Introduction to Computers and the Internet

2008 Pearson Education, Inc. All rights reserved.

1

11

Introduction to Computers and

the Internet


2

The renaissance of interest in the web that we call Web 2.0 has reached the mainstream.

—Tim O’Reilly

Billions of queries stream across the servers of these Internet services—the aggregate thoughtstream of humankind, online.

—John Battelle, The Search

People are using the web to build things they have not built or written or drawn or communicated anywhere else.

—Tim Berners-Lee

Some people take what we contribute and extend it and contribute it back [to Ruby on Rails]. That's really the basic open source success story.

—David Heinemeier Hansson, interviewed by Chris Karr at www.Chicagoist.com


3

OBJECTIVES

In this chapter you will learn: Basic computing concepts. The different types of programming

languages. The evolution of the Internet and the World

Wide Web. What Web 2.0 is and why it’s having such

an impact among Internet-based and traditional businesses.

What Rich Internet Applications (RIAs) are and the key software technologies used to build RIAs.


4

1.1 Introduction

1.2 What Is a Computer?

1.3 Computer Organization

1.4 Machine Languages, Assembly Languages and High-Level Languages

1.5 History of the Internet and World Wide Web

1.6 World Wide Web Consortium (W3C)

1.7 Web 2.0

1.8 Personal, Distributed and Client/Server Computing

1.9 Hardware Trends

1.10 Key Software Trend: Object Technology

1.11 JavaScript: Object-Based Scripting for the Web

1.12 Browser Portability

1.13 C, C++ and Java

1.14 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

1.1 Introduction Internet 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 www.deitel.com/books/iw3htp4.

– JavaScript, XHTML and CSS- Introduced in earlier chapters

- Provides solid foundation for computer programming and rest of book


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 well as object-

oriented programming

– Allows development of applications with graphical user interfaces (GUIs)

- Multimedia capabilities

- Integration with the Internet and World Wide Web


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 running different 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 2 and 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

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


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

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

Every computer divided into six units1. Input unit

- “Receiving” section of computer- Obtains data from input devices

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

- Places data at disposal of other units

2. 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

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, multiplication and division)

- Contains decision mechanisms and can make comparisons

1.3 Computer Organization (Cont.)


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

1.4 Machine Languages, Assembly Languages and High-Level Languages

Three general types of programming languages– Machine languages

– Assembly languages

– High-level languages


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

+1300042774

+1400593419

+1200274027

– Slow and tedious for most programmers

1.4 Machine Languages, Assembly Languages and High-Level Languages (Cont.)


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:

LOAD BASEPAY

ADD OVERPAY

STORE GROSSPAY



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:

grossPay = basePay + overTimePay



18

High-level languages (II)– Much more desirable from programmer’s 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 programs without 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 Rails—each of these scripting languages is processed by interpreters

– Study markup languages - XHTML and XML, which can be processed by interpreted scripting

languages- Achieve their goal of portability across a variety of platforms



19

Performance Tip 1.1

Interpreters have an advantage over compilers in scripting. An interpreted program can begin executing as soon as it is downloaded to the client’s machine, without the need to be compiled before it can execute. On the downside, scripts generally run much slower than compiled code.


20

Portability Tip 1.1

Interpreted languages are more portable than compiled languages. Interpreters can be implemented for each platform on which the interpreted languages need to execute.


21

Software Engineering Observation 1.1

Interpreted languages are more dynamic than compiled languages. For example, server-side applications can generate code in response to user interactions, and that code can then be interpreted in a browser.


22

1.5 History of the Internet and World Wide Web ARPANET

– Implemented in late 1960’s by ARPA (Advanced Research Projects Agency of DOD)

– Networked computer systems of a dozen universities and institutions with 56KB communications lines

– Grandparent of today’s Internet

– Intended to allow computers to be shared

– Became clear that key benefit was allowing fast communication between researchers – electronic-mail (email)


23

1.5 History of the Internet and World Wide Web ARPA’s 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 dedicated communications lines

– Network designed to be operated without centralized control

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


24

1.5 History of the Internet and World Wide Web Transmission Control Protocol (TCP)

– Name of protocols for communicating over ARPAnet

– Ensured that messages were properly routed and that they arrived intact

Organizations implemented own networks– Used both for intra-organization and communication


25

1.5 History of the Internet and World Wide Web Huge variety of networking hardware and software

appeared– ARPA achieved inter-communication between all platforms

with 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

1.5 History of the Internet and World Wide Web Internet traffic grew

– Businesses spent heavily to improve Internet - Better service their clients

– Fierce competition among communications carriers and hardware and 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 new

information system = World Wide Web- Hypertext Transfer Protocol (HTTP)—a communications protocol used

to 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

1.6 World Wide Web Consortium (W3C) W3C Founded in 1994 by Tim Berners-Lee Homepage at www.w3.org Goals

– Internet universally accessible– Standardization

- W3C Recommendations:

Technologies standardized by W3C

include the Extensible HyperText Markup Language (XHTML), Cascading Style Sheets (CSS), HyperText Markup Language (HTML—now considered a “legacy” technology) and the Extensible Markup Language (XML).

not an actual software product, but a document that specifies a technology’s role, syntax rules and so forth.


28

1.7 Web 2.0

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

The term Web 2.0 was coined by Dale Dougherty of O’Reilly – Web 2.0 definition = companies use the web as a platform to create

collaborative, community-based sites (e.g., social networking sites, blogs, wikis, etc.).

Web 1.0 (1990s and early 2000s) focused on a small number of companies 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 the platforms.


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 from existing applications and websites into own web applications

– Amazon Web Services

– Maps web services with eBay web services


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

1.8 Personal, Distributed and Client/Server Computing

1977 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 may

be used by client computers distributed throughout the network,

– Client/server computing Popular operating systems

– UNIX, Linux, Mac OS X and Microsoft’s Windows


32

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) = Moore’s 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

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 The Key Software Trend: 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: Object Technology (Cont.) Object technology (continued)

– Object-oriented programming - Programmers work in manner similar to how they see the world - 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


Extensive class libraries of reusable software components are available on the Internet. Many of these libraries are free.


37


Some organizations report that the key benefit object-oriented programming gives them is not software that is reusable but, rather, software that is more understandable, better organized and easier to maintain, modify and debug. This can be significant, because perhaps as much as 80 percent of software cost is associated not with the original efforts to develop the software, but with the continued evolution and maintenance of that software throughout its lifetime.


38

1.11 JavaScript: Object-BasedScripting for the Web

JavaScript– Attractive package for advancing level of programming

language education– Object-based language – Supports proper software engineering techniques– Free as part of today’s most popular Web browsers– Powerful scripting language

- Portable- Programs execute interpretively on client machines

– ActionScript and JavaScript are converging in the next version of the JavaScript standard (JavaScript 2/ECMA Script version 4)

- Universal client scripting language, simplifying web application development


39

Good Programming Practice 1.1

Write your programs in a simple and straightforward manner. This is sometimes referred to as KIS (“keep it simple”). One key aspect of keeping it simple is another interpretation of KIS—“keep it small.” Do not “stretch” the language by trying bizarre us es.


40

Portability Tip 1.2

Although it is easier to write portable programs in JavaScript than in many other programming languages, differences among interpreters and browsers make portability difficult to achieve. Simply writing programs in JavaScript does not guarantee portability. Programmers occasionally need to research platform variations and write their code accordingly.


41

Portability Tip 1.3

When writing JavaScript programs, you need to deal directly with cross-browser portability issues. Such issues are hidden by JavaScript libraries (e.g., Dojo, Prototype, Script.aculo.us and ASP.NET Ajax) which provide powerful, ready-to-use capabilities that simplify JavaScript coding by making it cross-browser compatible.


42

Error-Prevention Tip 1.1

Always test your JavaScript programs on all systems and in all web browsers for which they are intended.


43

Good Programming Practice 1.2

Read the documentation for the JavaScript version you are using to access JavaScript’s rich collection of features.


44

Error-Prevention Tip 1.2

Your computer and JavaScript interpreter are good teachers. If you are not sure how a feature works, even after studying the documentation, experiment and see what happens. Study each error or warning message and adjust the code accordingly.


45

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 and

platforms in use

– Find correct mix between absolute portability, complexity and usability of features


46

Portability Tip 1.4

The web is populated with many different browsers, which makes it difficult for authors and web application developers to create universal solutions. The W3C is working toward the goal of a universal client-side platform.


47

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-oriented

programming 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# and .NET

BASIC – Developed in the mid-1960s at Dartmouth College – Primary purpose was to familiarize novices with programming

techniques Microsoft’s Visual Basic language

– Based on Basic– Has become one of the most popular programming languages in the

world Microsoft’s .NET platform

– Provides the capabilities developers need to create computer applications that can execute on computers distributed across the Internet

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


49

1.15 Software Technologies

Agile Software Development – Set of methodologies that try to get software implemented

quickly – Agile Alliance (www.agilealliance.org) – Agile Manifesto (www.agilemanifesto.org)

Refactoring – Reworking code to make it clearer and easier to maintain while

preserving its

Design patterns – Proven architectures for constructing flexible and maintainable

object-oriented software– Open source code


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

Introduction to Computers and the Internet