Cont.)


16/50


16

Assembly languages Programmers began using English-like abbreviations to

substitute for machine languages

Represents elementary operations of computer

Translator programs called assemblers convert assembly-

language to machine-language

Example:

!# !# !# !#$#$#$#$#

&%' "#&%' "#&%' "#&%' "#


Languages and High-LevelLanguages (Cont.)


17/50


17

High-level languages Developed as computer usage increased, assembly

language proved inadequate and time-consuming

Single statements can be written to accomplish substantial

tasks

Translator programs called compilers

Allow programmers to write instructions almost like

every-day English Example:

()"+,*"+-)&"+()"+,*"+-)&"+()"+,*"+-)&"+()"+,*"+-)&"+

1.4 Machine Languages, Assembly Languages

and High-Level Languages (Cont.)


18/50


18

High-level languages (II)

Much more desirable from programmers standpoint

Specific languages include

- C, C++, Visual Basic.NET, C# and Java

- Among most powerful and widely used languages today

Interpreter programs developed to execute high-level programswithout compiling

- Popular in program development environments

Once program developed, compiled version made

In this book, several key programming languages

- JavaScript, ActionScript, PHP and Ruby on Railseach of these

scripting languages is processed by interpreters

Study markup languages

- XHTML and XML, which can be processed by interpreted scriptinglanguages

- Achieve their goal of portability across a variety of platforms

1.4 Machine Languages, Assembly Languages

and High-Level Languages (Cont.)


19/50


19

Performance Tip 1.1

Interpreters have an advantage overcompilers in scripting. An interpretedprogram can begin executing as soon as it isdownloaded to the clients machine, without

the need to be compiled before it can execute.On the downside, scripts generally run muchslower than compiled code.


20/50


20

Portability Tip 1.1

Interpreted languages are more portable thancompiled languages. Interpreters can be

implemented for each platform on which theinterpreted languages need to execute.


21/50


21

Software Engineering Observation 1.1

Interpreted languages are more dynamic thancompiled languages. For example, server-sideapplications can generate code in response to

user interactions, and that code can then beinterpreted in a browser.


22/50


22

1.5 History of the Internet and World

Wide WebARPANET

Implemented in late 1960s by ARPA (Advanced Research

Projects Agency of DOD)

Networked computer systems of a dozen universities and

institutions with 56KB communications lines

Grandparent of todays Internet Intended to allow computers to be shared

Became clear that key benefit was allowing fast

communication between researchers electronic-mail

(email)


23/50


23


Wide WebARPAs goals Allow multiple users to send and receive info at same time

Network operated packet switching technique- Digital data sent in small packages called packets

- Packets contained data, address info, error-control info and

sequencing info

- Greatly reduced transmission costs of dedicatedcommunications lines

Network designed to be operated without centralized

control

- If portion of network fails, remaining portions still able to

route packets


24/50


24


Wide WebTransmission Control Protocol (TCP)

Name of protocols for communicating over ARPAnet

Ensured that messages were properly routed and that theyarrived intact

Organizations implemented own networks

Used both for intra-organization and communication

25


25/50


25


Wide WebHuge variety of networking hardware and softwareappeared

ARPA achieved inter-communication between all platformswith development of the IP

- Internetworking Protocol

- Current architecture of Internet

Combined set of protocols called TCP/IP

The Internet

Limited to universities and research institutions

Military became big user

Next, government decided to access Internet for commercial

purposes

26


26/50


26


Wide WebInternet traffic grew Businesses spent heavily to improve Internet

- Better service their clients

Fierce competition among communications carriers and hardwareand software suppliers

Resulted in massive bandwidth increase and plummeting costs

Tim Berners-Lee invents HyperText Markup Language (HTML)

- Also writes communication protocols to form the backbone newinformation system = World Wide Web

- Hypertext Transfer Protocol (HTTP)a communications protocol usedto send information over the web

Web use exploded with availability in 1993 of the Mosaic browser

Marc Andreessen founds Netscape

- Company many credit with initiating the explosive Internet of late 1990s.

27


27/50


27

1.6 World Wide Web Consortium

(W3C)W3C Founded in 1994 by Tim Berners-Lee

Homepage at

Goals Internet universally accessible

Standardization

- W3C Recommendations:Technologies standardized by W3C

include the Extensible HyperText Markup Language(XHTML), Cascading Style Sheets (CSS), HyperTextMarkup Language (HTMLnow considered a legacytechnology) and the Extensible Markup Language(XML).

not an actual software product, but a document thatspecifies a technologys role, syntax rules and so forth.

28


28/50


28

1.7 Web 2.0

2003 noticeable shift in how people and businesses were using the weband developing web-based applications

The term Web 2.0 was coined by Dale Dougherty of OReilly

Web 2.0 definition = companies use the web as a platform to createcollaborative, community-based sites (e.g., social networking sites, blogs,wikis, etc.).

Web 1.0 (1990s and early 2000s) focused on a small number ofcompanies and advertisers producing content for users to access

brochure web)Web 2.0 involves the

Web 1.0 is as a lecture,

Web 2.0 is a conversation

Websites like MySpace , Facebook , Flickr , YouTube, eBay and

Wikipedia , users create the content, companies provide theplatforms.

29


29/50


29

1.7 Web 2.0 (Cont.)

Architecture of participation

Open source software

Collective

Rich Internet Applications (RIAs)

Software as a Service (SaaS)

Web services incorporate functionality fromexisting applications and websites into own web

applications

Amazon Web Services

Maps web services with eBay web services

30


30/50


30

1.7 Web 2.0 (Cont.)

Future computers learn to understand the

meaning of the data on the web = Semantic Web

Deitel Web 2.0 Resource Center at

www.deitel.com/web2.0/for more information.

31


31/50


1.8 Personal, Distributed and

Client/Server Computing1977 Apple Computer popularized personal computing

Computers became economical for personal or business use

Machines could be linked together in computer networks

Local area networks (LANs)

Distributed computing

Workstations

Servers offer data storage and other capabilities that maybe used by client computers distributed throughout thenetwork,

Client/server computing

Popular operating systems

UNIX, Linux, Mac OS X and Microsofts Windows

32


32/50


1.9 Hardware Trends

Improving technologies

Internet community thrives on improvements of

- Hardware, Software and Communications

Cost of products and services

- Consistently dropping over the decades

Computer capacity and speed

- Doubles every two years (on average) = Moores Law

Microprocessor chip

- Laid groundwork in late 1970s and 1980s for productivity

improvements of the 1990s

Hardware moving toward mobile, wireless technology.

- Hand-held devices more powerful than early supercomputers

- Portability

- Wireless data-transfer speeds

33


33/50


1.10 The Key Software Trend:

Object Technology

Objects

Reusable software components that model items in the real

world (classes)

Makes software developers more productive

Object-oriented programs often easier to understand,correct and modify than older types of programs

34

1 10 Th K S ft T d


34/50



Object Technology (Cont.)Object technology

Packaging scheme that helps create meaningful software

units- Large and highly focused on particular applications areas

Before appeared, programming languages were focused on

actions (verbs) rather than on objects (nouns)

- Programmers would program primarily with verbs

- Made program awkward

- We live in a world filled with complex objects and simple

actions

35

1 10 The Key Software Trend:


35/50



Object Technology (Cont.)Object technology (continued)

Object-oriented programming

- Programmers work in manner similar to how they see theworld

- More natural process

- Significant productivity enhancements

Procedural programming- Not particularly reusable

- Forces programmers to constantly re-invent the wheel

Wastes time and resources

Objects (classes)- Software modules

- Kept in libraries

- Reusable save time and resources

36


36/50



Extensive class libraries of reusable softwarecomponents are available on the Internet.

Many of these libraries are free.

37


37/50



Some organizations report that the key benefit

object-oriented programming gives them is notsoftware that is reusable but, rather, softwarethat is more understandable, better organizedand easier to maintain, modify and debug. This

can be significant, because perhaps as much as 80percent of software cost is associated not with theoriginal efforts to develop the software, but with

the continued evolution and maintenance of thatsoftware throughout its lifetime.

38

1 11 JavaScript: Object Based


38/50


1.11 JavaScript: Object-Based

Scripting for the WebJavaScript Attractive package for advancing level of programming language

education

Object-based language Supports proper software engineering techniques

Free as part of todays most popular Web browsers

Powerful scripting language

- Portable- Programs execute interpretively on client machines

ActionScript and JavaScript are converging in the nextversion of the JavaScript standard (JavaScript 2/ECMAScript version 4)

- Universal client scripting language, simplifying webapplication development

39


39/50


Good Programming Practice 1.1

Write your programs in a simple andstraightforward manner. This is sometimesreferred to as KIS (keep it simple). One keyaspect of keeping it simple is anotherinterpretation of KISkeep it small. Do notstretch the language by trying bizarre us-es.

40


40/50


Portability Tip 1.2

Although it is easier to write portable

programs in JavaScript than in many otherprogramming languages, differences amonginterpreters and browsers make portability

difficult to achieve. Simply writing programsin JavaScript does not guarantee portability.Programmers occasionally need to researchplatform variations and write their code

accordingly.

41


41/50


Portability Tip 1.3

When writing JavaScript programs, you need

to deal directly with cross-browser portabilityissues. Such issues are hidden by JavaScriptlibraries (e.g., Dojo, Prototype, Script.aculo.usand ASP.NET Ajax) which provide powerful,ready-to-use capabilities that simplifyJavaScript coding by making it cross-browsercompatible.

42


42/50


Error-Prevention Tip 1.1

Always test your JavaScript programs on allsystems and in all web browsers for which

they are intended.

43


43/50


Good Programming Practice 1.2

Read the documentation for the JavaScriptversion you are using to access JavaScripts

rich collection of features.

44


44/50


Error-Prevention Tip 1.2

Your computer and JavaScript interpreterare good teachers. If you are not sure how afeature works, even after studying thedocumentation, experiment and see whathappens. Study each error or warningmessage and adjust the code accordingly.

45

1 12 B P bili


45/50


1.12 Browser Portability

Browser portability

Great challenge

- Great diversity of client browsers in use- Many different platforms also in use

Difficult to

Know capabilities and features of all browsers andplatforms in use

Find correct mix between absolute portability, complexity

and usability of features

46


46/50


Portability Tip 1.4

The web is populated with many differentbrowsers, which makes it difficult for authorsand web application developers to createuniversal solutions. The W3C is workingtoward the goal of a universal client-sideplatform.

47

1 13 C C d J


47/50


1.13 C, C++ and Java

C

developed by Dennis Ritchie at Bell Laboratories

development language of the UNIX operating system

virtually all new major operating systems are written in C and/or C++

C++ developed by Bjarne Stroustrup in early 1980s

spruce up the C language and provides capabilities for object-orientedprogramming

Java

developed by Sun Microsystems in 1991

Sun saw the immediate potential of using Java to add dynamic content (e.g.,interactivity, animations and the like) to web pages

Sun formally announced Java at an industry conference in May 1995

Java is now used to- develop large-scale enterprise applications

- enhance the functionality of web servers- provide applications for consumer devices

48

1.14 BASIC, Visual Basic, Visual C++, C#


48/50


1.14 BASIC, Visual Basic, Visual C++, C#and .NET

BASIC

Developed in the mid-1960s at Dartmouth College

Primary purpose was to familiarize novices with programming

techniquesMicrosofts Visual Basic language

Based on Basic

Has become one of the most popular programming languages in theworld

Microsofts .NET platform

Provides the capabilities developers need to create computerapplications that can execute on computers distributed across theInternet

- Visual Basic (based on the original BASIC)- Visual C++ (based on C++)

- Visual C# (based on C++ and Java)

49

1 15 Software Technologies


49/50


1.15 Software Technologies

Agile Software Development

Set of methodologies that try to get software implementedquickly

Agile Alliance (www.agilealliance.org)

Agile Manifesto (www.agilemanifesto.org)

Refactoring

Reworking code to make it clearer and easier to maintain whilepreserving its

Design patterns

Proven architectures for constructing flexible and maintainableobject-oriented software

Open source code

50

1 15 Software Technologies (Cont )


50/50


1.15 Software Technologies (Cont.)

Linux Open source operating system

Apache Most popular open source web server

MySQL Open source database management system

PHP Most popular open source server-side scripting language for developing Internet-based

applications

LAMP Linux, Apache, MySQL and PHP (or Perl or Python)

Game programming Software techniques used in game programming Adobe Flash CS3

Ruby on Rails Combines the scripting language Ruby with the Rails web application framework

Developed by 37Signals

Software as a Service (SaaS) Software runs on servers elsewhere on the Internet

- Salesforce.com, Google, Microsoft and 37Signals all offer SaaS

Documents

Kap 1 Engelsk