Tài liệu Internet Development doc

Chapter

8

Internet Development

i-NET+ EXAM OBJECTIVES COVERED IN THIS
CHAPTER:


Define programming-related terms as they relate to Internet
applications development. Content could include the following:


API


CGI


SQL


SAPI


DLL—dynamic linking and static linking


Client- and server-side scripting



Describe the differences between popular client-side and
server-side programming languages. Examples could include
the following:


Java


JavaScript


Perl


C


C++


Visual Basic


VBScript


JScript


XML


VRML


ASP


Content could include the following:


When to use the languages


When they are executed


Describe the differences between a relational database and a
non-relational database.
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

Identify when to integrate a database with a Web site and the technologies used to
connect the two.


Demonstrate the ability to create HTML pages. Content could include the following:


HTML document structure


Coding simple tables, headings, forms


Compatibility between different browsers


Difference between text editors and GUI editors


Importance of creating cross-browser coding in your HTML


Identify popular multimedia extensions or plug-ins. Examples could include the
following:


QTVR (QuickTime VR)


Flash


Shockwave


RealPlayer



Windows Media Player


Describe the uses and benefits of various multimedia file formats. Examples could include
the following:


GIF


GIF89a


JPEG


PNG


PDF


RTF


TIFF


PostScript


EPS


BMP


MOV


MPEG


AVI


BinHex


Streaming media


Non-streaming media
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T

he state of the art in Internet software development is a slip-

pery thing. New technologies are always emerging; others fade away as
they’re recognized as too weak, too complicated, or too expensive. Your job
as an Internet professional is to stay familiar, in a broad way, with what’s
new in software development. Then, when you’re called upon to solve a par-
ticular problem, you should be able to consult books and Internet resources
to figure out which technologies apply and how to use them. There are no
authorities, only people willing to teach themselves quickly.
This chapter endeavors to introduce you to some Internet software and
media development concepts that seem built to last, at least for a while.
Understanding these will help you grasp the new developments as they
appear.

Network Software Concepts

S

un Microsystems notes in its advertisements that “the network is the
computer.” Increasingly, computation has more to do with sharing informa-
tion among machines than with processing it on any given machine. Clients
request data from servers; servers make requests of other servers; processing
jobs are shared among many machines and therefore accomplished faster.
This section has to do with the design of software systems that are meant to
operate in networked environments.
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Client-Server Architecture

Client-server architecture

describes a particular kind of relationship between
two computers. It’s easy to assume that a server is a big, powerful computer
and that a client is an everyday personal computer, but that’s not necessarily
true. The server in a client-server relationship is simply a computer on which
a particular resource—particular data—resides. The client is a computer that
requests a copy of that information for its own use.
Clients and servers don’t have to be thought of as items of hardware. They
can be separate pieces of software, and indeed the two pieces of software in
the equation can be running under the same processor. You can install a Web
server—Apache, Personal Web Server, whatever—on your machine and
request Web pages from it, using a Web browser that’s running as a separate
process. For this reason, you’ll hear Web browsers referred to as “Web cli-
ents,” just as programs like Apache are called “Web servers,” independent of
the hardware they run on.
When you surf the Web, you’re acting as the client in a series of client-
server relationships. The computers that are identified by domain names—
yahoo.com, amazon.com, and so on—contain collections of data. When you
request a document that’s identified by a particular URL, a copy of that doc-
ument is sent from the computer on which it resides (the server) to your com-
puter (the client). Similarly, when you use your computer to send a query to
a database server and receive a particular set of data in response, your
machine is the client in a client-server relationship. Client-server transactions
need not involve Web pages by any means. However, Web servers and Web
clients illustrate many client-server concepts clearly, so we’ll focus on them

for the present.

Client Software

In the case of Web surfing, a Web browser is the client software in a client-
server relationship. People use their Web browsers to request information
from other computers. The browsers then receive the requested information
and are responsible for presenting it to their users properly. The process of
interpreting and presenting information is not trivial because Web pages can
consist of several different kinds of data:


Text with embedded markup information


Special, embedded content that browsers can interpret without out-
side help
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Network Software Concepts

341


Code written in a scripting language, which must be interpreted and
executed


Code written in Java or an ActiveX language


Content that must be interpreted by a plug-in
Let’s explore these different kinds of content in greater detail.

Text and Markup Languages

The simplest Web pages are just text documents—sequences of characters,
formatted as American Standard Code for Information Interchange
(ASCII)—with special sequences of characters inserted here and there to indi-
cate what the text means and how it should be displayed. You’re probably
somewhat familiar with the most popular Web markup language—it’s called
Hypertext Markup Language (HTML)—and we’ll cover some of its details
later in this chapter. For now, just know that every Web browser incorporates
an HTML interpreter that interprets the HTML tags in documents.
There are other markup languages; eXtensible Markup Language (XML)
isn’t as concerned with how text is displayed as with the meaning of individ-
ual passages of text. XML is one way to share database information among
machines.

Native Embedded Content

In addition to their ability to interpret and display HTML-formatted text,
Web browsers can display certain other kinds of data that is referred to in
HTML documents. Graphics fall into this category. All Web browsers can
interpret JPEG and GIF graphics; various browsers can interpret other image
formats as well (Microsoft Internet Explorer, for example, can display BMP
images). The pieces of software that interpret these embedded files—the

interpreters—

are inseparable parts of the Web browsers.

Scripting Languages

Sometimes, the markup tags that define Web documents include passages of
code in scripting languages like JavaScript or VBScript. You can use scripting
languages to provide your Web pages with a certain level of interactivity and
animation. The code that makes up programs—you’ll learn more about it
later in this chapter—is never compiled. It always remains readable to
human beings. Web browsers that are capable of running scripting-language
programs interpret the code directly, without it first being compiled.
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Java and ActiveX Content
Though they’re kind of like graphics in the sense that they’re assigned a rect-
angular region and interpreted separately from the HTML document in
which they’re embedded, Java applets and ActiveX controls deserve special
mention. Java applets and ActiveX Controls are little pieces of software that
occupy portions of the browser windows in which they run.
Plug-In Content
Although browsers can make sense of and display certain kinds of content
natively, other kinds of files—such as those containing certain kinds of
sounds, three-dimensional graphics, and other special media—fall outside
the browser’s built-in capabilities. The most popular browsers, however, can
take plug-ins, which are software modules that users add to their browsers
to expand their capabilities. When a browser encounters a piece of embed-
ded media that it can’t interpret natively, it checks its roster of plug-ins to see

if one of them can handle the content. If so, the handling is seamless—it
looks to the user as if the browser can handle the content by itself.
The problem with plug-ins is that no one has all of them, and you’re asking a
lot of a user if you ask her to download and install a particular plug-in just to
view your content. The basic rule is to stick to media that browsers can inter-
pret natively. If you need to use plug-in content to get an effect you need—
chemists, for example, use special file formats to display images of complex
molecules in three dimensions—make sure the benefits to users are great
enough to warrant the trouble of downloading and installing the plug-in.
Server Software
In the client-server equation as it applies to Web publishing, the Web server
is both a piece of software (the program that doles out pages in response to
client requests) and a unit of hardware (the physical machine on which the
server software runs).
Popular Web server software includes:

Apache

Microsoft Internet Information Server (IIS)

Netscape Enterprise Server
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Network Software Concepts 343
Each handles requests for Web pages. They may also have capacities to
work with server-side scripting languages, extensions, Java servlets, and inde-
pendent server-side programs that provide some sort of processing service.
Server Extensions
A server extension is sort of like a plug-in for Web server software. A soft-
ware module that expands the capabilities of the server software itself, server
extension may be published by the same company that put out the server

software or by another publisher. The Microsoft FrontPage Extensions are
perhaps the most popular server extensions around. They allow servers to
support some of the interactive features Microsoft FrontPage lets developers
embed in their pages.
Java Servlets
Java servlets are special Java programs that expand the capabilities of Web
server software. Similar to server extensions, the advantage of a Java servlet
is that a single, properly designed servlet will run under any operating sys-
tem for which there is a Java Virtual Machine (JVM)—the same as any Java
program.
Server-Side Scripting Languages
Server-side scripting languages are programming languages designed for
writing code that’s embedded in Web pages and interpreted before those
pages are sent out to the client. Active Server Pages (ASP) and Hypertext Pre-
processor (PHP), both covered later in this chapter, are two of the most pop-
ular server-side scripting languages.
Compiled Server-Side Programs and Other Servers
In addition to exercising their native capabilities and those provided by add-
in servlets and extensions, Web servers may also cooperate with other kinds
of server software, such as a database server. When a program written in a
server-side scripting language requests data from a database server, the Web
server is capable of allowing the script to access the database server and
retrieve the information it needs.
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Communication between Client and Server
If you’re going to have software that takes advantage of client-server archi-
tecture, you must have mechanisms in place for transmitting information

back and forth between the two elements in the equation.
Forms
As far as the Web is concerned, client-server communications rely upon
forms in Web pages that collect information from the user. The data the user
puts into those forms is then submitted (or posted) to the program on the
server side. The form data is packaged and sent to the server in a format
defined by the Common Gateway Interface (CGI) specification.
Common Gateway Interface (CGI)
The Common Gateway Interface (CGI) specification defines a way of pack-
aging text data (such as the contents of a form) for transmission over a net-
work. The CGI specification takes the contents of a form and the names of
the form elements (as specified in HTML) and assembles them all into a
long string of characters. That string can then be passed to a program on
the server side for processing and a response. A CGI submission might tell
a server-side database interface to search for something and return a results
page, for example. Computers running Microsoft’s Internet Information
Server (IIS) support the Internet Services Application Programming Inter-
face (ISAPI), which can be used to carry out CGI-like tasks on IIS-equipped
servers.
Do not make the mistake of thinking CGI is a programming language. It is not.
Although it is correct to speak of a “CGI program,” such programs are referred
to that way because they accept CGI data as input (as from a Web form), not
because they are written in a language called CGI. There is no such language
(at least, there is none of any significance).
Security
The problem with CGI is that it involves the transmission of a text string—
that is by default readable to anybody who cares to intercept it—across a
network. If you’re using CGI to move data over the Internet, you’re exposing
yourself and your client-side users to security risks. You shouldn’t ever enter
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Network Software Concepts 345
sensitive information such as credit card data into a form for CGI transmis-
sion unless you’re sure the transmission will be protected.
How are CGI submissions protected? Typically, Secure Sockets Layer
(SSL) encrypts data transmitted between a client and a server. Read all about
SSL and other encryption technologies in Chapter 7.
Trends in Network Computing
For many years, the trend in computing technology was toward more stor-
age space, faster processors, more capable software, and lower prices on
everything. Now it seems that, although “more, faster, and cheaper” will
always be appealing, computer technology is getting to be “good enough”
for many everyday applications. Personal computers spend most of their
processor cycles idling, waiting for their human users to do something.
The trends in computer technology have mainly to do with network
computing, which is computing performed by multiple computers linked
together on some kind of network. Whether the collaborative computing has
to do with sharing information or sharing processor power, it seems that
a network often provides more computing power than its component
machines could if they were acting alone. You can distinguish the two main
trends in networking by determining what is shared:

In enterprise computing, it’s typically the data that’s shared. One
machine can access and operate upon information from another or
from a central repository.

In distributed computing, the processing work is spread over several
machines.
Of course, there’s some overlap, and it’s not always easy to tell where pro-
cessing begins and data-sharing ends. Let’s explore these trends further.
Enterprise Computing

Enterprise computing has to do with sharing information among the appli-
cations with which an organization, such as a company or a unit of gov-
ernment, does its business. This kind of sharing can help the company
realize efficiencies in its overall process of buying, making, processing, and
selling goods and services and in the accounting, finance, human resources,
and management infrastructures it maintains to facilitate those processes.
An Enterprise Resource Planning (ERP) system, because of its purchasing
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features, might note that two different plants were buying the same part
from different suppliers. Because of its integration with the manufacturing
process, it might note that one supplier’s products had far fewer defects
than the other’s did. The two purchasing agents at the plants might have
had spotty communication without the ERP system, but the ERP system is
much better able to spot situations like this and advise the buyer of the
faulty parts to try the other plant’s supplier.
SAP (pronounced as three distinct letters), a German company, is gener-
ally recognized as the world leader in enterprise computing. Its flagship ERP
product, SAP R/3, is standard equipment among very large organizations all
over the world, and SAP consultants make very good coin planning, imple-
menting, and expanding SAP R/3 installations. The trend is beginning to
trickle down to smaller companies, as well, and some pundits expect that
technologies like XML will make it easier to share information among small-
business software products from many publishers.
SAP has several Web sites, each of which highlights some aspect of its busi-
ness. The main one, www.sap.com, will direct you to the information you need.
Another site, www.mysap.com, focuses on SAP’s products and services for
companies somewhat smaller than enormous.

Distributed Computing
Distributed computing has to do with spreading portions of a computing job
over several machines. This is not parallel processing, in which an operating
system divides the running of some program over several CPUs, but rather
a system of sharing discrete business tasks over several machines. The dis-
crete tasks might include the following:

Collecting data

Managing a database that stores the data

Analyzing the data

Performing financial operations (such as billing) based on the data
Any given task might require work from several machines, each of
which is responsible for one of the above. The load is spread, and therefore
the job is completed more quickly.
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Understanding Programming Languages 347
JavaBeans
JavaBeans are the epitome of componentization in the Java language. It’s
possible to build a Bean with an elaborate feature set and considerable
power, then use it as a sort of “black box” that carries out some particular
duty in various software systems of which it is a part. You can distribute
your Beans to others as well, either freely or, because Beans are compiled and
have no visible source code, commercially. Beans have found application in
Sun’s own graphical user interface toolkit, as well as in other projects.
Component Object Model (COM)
The Component Object Model (COM) is Microsoft’s answer to JavaBeans.
It’s a means of writing independent code modules and having them commu-

nicate with one another. The idea is that you could have a single, specialized
COM module that various other pieces of software (other COM modules and
non-COM programs) refer to for different reasons.
A single COM module might, for example, serve to perform queries on any
specified database. One program might refer to that COM module to query an
employee database; another COM module might refer to the query module for
accessing a sales database. It’s an economy of scale: one COM module does
double duty.
Distributed Component Object Model (DCOM)
Distributed Component Object Model (DCOM) components are really no
different from COM components. DCOM is a subset of COM that includes
COM modules running on different machines and referring to one another
across a network.
Understanding Programming Languages
A
programming language is any system of syntax and grammar that,
when used to generate sets of instructions called programs, can have an effect
on the behavior of a computer. Programming languages broadly include
everything from HTML to C++. Here, we’ll focus on highly capable, full-
featured development languages and slightly less capable (but simpler)
scripting languages.
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Full-Featured Development Languages
A full-featured development language is one that can be used to write stand-
alone programs. You can use a full-featured development language to write
an elaborate word processor, a Web browser, or a database front end. You
could write a whole operating system with certain languages if you wanted

to. Examples of such languages in the network software milieu include:

Java

Visual Basic

C and C++
These are compiled languages. When you have written source code, you
must run it through a special processor called a compiler that translates the
human-readable source code into machine code that processors and operat-
ing systems can understand. An operating system makes its resources avail-
able to programs running under it by means of an application programming
interface (API).
Java fans will tell you that their language is not really compiled, and that’s
sort of true. When you write Java code, you must run it through a program
that converts it to bytecodes, which are instructions that have meaning to an
imaginary chip called the Java Virtual Machine (JVM).
Java
The prime attraction of Java is platform neutrality—a concept that requires
some background. Other programming languages, such as C++, require that
programmers write different programs for different operating environments.
There’s one version of Microsoft Word for Windows 95, another version for
Windows 3.x, and another version for MacOS. That’s not acceptable on the
Internet, where a server might have to provide the same program to many
different kinds of computers—and might not be able to determine what kind
of computer needed the program at a given time. Plus, it’s a pain—an expen-
sive pain—for software developers, who must multiply the effort required to
write a program by the number of platforms they want to support.
The single biggest attraction of Java is that, theoretically, you can write
one Java program, compile it, and expect it to run similarly under Win-

dows 95, MacOS, Solaris, and half a dozen other operating environ-
ments—a feature called architecture neutrality. In practice, architecture
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Understanding Programming Languages 349
neutrality doesn’t work as well as many programmers would like, espe-
cially with complicated graphical programs. But it works fine with simple
programs, and future versions of Java will surely have even better archi-
tecture neutrality. And, most important, other languages don’t even make
attempts at architecture neutrality.
Visual Basic
Microsoft Corporation designed Visual Basic as a tool for fast development
of programs for its Windows operating systems. The latest versions of Visual
Basic incorporate a certain amount of sensitivity to network software devel-
opment, but the primary use of Visual Basic is in writing software for use
under Microsoft Windows 98 and Windows NT. A large portion of the work
done with Visual Basic involves the creation of user interfaces for databases.
Lately, Visual Basic has become more oriented toward network pro-
gramming. You can use Visual Basic to create ActiveX controls for embed-
ding in Web pages that will be interpreted by Microsoft Internet Explorer.
You also can use Visual Basic to create Component Object Model (COM)
components.
You’ll find the latest Microsoft news about Visual Basic at msdn.microsoft
.com/vbasic/.
C and C++
Widely regarded as the top of the heap as far as general-purpose program-
ming languages are concerned, C and C++ are the standards by which most
other such languages are measured. You can do anything with C and C++,
from manipulating the pixels on a video screen individually to reading the
contents of memory one bit at a time. Programs written in the C languages
are fast, too.

What’s the difference between C and C++? The latter is object oriented,
which means (to cite one important characteristic) it supports the creation of
code modules that can inherit traits from other such modules. Say you’d cre-
ated a module that performed a countdown operation. If you wrote that
module generically enough, you could write other modules that exploited the
countdown capability in different ways. You might, for example, write one
program that displayed a countdown in Roman numerals and another that
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used Thai numerals, both based on the same abstract underpinnings. You’ll
often note that C and C++ programs consist of more than one file. There’s
usually a primary executable, then several libraries. Windows uses dynamic
link libraries (DLLs) most of the time; other platforms use static linking
arrangements.
C and C++ both have large communities of developers using them, which
means there’s a large body of prewritten C and C++ code out there (both for
sale and in the public domain). An increasing amount of the prewritten code
has to do with communicating information over networks, so it’s fair to say
that the languages are network friendly. However, they don’t support cross-
platform development like Java does. If you compile a C program for
MacOS, it’s a MacOS program forever.
General-Purpose Scripting Languages
A scripting language is any language whose code is not compiled. Further,
scripting languages rely on a host to interpret their programs and provide an
environment for them to operate in. The host can be an operating system
(most operating systems support at least one scripting language) or a stand-
alone program (most programs’ macro languages are examples of scripting
languages).

Because they’re easy to learn (relative to full-featured programming lan-
guages) and so well suited to quick-and-dirty solutions to problems, an
awful lot of server site activity is coordinated by programs written in general-
purpose scripting languages. Oftentimes, developers will use an operating
system’s native scripting language (shell scripting) or install and use a more
capable (or more attractive) scripting language like Perl or Tcl.
Shell Scripting
Because of the need of users and administrators to automate miscellaneous
tasks, most operating systems have a shell scripting language. A shell script-
ing language is a programming language (usually a fairly simple one) that
can issue command-line instructions, manipulate files and directories, do
some text management, and invoke other programs. The MS-DOS batch
language (which lives on in Windows NT 4 and elsewhere) is an example of
a shell scripting language.
Users of Unix variants can typically install any of several shells on their
machines to provide different sets of commands and different capabilities.
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Understanding Programming Languages 351
These shells—csh, ksh, and bash are some examples of Unix shells—have their
own shell scripting languages. Microsoft Windows 98 is the first Microsoft
operating system in some time to have a decent shell scripting language. Its
Windows Script Host (WSH), available as a retrofit for Windows NT 4 and
slated to be standard equipment on all versions of Windows 2000, allows you
to perform shell scripting tasks with JavaScript, VBScript, or any other script-
ing language for which someone makes available a WSH language module.
For Web developers, shell scripting languages are suitable for certain user
interactivity tasks. You could use your shell scripting language to take infor-
mation from a form and store it in a file or to assemble somewhat customized
pages for users to view. Still, compared to Perl, shell scripting languages are
usually pretty weak.

Perl
The darling of system administrators and Web developers everywhere (as
well as one of the greatest triumphs of the open-source movement), Practical
Extraction and Reporting Language (Perl) is like a good video game: easy to
learn, but hard to master. The odds are excellent that if the task you have in
mind can be accomplished at all, it can be accomplished with Perl. Server-
side scripts written in Perl may not run as fast as compiled programs or
exhibit the elegance of object-oriented programs, but they get the job done
and usually can be written in a hurry.
Perl excels at text processing, which means it’s great at picking informa-
tion out of form submissions and very good at assembling custom Web pages
in response to surfer requests. Its various modules—there are many—pro-
vide Perl programmers with easy access to many different environments,
including all popular server-side databases. Plus, it’s free. Larry Wall and a
community of developers have released Perl to the public domain and con-
tinue to develop it for the public benefit. Though Web developers are mainly
concerned with command-line Perl programs that interface with remote
Web clients, the language also can be used in conjunction with the Tk graph-
ical user interface (GUI) toolkit to create programs with graphical interfaces.
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The best way to learn about Perl is to install it and play with it yourself. You
can download the Perl tools (in source code form and in various compiled
forms) from many sites, including the Comprehensive Perl Archive Network
(CPAN) at www.cpan.org/.
Tcl
The Tool Command Language (Tcl) is a scripting language designed as a sort
of glue with which to share information among applications. Pronounced

“tickle,” Tcl was developed by John Osterhout. Like Perl, Tcl can work with
the Tk GUI toolkit to create windowed applications. You’ll often hear the
two referred to collectively as Tcl/Tk. Tcl isn’t as big a deal for Web devel-
opment as Perl and shell scripting languages.
There’s a collection of Tcl FAQs on the Web at www.tclfaq.wservice.com/
tcl-faq/. John Osterhout started a Tcl-related company called Scriptics; its
Web site is www.scriptics.com. You can download the Tcl development envi-
ronment there.
Web-Specialized Server-Side Scripting Languages
A server-side scripting language is any language whose code is embedded in
text documents and meant to be interpreted by the Web server program
before it sends the documents (typically containing HTML and server-side
scripting, as well) out to the client. Server-side scripts can, for example, insert
the current date and time in a document, customize a document with the
user’s name, or insert a hit counter.
Server-side scripting languages can sometimes work with arguments,
which are extra pieces of data supplied with the client’s request for a docu-
ment. A client might, for example, request this document:
results.php3
This is a Hypertext Preprocessor (PHP) program called results.php3. Pre-
sumably, this program yields output in a form the client can understand—
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Understanding Programming Languages 353
typically HTML. A client might also specify an argument by specifying
this file:
results.php3?physics
That causes physics to be available to results.php3 as the value for one of
its variables. Such a system might power a search engine, for example.
Hypertext Preprocessor (PHP)
Deriving its abbreviation from its German spelling, Hypertext Preprocessor

(PHP) is a public-domain server-side scripting language. It originally was
developed for Unix systems and continues to find most of its applications
under Apache servers, but a version of the language for 32-bit Microsoft
Windows machines is available, too. Get the details at www.php.net.
Active Server Pages (ASP)
Active Server Pages (ASP) is the server-side scripting solution for Microsoft
Web servers—mainly, Internet Information Server (IIS). If you’re running a
Windows NT server as your platform for Web content and need the versa-
tility of server-side scripting, ASP probably is the way to go. It’s based on
VBScript and you can use Microsoft Visual InterDev to automate some of
the development process. Get the details at msdn.microsoft.com.
LiveScript
LiveScript is the server-side scripting solution for Netscape Communications
Corporation’s Web servers. Essentially, it’s a variant of JavaScript—often,
you will in fact hear it called “server-side JavaScript.” Get the goods on this
language at devedge.netscape.com.
Client-Side Markup Languages
A client-side markup language is any system of adding tags (markup) to a
text document to supply information about how the text should be rendered
or what it means. Client-side markup languages are interpreted by the
browser, so you’ll sometimes see subtle variations in how different browsers
interpret the same markup.
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Hypertext Markup Language (HTML)
Hypertext Markup Language (HTML) is the most popular language for cre-
ating Web documents. With fundamentals that are easy to learn and high-
end capabilities that satisfy many advanced publishing requirements, HTML

is the workhorse of Web publishing. HTML code is not always elegant, it
does not lend itself to searching (the way XML does), and different browsers
will frequently interpret the same HTML document differently, but at
present HTML is the standard language of Web publishing.
A basic orientation to HTML coding appears later in this chapter.
eXtensible Markup Language (XML)
While HTML describes how its surrounding text should appear in a browser
window, eXtensible Markup Language (XML) describes what the text
means. Rather than lock publishers into a universal set of tags that must be
made to apply in all situations (as HTML does), XML allows users to define
their own tags as needed.
The idea is that, within a given group of XML users—people in a given
industry, say, or people wanting to communicate corporate financial infor-
mation to shareholders—there would be a common XML specification
called a document type definition (DTD). One party could publish data in
conformance with that DTD, and another party, having access to the same
DTD, could interpret it.
Remember, XML isn’t so much about the display of data. An XML doc-
ument on its own, in fact, is not renderable—you have to supply style sheets
and other information in order to associate the data in an XML document
with cosmetic characteristics a browser could use. For this reason, XML is
as much a data-interchange tool for communicating data among applica-
tions as a language for displaying data to a person.
Virtual Reality Markup Language (VRML)
Still primarily a novelty, Virtual Reality Modeling Language (VRML) is a
way of describing three-dimensional space via tags in a text document.
VRML includes means of describing shapes, relative positions, surface tex-
tures, and light sources.
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Understanding Programming Languages 355

Although it’s technically astute, fun to play with, and the center of a con-
siderable community on the Internet, VRML really hasn’t found a killer
application yet. It’s a minor publishing language.
Client-Side Scripting Languages
A client-side scripting language is a scripting language whose code is inter-
preted on the client side of the client-server relationship. Client-side scripting
code typically is embedded in HTML documents. It’s not executed when the
server runs the server-side code. Instead, it’s run by the client computer after
the download is complete. Client-side scripting languages can provide ani-
mation and interactivity (such as form prevalidation and simple calcula-
tions) without adding to the server’s processing load.
There are two main client-side scripting languages:

JavaScript and JScript (technically two languages, but very
similar ones)

VBScript
This section explores these languages.
JavaScript and JScript
JavaScript is a powerful yet fairly simple scripting language you can use to
add “intelligence” and interactivity to your Web pages. With JavaScript, you
can do such things as:

Make your browser’s status bar display a label when you pass your
mouse pointer over a link

Design a registration form that makes sure visitors to your site send in
valid information

Equip your pages with animated elements

JScript is Microsoft Internet Explorer’s version of JavaScript. It can handle
any JavaScript program…more or less. Though JScript is mostly compatible
with JavaScript, Microsoft Internet Explorer doesn’t interpret everything the
same way Netscape’s browser does. The lesson to you: test your pages with
Microsoft Internet Explorer as well as Netscape Navigator.
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Here’s an HTML document that incorporates a simple JavaScript pro-
gram, just to give you an idea of the basic syntax:
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
</HEAD>
<BODY>
<H1>Say hello to the nice reader...</H1>
<SCRIPT LANGUAGE=”JavaScript”>
<!--
document.write("<P>Hello, network!")
// -->
</SCRIPT>
<H1>Very good!</H1>
</BODY>
</HTML>
Figure 8.1 shows what the code looks like when interpreted by a browser.
Note that the document.write() statement results in text that looks like an
integral part of the HTML code.
FIGURE 8.1 The results of a simple JavaScript program
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Understanding Programming Languages 357
VBScript
If JavaScript borrows much of its structure and syntax from Java, VBScript
borrows a great deal from Visual Basic. As Microsoft’s preferred client-side
scripting language, VBScript can do all sorts of automation, animation,
verification, and organization jobs on the client side. If you know standard
Visual Basic, you’ll probably find it easy to pick up a working knowledge
of VBScript. In fact, you can use your VB development environment to do
many VBScript development tasks.
Here’s a simple VBScript program to give you a feel for the language’s
appearance:
<HTML>
<HEAD>
<TITLE> Hello </TITLE>
</HEAD>
<BODY>
<H1>A VBScript Demonstration</H1>
<INPUT TYPE=BUTTON VALUE="Say Hello" NAME="Hello">
<SCRIPT LANGUAGE="VBScript">
<!--
Sub Hello_OnClick
MsgBox "I want my i-Net+ certification!", 0,
"VBScript Demonstration"
End Sub
-->
</SCRIPT>
<H1>Very good!</H1>
</BODY>
</HTML>
Figure 8.2 shows what this code looks like in Microsoft Internet Explorer

(which is the only browser, by the way, with native capacity to interpret
VBScript). The subroutine executes only when the user clicks the button.
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FIGURE 8.2 A simple VBScript program that spawns a dialog box
Databases
A
database is any collection of data. A card file is a kind of database;
a list of telephone numbers on a piece of paper is a database. Computer data-
bases are essentially the same sorts of things, but with the information (and
the labels identifying it) stored digitally.
Database Management Systems (DBMSes) are programs that add data to
databases, extract data from them, organize the data for various applica-
tions, and generally attempt to guarantee that the database is fast, easily
accessible, and secure from outsiders. Data mining applications attempt to
analyze the data in databases and draw conclusions from it. Data mining
applications at Wal-Mart Stores, Inc., for example, realized that most people
who buy breakfast cereal at Wal-Mart also buy bananas during the same
visit. The result of the data mining is that most Wal-Marts now stock
bananas in their cereal aisles, hoping to encourage even more cereal buyers
to pick up some bananas on impulse.
Non-Relational Databases
Non-relational databases (or flat-file databases) are essentially unadorned
lists. A non-relational database might serve to correlate names with e-mail
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Databases 359
addresses or atomic symbols with atomic numbers. Non-relational data-
bases play a big role in the operation of the Internet because they store the

Domain Name Services (DNS) lists that associate domain names with IP
addresses.
The problem with non-relational databases is that they can’t keep track of
sets of data with multiple relationships among the fields. Non-relational
databases that are used to keep track of data with such complex relation-
ships end up having multiple instances of each piece of data—an inefficiency
that’s one of the cardinal sins of database design. Relational databases are
better for applications that involve complicated relationships.
Relational Databases
A relational database is a database with multiple tables, each having some-
thing in common with at least one other. Say, for example, that you work for
your government’s automobile-registration organization. You might have
one table that correlates license plate numbers to Vehicle Identification
Numbers (VINs) and another table that correlates VINs with the registered
owners of the vehicles those VINs represent. Still another table might con-
tain contact information about the people who have registered vehicles with
your government.
So, if the police want to find the address of the woman who just held
up the liquor store in your town, they’d go to the motor vehicle authority
with the license plate number of her getaway car. The doughty database
administrator there would be able to find the robber’s name and address by
associating the plate number with a VIN, the VIN with a name, and the name
with an address. There are three tables involved, all related to one another by
some common piece of information. This is a relational database.
Database Servers
A database server is any program that’s responsible for maintaining one or
more databases and responding to queries sent to them. Database servers
combine efficient storage and access with DBMS software. All major data-
base servers comply with the Structured Query Language (SQL) specifica-
tion—more on that later—though many of them supplement standard SQL

with proprietary or otherwise nonstandard extensions to the language.
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In addition, a computer that’s dedicated to running a database server pro-
gram is called a database server.
Many companies publish database server software. They all have their
fans. Some fit better into certain applications than others; some cost more
than others. Evaluate the companies’ offerings next to your organization’s
needs. Here are the big players, in alphabetical order:

Hughes Technologies puts out mSQL, a server for small- and mid-size
applications that’s free for use under certain circumstances. Read
about it at www.hughes.com.au/.

Microsoft publishes Microsoft SQL Server 7, which runs best under
Windows NT. Details are at www.microsoft.com/sql/.

Oracle made its name with database servers. Its latest products are the
servers of the Oracle 8I family. Details appear at www.oracle.com/
database/oracle8i/.

Sybase also has been selling database servers for years. Its latest ones
compose the Adaptive Server family. Read all about them at www
.sybase.com/products/databaseservers/.

T.c.X DataKonsult improved upon mSQL and came out with
MySQL, which also is free under some circumstances. The server has
a Web site: www.mysql.com/.

Structured Query Language Fundamentals
Structured Query Language (SQL) is the standard language for working
with relational databases. It’s a complex, powerful language that’s far
beyond the scope of this book and the i-Net+ exam, but its fundamentals are
worth a mention here.
SQL is a descriptive language, which is a kind of language different from
the procedural and object-oriented languages that characterize most soft-
ware development jobs. Here’s an analogy. Say you went to a delicatessen to
acquire a ham sandwich. If you were only able to speak in procedural lan-
guages, you’d have to tell the guy exactly what to do in order to yield the
results you wanted. You’d have to say, “Cut the roll in half and place the
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HTML Fundamentals 361
halves side-by-side, cut side up. Spread mustard on the halves. Slice ham
until you have a quarter-pound of it. Remove the ham from the slicer….”
You get the idea.
With a descriptive language, you could just describe the results you want.
“I want a ham sandwich on a Kaiser roll with Dijon mustard and an olive,”
you’d say. And then the counterman, being a skilled maker of sandwiches,
delivers what you want. The process is a lot easier. In the case of databases,
the database server knows how to extract information from the databases it
knows about. Clients who make requests for data from the databases
describe the data they want with SQL. These requests are called queries.
Let’s take a look at an example of an SQL query:
SELECT firstName, lastName FROM employeeTable;
That query would yield a list—called a report—of all values in the firstName
and lastName fields of every record in the employeeTable table. What if we
didn’t want all of them? We could try this:
SELECT firstName, lastName FROM employeeTable
WHERE wage > 8.5;

That would yield the contents of the firstName and lastName fields in every
record in which the wage field contained a value greater than 8.5.
Note that queries don’t have to extract data from databases. The SQL
instructions that create tables, insert data into them, and establish relation-
ships (called joins) among tables are called queries, too.
There’s a good SQL tutorial on the Web at w3.one.net/~jhoffman/
sqltut.htm.
HTML Fundamentals
M
ost Web publishing involves Hypertext Markup Language
(HTML) to some degree or another. This section aims to orient you to the
barest fundamentals of the language. Detailed coverage of HTML is beyond
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