Nell Dale & John Lewis

(adaptation by Michael Goldwasser)

The World Wide Web

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The World Wide Web

The Web is an infrastructure of distributed information combined with software that uses networks as a vehicle to exchange that information

A Web page is a document that contains or references various kinds of data, such as text, images, graphics, and programs

Web pages also contain links to other Web pages so that the user can “move around” as desired

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The World Wide Web

A Web site is a collection of related Web pages

The Internet makes the communication possible, but the Web makes that communication easy, more productive, and more enjoyable

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Web Browser

A browser is a software tool that issues the request for the Web page we want and displays it when it arrives

We often talk about “visiting” a Web site, as if we were going there

In truth, we actually specify the information we want, and it is brought to us

The concept of visiting a site is understandable in that we often don’t know what’s at a particular site until we “go to it” and see

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Web Browser

The computer that is set up to respond to Web requests is called a Web server

A Web address is the core part of a Uniform Resource Locator, or URL, which uniquely identifies the page you want out of all of the pages stored anywhere in the world

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Web Browser

Figure 16.2 A browser retrieving a Web page

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HTML

Web pages are created (or built) using a language called the Hypertext Markup Language, or HTML

The term markup language comes from the fact that the primary elements of the language take the form of tags that we insert into a document to annotate the information stored there

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HTML

Figure 16.2
A marked-up document

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HTML

Figure 16.3
The Student Dynamics Web page as displayed in Netscape Navigator

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HTML

Figure 16.4
The HTML document defining the Student Dynamics Web page

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HTML

Tags are enclosed in angle brackets
(<. . . >)

Words such as HEAD, TITLE, and BODY are called elements and specify the type of the tag

Tags are often used in pairs, with a start tag such as <BODY> and a corresponding end tag with a / before the element name, such as </BODY>

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HTML

The browser determines how the page should be displayed based on the tags

Ignores the way we format the HTML document using carriage returns, extra spaces, and blank lines

Takes into account the width and height of the browser window

When you resize the browser window, the contents of the Web page are reformatted to fit the new size

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Basic HTML Formatting

The paragraph tags (<P> . . . </P>) specify text that should be treated as a separate paragraph

The center tags (<CENTER> . . . </CENTER>) indicate that the enclosed information should be centered in the browser window

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Basic HTML Formatting

The B, I, and U elements are used to indicate that the enclosed text should be bold, italic, or underlined, respectively

The <HR> tag inserts a horizontal rule (that is, a line) across the page

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Basic HTML Formatting

We often have cause to display a list of items

The UL element stands for an unordered list, and the LI element represents a list item

Several elements are used to define headings in a document

There are six predefined heading elements defined in HTML: H1, H2, H3, H4, H5, and H6

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Images and Links

Many tags can contain attributes that indicate additional details about the information or how the enclosed information should be displayed

An image can be incorporated into a Web page using the IMG element, which takes an attribute that identifies the image file to display

<IMG SRC = "myPicture.gif">

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Images and Links (cont.)

A link is specified using the element A, which stands for anchor

The tag includes an attribute called HREF that specifies the URL of the destination document.

For example

<A HREF = "http://duke.csc.villanova.edu/docs/">	Documentation Central!</A>

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Interactive Web Pages

When HTML was first developed, there was no way to interact with the information and pictures presented in a Web page

As users have clamored for a more dynamic web, new technologies were developed to accommodate these requests

Some (but not all) of the new ideas were offshoots of the newly developed Java programming language

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Java Applets

A Java applet is a program that is designed to be embedded into an HTML document and transferred over the Web to someone who wants to run the program

An applet is embedded into an HTML document using the APPLET tag

<APPLET code="MyApplet.class" width=250
height=150 ></APPLET>

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Java Applets

Java programs are compiled into Bytecode,
a low-level representation of a program that is not the machine code for any particular type
of CPU

Java applets are restricted as to what they
can do

The Java language has a carefully constructed security model

An applet, for instance, cannot access any local files or change any system settings

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Java Server Pages

A Java Server Page, or JSP, is a Web page that has JSP scriptlets embedded in them

A scriptlet is a small piece of executable code intertwined among regular HTML content

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Java Server Pages

A JSP scriptlet is encased in special tags beginning with <% and ending with %>

Imagine JSP scriptlets as having the expressive power of a full programming language

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Java Server Pages

Note that JSPs are executed on the server side where the Web page resides

By the time it arrives at your computer, all active processing has taken place, producing a static (though dynamically created) Web page

JSPs are particularly good for coordinating the interaction between a Web page and an underlying database

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XML

HTML has a predefined set of tags and each tag has its own meaning

There is nothing about HTML tags that describes the true content of a document

The Extensible Markup Language, or XML, allows the creator of a document to describe its contents by defining his or her own set of tags

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XML

XML is a metalanguage

A metalanguage is a language for talking about, or defining, other languages

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XML

Like HTML, an XML document is made up of tagged data

Figure 16.5 An XLML document containing data about books

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XML

Document Type Definition (DTD): a specification of the organization of the document

The structure of a particular XML document is described by its corresponding DTD document

Figure 16.6 The DTD document corresponding to the XML books document

XML

XML represents a standard format for organizing data without tying it to any particular type of output

Extensible Stylesheet Language (or XSL): A language for defining transformations from XML documents to other output formats

Figure 16.7
An XML document can be transformed into many output formats

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Ethical Issues: Cookies

Internet cookies are very small text files (usually about 50 to 150 bytes) that are downloaded from a Web server to a Web browser

Cookies were intended to allow a server to maintain information about those that visit it

For example, the cookie could contain a user ID and password for a Web site so that the information would not have to be reentered every time the Web site is visited

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Ethical Issues: Cookies

Companies, called targeted marketing companies, have evolved that sell cookie services

These companies pay Web sites to send them copies of the cookies for each transaction and thus build up a profile of a user’s Internet habits

This information is used for marketing and advertising purposes.

Some people like the idea of having marketing and advertising targeted to their interests

Others feel that this is an invasion of privacy

PowerPoint Presentation

Jones & Bartlett Publishers

2002-06-09T13:56:08

Michael Goldwasser