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Web 101 Third Edition by Wendy G. Lehnert & Richard L. Kopec. Chapter 11: Web Pages and Scripting Alternatives. Learning Objectives. Learn what CGI means Find out what Java applets can do and how to add them to your Web pages.

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web 101 third edition by wendy g lehnert richard l kopec
Web 101

Third Edition

by Wendy G. Lehnert & Richard L. Kopec

Chapter 11:Web Pages and Scripting Alternatives

learning objectives
Learning Objectives
  • Learn what CGI means
  • Find out what Java applets can do and how to add them to your Web pages.
  • Learn how data-driven Java applets make it easier to manage frequent Web page updates.
  • Learn about XML
  • Learn about AJAX and how it works
  • Learn about PHP
taking charge
Taking Charge
  • It’s very easy to add dynamic elements to your Web pages.
  • Ready-made JavaScripts and Java applets are available on the web for you to add to your Web page.
  • A JavaScript is a bit of code written to enhance a Web page.
  • A Java Applet is a small Java program that is attached to a web page.
taking charge1
Taking Charge
  • A Script is a small computer program written in a scripting language.
  • Scripts can be customized for you at an interactive Web site established for this purpose. (http://www.htmlgear.lycos.com/)
  • You can also download an authoring tool that helps you to do the same thing. (http://www.htmlgoodies.com/)
  • You can visit a freeware site and cut and paste one into your Web page.
taking charge2
Taking Charge
  • Some Javascript freeware sites (from Chapter 10):http://www.wsabstract.com/

http://Javascript.internet.com/

http://www.JavaScriptsearch.com/

taking charge3
Taking Charge
  • A scripting language is usually more limited and simpler than a full-fledged programming language.
  • Javascript interpreters are built-in to your Web browser, so no additional server support is needed to use it.
  • In addition to Javascript, your Web server might also support PHP or Perl.
  • PHP is a more standardized and potentially easier to use scripting language than Javascript.
  • Perl is another common scripting language.
  • There are also applets, small programs written in Java that can also be used on Web pages.
cgi scripts
CGI Scripts
  • Some Web programs are intended to be done on the client computer, but others work best when done by the server.
  • In order to use server-side programs, the client must pass information to the server.
  • The protocol used by the client to pass needed information to the server is known as a Common Gateway interface (CGI).
  • The programs that process this information are known as CGI scripts.
  • Web page hit counters are commonly implemented this way:
cgi scripts1
CGI Scripts
  • A hit counter MUST be implemented on a server - Javascript cannot write to storage for security reasons - a rogue Javascript program could do a great deal of damage!
  • The hit count data collected by your computer is sent to a server for storage by the hit counter CGI Script whenever your Web page is accessed.
  • These CGI services are often housed on a 3rd-party computer, so three computers are involved: 1) one hosts the Web browser requesting the page, 2) one stores and serves the Web page, and 3) one offers the CGI service and data storage.
cgi scripts2
CGI Scripts
  • To install your own CGI scripts, you need access to a Web server that supports CGI.
  • Because of security concerns, such access is often very limited, if available at all.
  • CGI scripts are often written by programmers for programmers, but there are some that you can try.
  • Live Counter: http://www.chami.com/counter/classic/
  • There are 5 files:

1. a “.class” file (a Java applet)

2. Three “.pl” files (a CGI Perl script)

3. A “.gif” file (images of the counter digits)

cgi scripts3
CGI Scripts
  • If your Web server supports CGI, you might consider trying LiveCounter.
  • Besides hit counters, CGI scipts can be used to
    • password protect your Web page
    • store data
    • add a site specific search engine to a web site
java applets
Java Applets
  • An applet is a small executable program written in Java attached to a Web page.
  • Applets require that a JVM be installed on the client computer.
  • A JVM (Java Virtual Machine) is a platform-specific browser add-on that makes it possible for Web browsers to execute Java applets.
java applets1
Java Applets
  • Java is a full-fledged programming language.
  • Applets pose less of a risk than scripts do.
  • Applets can’t carry viruses since they can’t write to the local machine.
java applets2
Java Applets
  • Programming Java Applets will require programming skill
  • You can find freely available applets online at applet sites
  • As an applet is software, so it will have a license too
java applets3
Java Applets
  • To install an applet:
    • Download and unpack the applet
    • Read all available documentation
    • Insert the required HTML snippet into your Web page
    • Modify the PARAM values as needed
    • Upload your Web page to the server
    • Upload the required .class file
    • Upload any required support files
data driven web pages
Data-Driven Web Pages
  • Data-driven Web page displays are used to minimize the amount of effort needed for ongoing Web page maintenance.
  • A Java applet reads and displays the information contained in a text data file.
  • Only that text file needs to be updated.
  • These applets are often highly customizable
data driven web pages2
Data-Driven Web Pages
  • Data-driven displays are not limited to text.
  • They can accept data from the user.
  • Applets that do this are freely available on the Web.
slide18
XML
  • Data-driven Web (DDW) sites do not work well with HTML because DDW pages are based on separation of content from presentation.
  • eXtensible Markup Language (XML) is a markup language designed to organize content (the data).
  • XML works cooperatively with CSS to present this content.
  • XML is often called a data description language.
slide19
XML
  • XML allows the user to define application-specific tags.
  • The user can use these tags to describe how the elements should be arranged relative to each other.
  • A CSS file can be created that describes how to display each of the user-defined elements.
  • An XML-enabled browser could then be used to display the Web page described.
slide20
XML
  • A sample XML content description:

<!DOCTYPE news-list [

<!ELEMENT news-list (title, news*)>

<!ELEMENT news (header, body, link?)>

<!ELEMENT title ANY>

<!ELEMENT header ANY>

<!ELEMENT body ANY>

<!ELEMENT link ANY>

]>

slide21
XML
  • A sample XML data file:

<news-list>

<title>Announcements</title>

<news>

<header>Assignment #4 Due Date Extension</header>

<body>The deadline for assignment #4 has been extended to 6pm on Friday, April 5.</body>

</news>

<news>…</news> // another news element

<news>

<header>Course Project Assignments for 120</header>

<body>These are the course projects for the 9:30 folks.</body>

<link>http://www-unix.oit.umass.edu/~lehnert/ assignments.html</link>

</news>

<news>…</news> // another news element

</news-list>

slide22
XML
  • An associated CSS file:

title { font-size: 12pt; font-family: arial;

color: red; font-weight: bold;

text-align: center; margin-top: 10;

margin-bottom: 10; display: block}

header { font-size: 8pt; font-family: arial;

font-weight: bold; margin-top: 10;

margin-left: 6; display: block}

body { font-size: 8pt; font-family: arial;

margin-left: 6; display: block}

slide23
XML
  • The final Web page
slide24
XML
  • XHTML - eXtensible Hypertext Markup Language)
  • Combines HTML and XML.
  • Adds XMLs capability of creating new elements.
  • Most browsers recognize XHTML.
  • A transitional language as the Web pages are transformed from HTML to XML.
slide25
AJAX
  • Asychronous Javascript and XML.
  • Used to implement Web 2.0 applications (Chapter 4).
  • Formerly known as DHTML (dynamic HTML).
  • Allows browser to carry on additional tasks while it waits for some Javascript action to be completed.
  • Normally, browsers “freeze” until the Javascript task is completed.
  • Permits the creation of shared documents like those found in Google Spreadsheets and Docs.
  • Users can be entering data into a spreadsheet while the Javascript engine is busily dispatching it to the server for distribution to other document collaborators.
slide26
AJAX
  • Can also send form data to server as it’s entered, eliminating the need for a Submit button.
  • Used to power:
    • Microsoft Outlook Access
    • Google Maps
    • Yahoo! Maps
    • Flickr
    • Netflix
    • Google Docs
slide27
PHP
  • Newest kid on the scripting block.
  • PHP: Personal home page Hypertext Preprocessor
  • Open Source, server-side, scripting language
  • Intended to produce dynamic Web content.
  • Useful for frequently changing data displayed in stable format.
  • Simplifies task of accessing a database with frequently updated data, extracting desired information, and generating a Web page to display it.
slide28
PHP
  • Server used must support PHP.
    • How to tell?Insert this code into an HTML file:<?phpecho “Your server supports PHP”?>
    • If you see the string appearing in the echo statement above on the web page containing this code, then your server supports PHP.
slide29
PHP
  • PHP can be used to capture data from a Web page, process it, then generate a Web page to display the result.
  • Example, Punky’s Pizza Parlor
  • A “normal” Web page is created to capture order information:
slide30
PHP
  • The HTML file uses the ACTION attribute of the FORM element to trigger the PHP code:<form action=“order.php” method=“post”>
  • As you can probably guess, the PHP code to be executed when the SUBMIT button is pressed can be found in the file “order.php”
  • As you can also probably guess, the extension “.php” is used for files that contain PHP code.
slide31
PHP

/* Start of PHP code */ $pizza = $_POST[‘pizza’]; /* get the pizza type from POST data */ $topping1 = $_POST[‘topping1’]; /* get 1st topping from POST data */ $topping2 = $_POST[‘topping2’]; /* get 2nd topping from POST data */ $topping3 = $_POST[‘topping3’]; /* get 3rd topping from POST data */ $quantity = $_POST[‘quantity’]; /* get quantity ordered from POST data */ /* create HTML page HEAD element */ echo “<html> <head> <title>Pizza Order</title> </head> ”; /* start the BODY element */ echo “<body> <h1>Punky’s Pizza Parlor</h1> <h2>Order Confirmation</h2>”; /* Report the order data */ echo “You ordered a ”. $pizza . “ pizza with ” . $topping1 . “, ”. $topping2 . “, and ” . $topping3 . “.<br>”; echo “Number ordered: ” . $quantity . “ <br><br>”; /* compute and report the cost */ printf(“Your cost, including 8%% tax: $%.2f<br>” , ($quantity*10)*1.08); /* write the date and time of order */ echo “Time ordered: ” .date(‘D, d M Y g:i:s A’) . “ <br>”; /* finish the page */ echo “Thank you for ordering from Punky’s Pizza Parlor!”; echo “</body></html>”; /* end of PHP code */

slide32
PHP
  • These assignment statements capture the data entered in the Web page form control elements (the selection lists).
  • As you can see, variables in PHP are preceded by a $ sign.
  • All PHP statements end with a semicolon.

$pizza = $_POST[‘pizza’]; $topping1 = $_POST[‘topping1’]; $topping2 = $_POST[‘topping2’]; $topping3 = $_POST[‘topping3’]; $quantity = $_POST[‘quantity’];

slide33
PHP
  • These echo statements begin building the Web page dynamically, writing it to the browser piece by piece.
  • In PHP concatenation is indicated by a period (Javascript uses a +).
  • Strings are indicated the same way - using single or double quote characters as delimiters.echo “<html> <head> <title>Pizza Order</title> </head> ”; echo “<body> <h1>Punky’s Pizza Parlor</h1> <h2>Order Confirmation</h2>”; echo “You ordered a ”. $pizza . “ pizza with ” . $topping1 . “, ”. $topping2 . “, and ” . $topping3 . “.<br>”; echo “Number ordered: ” . $quantity . “ <br><br>”;
slide34
PHP
  • This statement performs the computation, then prints and formats the results so they look good.
  • The printf statement uses format specifiers: %% (to allow printing of a single %) and %.2f (indicating that a floating point value should be displayed to exactly 2 decimal places)

printf(“Your cost, including 8%% tax: $%.2f<br>” , ($quantity*10)*1.08);

slide35
PHP
  • The echo statement uses the date function to print the current date according to its own specific format specifiers (see next slide).
  • The date format specifier used here isD, d M Y g:i:s A

produces

Sat, 09 Sep 2006 11:23:03 AM

echo “Time ordered: ” .date(‘D, d M Y g:i:s A’) . “ <br>”;

slide36
PHP
  • The date function format specifiers
slide37
PHP
  • These two statements complete the Web page:

echo “Thank you for ordering from Punky’s Pizza Parlor!”;

echo “</body></html>”;

slide38
PHP
  • The Web page produced:
how far can you go without programming
How Far Can You Go Without Programming?
  • Quite a ways!
  • You should be able to build functional and attractive Web pages.
  • Numerous scripts and applets are freely available on the Web to enhance your pages.
  • Many are easily incorporated into your Web page.
  • But some may simply not work!
how far can you go without programming1
How Far Can You Go Without Programming?
  • You can acquire an Integrated Development Environment (IDE) with a Rapid Development Application (RAD) editor which provides Graphical User Interface (GUI) to assist you.
  • You can also hire a programmer to (try rentacoder.com)!
  • Although programming is becoming easier and easier, some coding tasks can be quite challenging even for experienced programmers.
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