Chapter 9: Web Programming and Related Tools

1
Chapter 9 Web Programming and Related Tools

• i-Net Guide to the Internet
• Third Edition

2
Objectives

• Investigate tools that you can use in developing
  dynamic Web pages
• Sample several programming languages used to
  build Web sites
• Write simple Web page scripts
• Learn how cookies are used on Web pages

3
Cascading Style Sheets

• Cascading style sheets (CSS), developed by the
  World Wide Web Consortium (W3C), is a feature of
  HTML that makes it possible to apply consistent
  formatting to the HTML documents in a Web site.
• CSS helps Web developers separate the design of a
  Web site from the content included in the Web
  site.
• CSS works by controlling how the information on a
  Web page or entire Web site is displayed.

4
Cascading Style Sheets (Continued)

• An external style sheet is a text file that
  contains rules for controlling how the browser
  displays a Web page that refers to the style
  sheet.

5
XML (Extensible Markup Language) and XSL
(Extensible Style Language)

• HTML is a subset of the Standard Generalized
  Markup Language (SGML), which is a standard for
  several markup languages.
• A markup language has special codes that are
  inserted in a text file to instruct software how
  to display or print the text.
• A newer markup language standard, called XML
  (Extensible Markup Language), is gaining
  popularity.

6
XML (Extensible Markup Language) and XSL
(Extensible Style Language) (Continued)

• XML supports the standards of SGML, while adding
  flexibility and power.
• XML is not concerned about how a Web page looks.
• Instead, XML is used to define and manage data.
• Many applications of XML are emerging, one of
  which is XSL (Extensible Style Language).
• XSL is a style language similar to CSS.

7
XML (Extensible Markup Language) and XSL
(Extensible Style Language) (Continued)

• An XSL file can contain styles, HTML, and
  pointers to XML files, which contain the data and
  tags.
• XML uses a file called a document type
  definitions (DTD) file.
• The DTD file provides a list of the tags,
  attributes, and all entities that can be
  contained in an XML document as well as their
  relationships to each other, and might even
  include how they can be arranged together on the
  page.

8
XHTML (Extensible Hypertext Markup Language)

• Another application that uses XML is XHTML
  (Extensible Hypertext Markup Language), which
  integrates many of the features of XML into HTML.
• Although XHTML tags are nearly identical to those
  in simple HTM, XHTML is stricter.
• Developers must be certain their pages follow all
  the syntax rules of XHTML.

9
XHTML (Extensible Hypertext Markup Language)
(Continued)

• Pages that do follow the XHTML syntax rules are
  said to be well-formed.
• XHTML is case sensitive, which means that all
  tags must be lowercase.
• In XHTML, attributes must always be enclosed in
  quotation marks.

10
Introduction to Programming

• A program is a list of instructions that are
  executed by an operating system or other
  software.
• Sometimes, the program is written into a text
  file called a source file and is then assembled
  into a coded binary format called object code.
• Next, the object code is combined with utilities
  that it needs and is then converted and stored
  into an executable file, so named because it is
  executed by the operating system.

11
Introduction to Programming (Continued)

• Compiling is the process of translating the
  programming code, which a human can understand,
  into binary code, which the computer can
  understand.

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Introduction to Programming (Continued)

• Scripts and macros are two types of programs that
  generally do not need to be compiled.
• These types of programs are sometimes very short,
  containing a list of instructions for performing
  a task, making decisions based on input, and
  producing output.
• Web pages that can change their content are
  called dynamic Web pages or dynamic HTML (DHTML).
• Web pages that do not change their content are
  called static Web pages.

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Two Kinds of Programs

• A program executed on the server is called a
  server-side script or server-side program.
• A script executed on the client computer is
  called a client-side script or client-side
  program.

14
Basic Programming Concepts

• A programming protocol is a set of rules or
  standards by which programs interact with the
  outside world.
• A programming language, on the other hand, is a
  set of words or codes that are used to write a
  program.
• A command is an order to perform an action, such
  as to get a file.
• An argument customizes the action that is stated
  in the command.

15
Basic Programming Concepts (Continued)

• Commands and their arguments are similar to tags
  and their attributes in HTML.

16
Objects

• An object is a small program that performs a
  specific task.
• It is like a middleman who manages the interface
  between the program and some other entity.
• Objects can be written in several different
  programming languages and can run on a variety of
  operating systems.

17
Objects (Continued)

• The CORBA (Common Object Request Broker
  Architecture) standard allows objects to
  communicate with each other regardless of the
  language in which they were written or the
  operating system on which they run.
• To use CORBA, both client and server must be
  running an ORB (Object Request Broker).

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Objects (Continued)

• A dynamic link library (DLL) is a library of
  objects used by other programs to perform a
  specific task or group of related tasks.
• DLLs enable many applications to share the same
  objects easily.
• DLLs ease the process of upgrading or adding bug
  fixes to an operating system.

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Functions

• A function is a segment of programming code that
  can be executed out of order from the main list
  of commands on an as-needed basis.
• Both objects and functions perform a task off to
  the side of the main flow of the program.
• The difference between an object and a function
  is that an object is external to the program and
  can even be written in a different programming
  language, but a function is programming code
  included in the program.

20
Functions (Continued)
21
Survey of Programming Languages Used on the
Internet

• Languages have evolved over the past several
  decades based on changing needs and competition
  among manufacturers.
• Because programming on the Internet has become
  popular, much attention has been given to
  improving programming languages.
• As a result, some languages have already been
  through several versions, with each version
  gaining increased Internet functionality.
• Table 9-1 on page 559 lists the programming
  protocols and languages used on the Web.

22
Programming Protocols

• Keep in mind that a language can use more than
  one protocol and a protocol can be used by
  several languages.
• Analogies include addressing an envelope and
  writing a business letter.
• You use one protocol for addressing envelopes and
  another protocol for writing a business letter.
• Each can be done in several languages (English,
  Spanish, and so forth).

23
CGI (Common Gateway Interface)

• The first, and still a very popular, protocol for
  a program or script for interacting with a Web
  server is CGI (Common Gateway Interface), which
  originally was developed for use on UNIX
  computers.
• When you use CGI, the URL points to a program
  file on the Web server.
• The file is an executable binary file that is
  loaded and executed by the Web server when a
  browser requests that URL.

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CGI (Common Gateway Interface) (Continued)

• The program then builds a Web page that can be
  sent to the browser.

25
ISAPI (Internet Server Application Programming
Interface)

• Another protocol is ISAPI (Internet Server
  Application Programming Interface), which was
  originally developed by Microsoft for use on
  Windows NT servers that were using Microsoft Web
  server software, Internet Information Server
  (IIS).
• The fundamental difference between a CGI program
  and an ISAPI program is the way the Web server
  relates to both.

26
ISAPI (Internet Server Application Programming
Interface) (Continued)

• First, remember that a Web server is an
  executable program.
• With ISAPI, there is a lot of interaction because
  the Web server relates to the ISAPI program as
  its object or DLL.
• Even though they are separate entities, each
  depends on the other for successful execution.

27
Active Server Pages (ASP)

• Active Server Pages (ASP) technology by Microsoft
  is another step in the development of easier and
  more powerful ways to handle server-side
  programming.
• ASP allows you to write a Web page with one or
  more scripts on the page.
• The server executes the ASP script that uses the
  ISAPI method to call DLLs to do some of the work
  of customizing the Web page based on information
  sent from the browser and information about the
  server environment.

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Active Server Pages (ASP) (Continued)

• After the script has finished customizing the
  page, the Web server sends it to the browser.

29
Java Server Pages (JSP)

• Sun Microsystems has developed Java Server Pages
  (JSP), which is a protocol similar to, and a
  competitor of, Microsoft Active Server Pages.
• Java Server Pages can be used to include Java
  programming in HTML on a Web page.
• Java is a programming language developed by Sun
  Microsystems from C.

30
Java Server Pages (JSP) (Continued)

• The short segments of Java commands inserted
  inside the HTML Web page by JSP are called Java
  servlets, which are small Java programs that run
  on the server.
• A JavaBean is a small Java object that works as a
  reusable component in many different situations.

31
SAPI and JSAPI

• Web sites also provide competing technologies for
  speech recognition.
• Microsoft offers Speech Application Programming
  Interface (SAPI) and Sun offers Java Speech API
  (JSAPI).
• In addition, Sun has developed a markup language
  called Java Speech Markup Language (JSML) that
  uses JSAPI.

32
Server-Side Includes (SSI)

• Server-Side Include (SSI) is a simple, one-line
  form of server-side scripting. It has own
  protocols that allow you to use variable values,
  which can be included in the HTML code before it
  is sent to the browser.
• SSI lets you include a line in the HTML file that
  indicates that a variable value needs to be
  entered before the file is sent to the browser.

33
Programming Languages Used by Server and Client

• Many programming languages can use either the CGI
  or ISAPI specifications.
• ASP can be used by only three scripting
  languagesVBScript, PerlScript, and
  JavaScriptand SSI is limited to a few HTML tags.

34
Perl

• Perl (Practical Extraction and Report Language)
  originally was written for shell scripts for the
  UNIX operating system.
• In certain situations, Perl can be used on the
  client.
• Netscape Navigator supports a Perl plug-in that
  allows it to run some Perl scripts and applets
  downloaded from Web sites.

35
C and C

• C is a popular programming language developed in
  1972 by Bell Laboratories and later standardized
  by the American National Standards Institute
  (ANSI).
• The language is compiled, meaning that the file
  containing the original list of commands is input
  into another program to generate a binary
  encrypted file that becomes the executable file.
• This file customarily has an .exe file extension.

36
C and C (Continued)

• C is an updated evolution of C that uses an
  object-oriented approach to programming.
• C is available on most operating system
  platforms, including UNIX, Windows, and
  Macintosh.
• The C language provides many objects and can
  make use of other objects provided by the
  operating system.

37
Java

• Java is another object-oriented language that was
  developed by Sun Microsystems.
• Small Java programs can be downloaded from a Web
  server and executed by a Web browser if the
  browser is capable of interpreting Java code.
• These small Java programs are called Java applets.

38
PHP

• PHP (Hypertext Preprocessor) is a scripting
  language originally developed by the Apache
  Software Foundation for the Apache Web Server on
  a UNIX platform, although it has been ported to
  other Web servers and operating systems.
• It can relate to a Web server using the CGI
  protocol, is easy to learn and use, and is free.

39
Visual Basic

• Visual Basic (VB), by Microsoft, is a very
  popular language because it is relatively easy to
  learn and, because it is written by Microsoft,
  interacts well with Windows operating systems.
• Just like C and C, Visual Basic is a compiled
  language - the program is an executable binary
  file.
• Visual Basic can use DLLs effectively and is an
  object-oriented language.

40
VBScript, PerlScript, JavaScript, and JScript

• VBScript is a subset of Visual Basic for
  Applications, which is a subset of Visual Basic.
• VBScript is the default scripting language of
  ASP.
• PerlScript is an off-shoot of and is similar to
  Perl - it uses some of the same code and
  functions.
• JavaScript, developed by Netscape for use with
  Netscape Navigator, resembles Java, but is not a
  subset of Java in the way that VBScript is a
  subset of Visual Basic.

41
VBScript, PerlScript, JavaScript, and Jscript
(Continued)

• JavaScript is interpreted by most browsers and is
  the scripting language of choice if you want to
  serve the most Internet users.
• To compete with JavaScript, Microsoft developed a
  similar scripting language called Jscript, but
  there are slight inconsistencies between the
  scripting languages and the way Netscape
  Navigator and Internet Explorer interpret each.
• The new hybrid version of the scripting language
  is called ECMAScript.

42
Learning to Use Scripts

• All you need to execute a client-side script is a
  browser therefore, a beginner can easily
  practice client-side scripting.
• Learning to use server-side scripts requires a
  Web server to interpret the script.
• For an SSI or ASP script, you must type the
  script into the Web page, publish the Web page to
  the server, and then use your browser to access
  the page.

43
Learning to Use Scripts (Continued)

• When you want to insert scripts on a Web page,
  you must include tags to mark the beginning and
  end of the script.

44
Learning to Use Scripts (Continued)
45
Including the Date on a Web Page

• In the JavaScript example listed on page 570 and
  shown in Figure 9-22, the script retrieves and
  displays the system date.

46
Adding a Button to a Web Page

• The next example introduces HTML commands that
  add a button to the Web page.
• When a user clicks the button, a message appears
  in a box.
• JavaScript commands are used to create the box
  and its message.
• The program uses the onClick command, which calls
  a specific function when the button is clicked.

47
Adding a Button to a Web Page (Continued)
48
Creating a Script that Checks for Errors in User
Input

• In the example on page 574 of client-side
  scripting, you see how a script can validate data
  before the data is sent to the server for
  processing.
• Make sure to validate data so bad data is not
  accepted when a user clicks the Send button.
• This Web page displays a message to the user and
  invites the user to enter her name and e-mail
  address, and then click the Send button to send
  the data to the server.

49
Creating a Script that Checks for Errors in User
Input (Continued)

• The client-side script verifies that the e-mail
  address contains the _at_ symbol.
• When the user enters correct data in the form on
  the errorchk.htm Web page, the form on the page
  sends the data to another Web page on the server.

50
Server-Side Scripting

• One important job that can be performed by
  server-side scripts is maintaining a conversation
  between a Web browser and a Web server.
• A Web server keeps no records of previous
  requests from a Web browser or replies to those
  request.

51
Server-Side Scripting (Continued)

• A dialog between the browser and server-side
  scripts might go something like this
• The Web server gives a Web page of items offered
  for sale to the browser.
• The user selects items from a form on the Web
  page.
• The server receives the URL and formats the Web
  page showing the selected items with a form that
  allows the user to select a shipping method.

52
All About Cookies

• Cookies are used to
• Personalize a Web site with the users name or
  other information.
• Remember what a person has purchased or placed in
  a shopping cart to purchase later.
• Track Web site activity to see who has visited
  the site and which pages on the site they access.
• Target marketing efforts based on your interests.

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Using Cookies

• A cookie is a shortcut method of tracking
  information about the user without having to
  prompt the user each time the information is
  needed.
• A cookie can contain coded information that only
  the server that created it can understand.
• If a cookie is marked as a secure cookie, it is
  only transmitted to the server when a session is
  secured.

54
Using Cookies (Continued)

• Some people are concerned about privacy and dont
  want cookies stored on a computer.
• This can be a valid concern when the computer is
  not your own personal computer, such as one at
  work, in a public library, or other public
  location.

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How Cookies Work

• A cookie is created when the HTTP header contains
  the command Set-Cookie.
• Information about the cookie is included in the
  header and a name/value pair contains the data.
• Later, when the user again requests Web pages
  from the Web site that created the cookie, the
  browser recognizes that it is holding a cookie
  for this Web site and sends the cookie
  information in the HTTP header when requesting
  the page.

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How Cookies Work (Continued)
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Summary

• CSS is used by developers for creating a group of
  Web pages that have consistent formatting
  throughout the entire Web site.
• Scripts are used on either the server
  (server-side script) or the client (client-side
  script) to customize a Web page.
• Similar to Active Server Pages, Java Server Pages
  (JSP) is a technology that allows Java
  programming segments to be written into a Web
  page and executed by the server before the page
  is downloaded to the browser.

58
Summary (Continued)

• One of the first languages to use CGI was Perl,
  which first was used as a UNIX shell scripting
  language by UNIX system administrators.
• VBScript is a subset of Visual Basic, Jscript is
  the Microsoft look-alike language for Netscapes
  JavaScript.
• JavaScript resembles Java but is not a subset of
  Java.