Day 1 -- Introducing VBScript and the World
Wide Web
DAY 1
Introducing VBScript and the World
Wide Web
CONTENTS
The Internet and the World Wide Web
Browsing the World Wide Web
Mosaic
Netscape Navigator
Internet Explorer
Other Browsers
The Elements of the World Wide Web
TCP/IP: The Way Data Moves Through the World Wide Web
HTTP: The Way Data Is Transported Through the World Wide Web
HTML: The Language of the World Wide Web
Extending the World Wide Web with VBScript
Microsoft ActiveX and ActiveX Controls
Extending the World Wide Web with CGI
Summary
Q&A
Workshop
Quiz
VBScript. Maybe you've heard it's a tool that lets you
build more powerful Web pages. Perhaps you've heard it called
the "JavaScript killer" because it's easier to use.
You might simply know it as an Internet buzzword. Whatever your
motivations, the fact that you're reading this book indicates
that you want to know what VBScript is all about.
You've come to the right place! VBScript is an exciting, powerful
tool at the center of the rapid Internet information revolution.
In this book, you will find everything you need to know to get
started. Before you start learning about how VBScript works, you
should know a little bit about how the Internet phenomenon began
and how VBScript fits into the big picture. It's so easy to get
lost in a sea of terminology and acronyms. This lesson cuts through
the jargon and helps prepare you for the exciting journey ahead
of you-understanding and learning how to use VBScript to its fullest.
Questions answered in this lesson include the following:
What is the Internet, and why is it so popular?
What is the World Wide Web, and how does it fit in to the
Internet?
What are Web browsers, and how are they used?
What are the most popular and widely used browsers available
today?
What are Web pages, and how are they created?
What is Microsoft's ActiveX technology, and how does it relate
to the Web?
How does VBScript fit in when creating a Web page?
What are Java and CGI, and where do they fit in?
How are Web pages sent over the Internet?
If you are already familiar with these concepts, you might want
to skip ahead to Day 2, "The Essence
of VBScript," which discusses how VBScript and Hypertext
Markup Language (HTML) work together with the Web browser to present
a Web page to the user.
The
Internet and the World Wide Web
The Internet, which has come to serve over 20 million users worldwide,
had relatively humble beginnings. It began as a rather obscure
network called ARPANET-a network used by the Department of Defense,
its contractors, and defense researchers. The ARPANET proved very
useful and powerful, so much so that over time it grew tremendously.
Soon, a more general network called the Internet was created with
the same philosophy as ARPANET, only with a broader scope. In
the late 1980s, the Internet spread across universities around
the world and became more and more popular among researchers in
the academic community.
As the popularity of the Internet increased, so did its size.
Starting in its earlier days, users became increasingly aware
of the benefits of specific services such as electronic mail and
the ability to transfer files. Over time, the incredible potential
of the Internet for sharing and distributing information became
apparent as more and more people started using it. The National
Science Foundation, which had almost completely funded the Internet
in the United States until 1991, lifted its ban of commercial
traffic on the Internet in 1991 and dropped most of its funding.
This gave the Internet much more widespread exposure and opened
the door to many more commercial ventures. Since then, the Internet
has grown in incredible proportions. Given the current and potential
growth of the Internet, you can't afford not to learn about the
Internet, especially if you are a part of corporate America.
Now that corporations and the telecommunication giants are becoming
more interested in the Internet, the Internet is maturing at an
unprecedented rate. Organizations ranging from product vendors
and standards bodies to the National Science Foundation, which
helps support the backbone of the Internet that carries all of
the information between the Internet and its hosts, are developing
standards and security mechanisms that should take the Internet
to new heights. Consider, for instance, the capability to receive
real-time voice and video so that you can see the person you're
talking to or the capability to order a pizza and watch a movie
using the Internet. The possibilities are unlimited. Your ability
to leverage its benefits for your company or personal use will
become increasingly valuable as the Internet is exposed to more
and more people across the world.
What is the Internet, really? The Internet, simply put, is like
a vast ocean of computers across the world connected together
by a network of cables. Figure 1.1 shows a simplified diagram
of how the Internet is constructed.
Figure 1.1 : A simplified view of the Internet.
Because all these computers are connected as shown in Figure 1.1,
a computer connected to the network can gain access to any of
the others, providing a seemingly infinite amount of information
to the user. Suppose, for example, that you are a bird lover who
lives in Detroit. You want to get information on how to teach
your cockatiel to sing. A computer down in Miami has just what
you want-a bird lover's consortium, where people all over the
world come to share information about birds. Using the Internet,
you could connect to that computer as Figure 1.2 shows.
Figure 1.2 : Internet connection to the bird consortium.
In this example, your computer sends information from your computer's
modem, through your telephone line, out to a series of cables
that provide access to all of the computers on the Internet. The
Internet simply has to route the information from your computer
to the computer in Miami-the one you want to access. As long as
the Internet provides a valid route, you can send and receive
information from this specific computer. If you want to exchange
information with another computer in addition to the one in Miami,
you are free to do so. The Internet provides this capability for
you; all you need to know is the address of the computer
you want to exchange information with. The Internet does all the
rest.
An Internet address is used to identify a computer connected
to the Internet. Every address must be unique, since the computer
represented by that address is unique to the Internet. Names are
registered through the Network Information Center (rs.internic.net)
to ensure uniqueness. Internet addresses can be represented in
terms of textual domain names, such as www.doubleblaze.com;
or in terms of the corresponding address, called an IP address,
such as 205.132.48.237. Uniform
resource locators, or URLs, incorporate Internet addresses
to indicate the network location of a Web page or other network
resource.
The details of the illustration could vary because there are so
many different possible routes to connect one computer to another
on the Internet. If, for example, you are at work or school rather
than at home, you might already be at a computer directly attached
to the Internet. In that case, connecting with a modem might not
be necessary. Furthermore, once you're on the Internet, you can
trade information using a variety of approaches ranging from Web
browsers or electronic mail to transferring files.
How do people use the Internet? The Internet is used for sending
and receiving electronic mail, exchanging files, reading and participating
in news groups, and obtaining information in general. In the bird
consortium example, you have a variety of options at your disposal
once you're connected to the Web site. You can browse a Web page
filled with information on cockatiels or participate in a news
group discussion of cockatiel mating habits. You might find a
reference to a public file containing research on cockatiel schizophrenia
and then download the file to your computer. You could even send
e-mail to the president of the National Cockatiel Mating Society,
given the correct address. Well, you get the point.
The best way to describe the Internet is to list the services
it provides. The Internet has a wide variety of services available
to the user. Often, a service on the Internet is called a protocol.
A protocol is simply a set of rules for communication. Each
service has its own special set of rules to accomplish its goals
more easily. The following list describes some of the major services:
A protocol is a set of rules for communicating across the
Internet. Both parties know and follow the rules for sending and
receiving information, making meaningful communication possible.
Electronic mail: E-mail is a very simple and direct way to
exchange messages targeted for particular users on the Internet.
File Transfer Protocol (FTP): This protocol enables users
connected to the Internet to exchange files with other users by
sending them to and receiving them from Internet sites.
Telnet: This protocol enables a user to connect to another
computer on the Internet. With the appropriate privileges, this
protocol could, for example, allow you to connect to the university's
administration computer from the computer in your dorm room and
then enter commands that are carried out on the administrative
computer (such as changing all your grades to A's).
Gopher: This protocol enables Internet users to access topical
information from servers that support the Gopher protocol. This
protocol, along with Telnet and FTP, is among the older protocols
of the Internet. One of the services Gopher provides is the ability
for users to search for information on the Internet by providing
a list of news group topics. Users can then quickly and easily
access the news groups of their choice from this list.
Hypertext Transfer Protocol (HTTP): This protocol, the backbone
of the World Wide Web, enables users to send and receive information
from Internet servers in the form of documents, or pages, written
using the Hypertext Markup Language (HTML). The user who receives
the document, often called the client, can then use a browser
or other form of software that recognizes the HTML language
to view the contents of the document. Through a browser, the user
can even access some of the other protocols, such as Telnet or
FTP. HTTP and the World Wide Web can thereby facilitate access
to the important protocols under one easy-to-use interface. If
the user wants maximum flexibility in FTP file exchanges, he'd
likely use the FTP protocol directly. On the other hand, the user
can browse Web pages and easily locate FTP files from within the
familiar browser interface if no advanced use is needed. This
ease of use in sharing Web page information and working with the
Internet protocols has been central to the widespread acceptance
and popularity of the World Wide Web.
A browser is a software program used to view HTML documents
within the World Wide Web.
The World Wide Web is by far the most talked-about service on
the Internet today. As you can see, it is only one of many services
available to the user. This goal of this book is to teach you
how to use VBScript to enhance Web pages. Because Web pages are
used within the World Wide Web, we will be focusing on this Internet
service. If, however, you want your users to have access to these
other services from within your Web pages, you should become familiar
with the other protocols as well. Suppose, for example, you want
to be able to initiate an FTP session so that the user of your
Web page can transfer a file; before you can do so, you need to
know what FTP does and how to use it. You can learn more about
these other Internet services and the Internet in general by reading
The Internet Unleashed 1996 by Sams.net Publishing.
The World Wide Web is an information system that brings together
data from many of the other Internet services under one set of
protocols. The World Wide Web began in March 1989 when a group
of high-energy physics researchers wanted a new protocol for
distributing information on the Internet. The European Laboratory
for Particle Physics, or CERN, actually proposed the standards,
and a consortium of organizations, called the W3 Consortium, was
created for continuing to develop the standards. The consortium
put together a set of protocols for the World Wide Web by creating
the Hypertext Markup Language, or HTML. HTML is the underlying
standard and means by which information is exchanged in the World
Wide Web. In addition, various browser developers, most prominently
Netscape and Microsoft, have at times extended HTML with their
own additions. Essentially, the World Wide Web consists of HTML
documents, or Web pages, which are delivered by Web servers and
can be interpreted by Web clients, or browsers. The next
section discusses the Web clients that actually interpret these
HTML documents for the user.
Browsing
the World Wide Web
As was stated in the previous section, users view information
within the World Wide Web by using Web browsers. Before you begin
designing the Web pages themselves, you need to be acquainted
with the tools people use to view them. Users who access the Internet
are not limited to a specific type of computer. It's no surprise,
then, that a wide variety of computers and operating systems are
supported by Web browsers, including Windows for personal computers,
Macintosh for Apple's Macintosh computers, X Window for UNIX systems,
and more. How does a browser work? The primary goal of a Web browser
is to send and receive data from the Web server that provides
the Web page. The underlying markup language used to define the
content of pages in the World Wide Web is HTML. Therefore, the
server sends the Web page in the HTML markup language, and the
browser interprets that HTML code, presenting the page to the
user. The next section discusses HTML in detail. Right now, take
a look at the most commonly used browsers available today.
Mosaic
Mosaic, created by ncSA at the University of Illinois, was the
first full-color, graphical browser available for the Internet.
Because it was the first of its kind, Mosaic was the first glimpse
many users got of the World Wide Web and likely fired the imagination
of many a potential Web page designer. Before Netscape was introduced
and dominated the market, Mosaic was the most popular browser
available. Figure 1.3 shows a Mosaic session in Microsoft Windows.
Figure 1.3 : Mosaic for Microsoft Windows.
Like most browsers today, Mosaic supports all of the popular Internet
services, including FTP, Gopher, and Telnet, just to name a few.
Mosaic is available for Microsoft Windows, Macintosh, and X Windows,
titled WinMosaic, MacMosaic, and XMosaic, respectively. At the
time of this printing, you can obtain each version via FTP at
ftp://ftp.ncsa.uiuc.edu/Mosaic.
Netscape Navigator
Netscape Navigator, created by Netscape Corporation, is by far
the most popular browser available today. One of the primary reasons
for its success is that it is considerably faster than Mosaic,
the once dominant browser. It also provides additional features
that Mosaic does not have. Netscape is available on Windows, Macintosh,
and X Windows platforms. Figure 1.4 illustrates the main screen
of a Netscape session.
Figure 1.4 : Netscape for Microsoft Windows.
Netscape is one of several browsers currently available that supports
the Java language. The most recent version of Netscape contains
specific extensions to HTML that provide much more control over
the look and feel of a Web page. Many of these extensions were
initially only supported by Netscape, although Microsoft's Internet
Explorer 3.0 now supports many as well. Programmers who design
Web pages using these extensions must remember that they will
not operate with browsers that do not support them. At the time
of this printing, you could obtain the latest copy of Netscape
directly from the Netscape Communications FTP sites. Due to the
popularity of this browser, there are almost 20 FTP sites available
for downloading the Netscape browser. The addresses are ftp://ftpx.netscape.com/,
where x is
a number from 2 through 20, depending on the site you wish to
access.
Internet Explorer
Internet Explorer is Microsoft's contribution to the Web browser
community. The Internet Explorer is based on Microsoft's ActiveX
technology and is available for Windows, Windows NT, and Macintosh
platforms. As this browser gains acceptance while Microsoft expands
its Internet efforts, Internet Explorer might challenge Netscape
for domination of the browser market for Windows users. One significant
capability of the Internet Explorer is that it supports embedded
intrinsic and ActiveX controls within Web pages, which VBScript
can interact with. This very important characteristic will be
expanded upon in Days 8, "Intrinsic
HTML Form Controls," 9, "More
Intrinsic HTML Form Controls," 10,
"An Introduction to Objects and ActiveX Controls," and
11, "More ActiveX Controls."
Figure 1.5 shows Internet Explorer at work.
Figure 1.5 : The Internet Explorer Web browser.
Microsoft's Internet Explorer was the first browser to support
VBScript. As a result, Internet Explorer is used for most of the
examples in this book. If you don't already have a copy, you should
obtain one. Here are the steps you should follow to do so:
First, download and install Microsoft's Internet Explorer
3.0. At the time of this printing, Internet Explorer 3.0 was still
in beta and was available at http://www.microsoft.com/ie.
Microsoft plans to provide Internet Explorer 3.0 with the Windows
95 Upgrade Pack slated for release in the fall of 1996. Until
then, Microsoft's working beta is the only option available, and
you must connect to Microsoft's Web site to download it.
In order to use ActiveX controls together with VBScript for
the examples in this book, you must have access to the ActiveX
controls used. Pages can be constructed to download the required
controls from Microsoft's server when needed. To use the examples
in this book with the beta Internet Explorer 3.0 you should initially
run the "requirements check" page on the CD-ROM to obtain
all the required controls at one time. Microsoft plans to provide
a complete suite of ActiveX controls with the Windows 95 Upgrade
Pack slated for release in the fall of 1996. Until then, Microsoft's
working beta is the only option available, and you must connect
to Microsoft's Web site to download it and the corresponding controls.
Note
Be sure you have Internet Explorer Version 3.0. Earlier versions of Internet Explorer do not support VBScript.
Note
Make sure you have the latest version of ActiveX controls on your system when using VBScript. Earlier versions of the ActiveX Controls may not work properly with the latest version of the Internet Explorer and VBScript.
The Internet Explorer capabilities are expected to eventually
become an integrated part of future Microsoft Windows operating
environments, and the underlying Internet services it requires
will be built directly into the operating system. This means that
in the future every user of Microsoft Windows will have easy access
to these browser features and the corresponding VBScript support.
This is one of the reasons that the Internet Explorer browser
is viewed as a very strategic development platform when targeting
Web page development, even though it currently has a significantly
smaller share of the market than the Netscape browser.
Other Browsers
A variety of additional browsers are available, and because the
Internet is evolving so rapidly, other new browsers may have come
into existence since this book was printed. The core language
capabilities of VBScript should be consistent under any browser
that supports it because the definition of the language doesn't
change and isn't dependent on the browser. However, VBScript can
take advantage of the browser environment objects as well, and
this may vary from browser to browser. The only requirement is
that the browser supports VBScript. For any browser developer
or provider who makes the request, Microsoft will provide a free
license to the VBScript run-time interpreter and even the source
code so that they can make their browsers recognize and cooperate
with VBScript. If you want more information on these efforts,
refer to the VBScript white paper located on Microsoft's VBScript
Web site, http://www.microsoft.com/vbscript.
You can also refer to The World Wide Web Unleashed 1996
(Sams.net Publishing) to learn more about other popular Internet
browsers.
The
Elements of the World Wide Web
The overall concept of the World Wide Web is an easy one to grasp
once it's had some time to sink in. If you're a newcomer to the
Web scene, getting the first, clear glimpse of the concepts can
be a challenge! You've heard the old saying, "A picture's
worth a thousand words." That's especially true when these
words are an alphabet soup of protocols, buzzwords, and technologies.
If you consider the simple analogy that follows, the concept of
the World Wide Web should quickly come into focus. (See Figure
1.6.)
Figure 1.6 : Sending a Web page to a client.
The two docks have a ship sailing from one dock to the other.
The dock on the left is referred to as the "server dock"
and the one on the right is the "client dock." The owner
of the client dock wants to get some cargo from the server dock.
The owner of the client dock sends over a ship and tells the captain
of the ship to ask the server dock for a specific type of cargo.
Once the ship gets over to the server dock, the worker on the
server dock that handles such requests-the "Web server"-loads
up the cargo that the client wants. The worker on the server dock
knows that special unloading and handling will be needed once
the cargo arrives at its destination, so he attaches those instructions
to the cargo. Then, the ship sails on its way back over to the
client.
When the ship arrives back at the client dock, a worker called
the "Web browser" unloads the cargo. It turns out that
the Web browser can unload cargo, but she doesn't know how to
read the special instructions. Fortunately for her, a couple of
assistants are on the dock to handle any special instructions
that come their way. The Web browser, along with the assistants,
JavaScript and VBScript, unloads the cargo and then presents it
to the owner of the client dock. The task is complete.
In real life, a similar sequence of events occurs. When you want
to see a Web page, for instance, you first load your browser and
then specify the name and address of the Web page you want to
view, often referred to as a uniform resource locator,
or URL. Once you've entered the URL, the browser connects to the
server on which that Web page is found and asks the server to
send over the Web page. Using the analogy, this is where the owner
of the client dock sends a ship to the server dock requesting
cargo. In the same way the cargo sits on the dock, a Web page
resides on a server. To send a copy of the Web page over to the
client, the Web page must travel across the Internet to the client.
In the analogy, you can't get the cargo from the server dock to
the client dock without two things-a ship to transport the cargo
and water for the ship to travel through. Likewise, data can't
get from one host to another on the Internet without a transport
mechanism and a pathway for that transfer to take place.
A uniform resource locator (URL) is an address that
identifies a resource on the Web.
As with any analogy, you can only take things so far. One thing
to keep in mind when using this analogy is that, in reality, a
Web page is not actually moved from one site to another. A copy
of the page is sent from the server to the client. Picture
an unlimited supply of stock on the dock where copies are lifted
onto the ship whenever requested. The inventory won't get depleted.
However, just as a dock can get very busy and arriving ships might
have to wait their turn, a busy server can get overloaded and
be slow in responding to Web page requests.
Now, take a look at each element of the Internet that works together
to get a Web page from a server to a client. It's really not that
complicated once you see how all the pieces fit together.
TCP/IP: The Way
Data Moves Through the World Wide Web
The water in the ship analogy is representative of the Internet's
means for communication, called the Transmission Control Protocol/Internet
Protocol, or TCP/IP. TCP/IP takes care of successfully routing
the information from one site to another. The beauty of the World
Wide Web is that you, the user, are shielded from most of these
inner workings. The protocol sets up an address for each site
called an IP address. The IP address consists of four 8-bit
numbers separated by dots and is sometimes called the dot address.
For example, the address of the Internet site that holds information
about this book and any late-breaking updates is 205.132.48.137.
An IP address typically identifies a network card to which a connection
is made; as a result, each IP address must be unique. TCP/IP also
establishes for every server entity on the Internet an IP machine
name. The name www.doubleblaze.com,
which corresponds to 205.132.48.137,
is one example of an IP machine name. The IP machine name is part
of the URL that you enter into your browser when you want to view
a Web page. When you type the URL, which includes the machine
name, into the browser, the name is resolved by returning an IP
address for the browser to connect to. All of this is transparent
to the user. All you have to do is enter the URL of the Web page
you want to see. Taken together, all the components of TCP/IP
work together to get you to where you want to go on the Internet,
much like the water in our analogy.
HTTP: The Way
Data Is Transported Through the World Wide Web
The ship in the analogy represents the Hypertext Transfer Protocol,
or HTTP. You typically enter http
as the first part of any URL on the World Wide Web. HTTP is the
protocol that enables Web clients and Web servers to communicate
over TCP/IP. HTTP consists of a set of rules by which data such
as HTML documents, represented by the cargo on the ship, gets
transmitted between Web clients and Web servers. The cargo carried
by the ship in Figure 1.6 can consist of Web pages, which are
HTML documents, as well as other data. It matters little to the
ship what type of cargo it is carrying; the job of the ship is
simply to get the cargo from one dock to the other without damaging
the cargo. Likewise, the goal of HTTP is to work with TCP/IP to
get the data from the server to the client free from corruption.
The Hypertext Transfer Protocol (HTTP) is a protocol
used to transfer HTML documents across the World Wide Web. HTTP
is the native protocol of the Web.
HTML: The Language
of the World Wide Web
As mentioned in the previous section, one type of cargo the ship
can carry is HTML documents. HTML documents, or Web pages, are
the most common type of cargo that HTTP sends through the World
Wide Web. It is easy to get HTML confused with HTTP. Keep in mind
that HTTP is the set of rules used to transport HTML documents
as well as other data. The analogy in Figure 1.6 should help you
to keep these concepts straight. We will explore the structure
of HTML much more in Day 2, where you will
learn how to embed VBScript code into an HTML document. Consider
the analogy once again: Once the cargo arrives at the dock, it
must be unloaded. This is the job of the attendant standing at
the dock-call that person the Web browser. This attendant presents
the cargo to the customer. Likewise, the real Web browser takes
the HTML code and makes it presentable on-screen to the user.
This is how the user is then able to see the Web page. HTML and
the information viewed by the user can be extended using ActiveX
controls, VBScript, and other languages such as JavaScript.
Extending
the World Wide Web with VBScript
In Figure 1.6, the Web page cargo has special unloading instructions
attached to it. These special instructions aren't written in a
language the Web browser can understand, so she can't handle them
directly. Fortunately, the Web browser has a couple of assistants
on the dock with her whose job it is to handle these special instructions.
When the cargo gets to the dock, the Web browser passes these
special instructions to the assistants, who in turn help her handle
the cargo.
In the ship analogy, these special instructions attached to the
HTML document represent the interpreters for scripting languages
such as VBScript and JavaScript. When you design a Web page, you
package these special instructions in the form of code inside
the HTML document. Then, when the Web page gets to the client,
the Web browser has to be able to recognize the special instructions
and have those assistants on-hand to process them.
JavaScript behaves similarly to VBScript in that it uses an interpreter
to take the special instructions and execute them on the client
computer. The scripting tools differ, however, in that JavaScript
is somewhat based on C/C++, whereas VBScript is based on Visual
Basic. Furthermore, each tool has a different set of features
and capabilities. A great number of Internet users who want to
develop Web pages and already use Visual Basic will find VBScript
extremely easy to use. Even those who have never used Visual Basic
will find VBScript easy to learn as compared to the more complex
C++-like language of JavaScript.
Microsoft
ActiveX and ActiveX Controls
In an effort to facilitate development of Internet Web pages and
applications, Microsoft introduced a set of standards, definitions,
and beta software components called the ActiveX Development Kit
in early 1996. This set of technologies marked a major technology
focus affecting many areas of World Wide Web-related client and
server technology as well as Windows itself. ActiveX is a framework
that includes VBScript, ActiveX documents, ActiveX controls, and
other layers and technology specifications as well. Within this
new framework, it is easy to make the once static pages on the
Web active. A page can essentially become a blend of HTML, embedded
JavaScript or VBScript, ActiveX controls, OLE controls, and Java
applets that the code language interacts with.
Microsoft's OLE (object linking and embedding) controls had been
in use in the Windows world for some time prior to the introduction
of the ActiveX terminology. OLE controls provide powerful, component-based
capabilities and are easily incorporated into other programs through
the OLE communication, control, data storage, and automation protocol.
The ActiveX control technology specification is the new generation
of OLE controls. While many ActiveX controls are being developed
specifically for Internet-related purposes, ActiveX controls are
not restricted to the Internet.
The ActiveX Internet client technology first appeared in Microsoft
Internet Explorer 3.0. VBScript is a part of this technology,
so it can interact with ActiveX controls. By taking advantage
of ActiveX controls, you can greatly extend the power of your
Web pages. Many ActiveX controls are available from Microsoft,
and any other developer can produce his own ActiveX controls.
The end result is a wealth of building blocks that you can blend
with VBScript into a powerful, active Web page. A significant
part of being an effective VBScript programmer, then, is knowing
how to leverage these controls.
Extending
the World Wide Web with CGI
Thus far, discussion has focused on scripting tools that reside
on the client's computer, interpreting special instructions intended
to extend the functionality of a Web page. In addition to residing
on the client, a certain type of scripting tool can also reside
on the server. Although scripting tools on the server serve a
different purpose from those on the client, they are often very
useful and sometimes necessary for advanced Web pages-for instance,
when a user has a Web page that enables her to perform a search
for pages that contain a keyword she supplies to the page. The
HTML document itself isn't capable of doing a search because it
doesn't know what's contained in other Web pages. Assume, however,
that the server contains an entire database of Web pages. It would
be convenient for the client page to have the server perform the
search and report back the results. Doing so requires that the
client request such a search from the server. The Common Gateway
Interface, or CGI, was created for that purpose. ISAPI, OLE
ISAPI, and IDC are somewhat similar technologies that can be used
with Microsoft NT Server scripts. For now, we'll limit the focus
to CGI, although the communication concepts described largely
hold true to the other technologies as well. Refer to the familiar
analogy of a ship sailing between two docks. The analogy so far
is based on the server sending out information to the client in
response to standard requests for cargo. In this case, however,
you want the client to request from the server special information
that must be custom-made. Once the server creates this cargo,
it sends it to the client. The server can either send a standard
Web page or special information requested by CGI that the server
creates. Figure 1.7 shows the modified analogy.
Figure 1.7 : Sending a CGI script to the server.
The Common Gateway Interface (CGI) is a standard that allows
programs to interface with the Web servers. This gives Web users
the ability to interact with Web server programs in order to accomplish
useful tasks such as database storage and retrieval.
In this case, the Web browser places the request for special cargo
on the ship, the ship then transports the request to the Web server,
and the Web server unloads the request and passes it on to CGI
for special processing. Once CGI gets the request, it determines
the application it needs to call and calls it. Sometimes, the
application is like a toolbox that enables the Web server to handcraft
brand new cargo to send back to the client. The application gets
the data and returns it to CGI, which then passes the results
over to the Web server. The Web server then takes the results
and passes them back to the Web browser.
CGI, like HTTP, is a protocol that is explicitly designed to interact
with an HTTP server. Through a CGI request, the client can request
that the server start a CGI script or application, pass parameter
data to it, and then return the result from the application. CGI
scripts can be written for a variety of servers with languages
such as Perl, TCI, or the UNIX shell for UNIX-based platforms.
On many Windows-based HTTP servers, a CGI extension layer called
WinCGI also makes it possible to call Visual Basic programs. ISAPI,
OLE ISAPI, and IDC are other high-performance technologies that
can be used for NT Server scripting solutions. OLE ISAPI, like
WinCGI, makes it easy to build a Visual Basic program that serves
as a server-side script. All such scripting tools work very closely
with HTTP servers. Once the server application has done the required
work and obtained results, those results can be passed back to
the client as HTML text. The server must therefore be able to
exchange information with both the client and the application
on the server using the CGI protocol.
CGI makes it possible for Web page users to ask the server to
perform operations not available to the client. In order to maintain
security, VBScript can only perform operations within the Web
page; it cannot, for example, store data on the client, nor can
it directly store data back on the server to a remote database.
Typically, a Web page will rely on CGI services to get data back
to the server. On the server's end, CGI capabilities complement
the processing of VBScripts on the client's end. For example,
a VBScript might process and validate user input, and then CGI
might be used to store that data in the host database on the server.
As you can see, CGI and similar technologies offer a very powerful
capability to make pages interact with the server. As you learn
to use VBScript, you will begin to see the potential for such
technologies as they work together with VBScript to enhance a
Web page. With the combined power of VBScript and CGI or ISAPI,
the programmatic possibilities behind a Web page are virtually
unlimited!
Note
The term script is commonly used in several contexts when talking about Web pages. VBScript can be used to build "intelligent" Web pages that carry out processing on the user's computer when the user views a page. JavaScript offers similar
capabilities. These are called Web page scripts.
You can also have server-side scripts that carry out action on the server where the Web page files reside. These server-side scripts can be triggered into action by actions on the user's computer when viewing a page, if a page is set up accordingly.
Regular Visual Basic (that is, Visual Basic 4.0), among other languages, can be used to write such server-side scripts. It can be expected that eventually VBScript will also be supported on the server and can be used to provide server-side scripting.
The focus of this book is on Web page scripts written in VBScript for the Internet Explorer browser environment. However, the information presented here about VBScript will be of use in dealing with scripts in other environments as well.
Note
This book is based on the beta release of Internet Explorer 3.0. Certain features may change with the release of the final product. Late-breaking update information on the final product may be available under the Macmillan Publishing site www.mcp.com (then follow the Sams.net selections). This information may also be found under the CNS server at www.doubleblaze.com/vbs21day.
Summary
The Internet is an exciting forum that makes it possible for users
to access virtually an infinite supply of information. This lesson
presents you with an overview of the Internet and, specifically,
the World Wide Web. Reading it, you first learned a bit about
what the Internet is and why it's so popular. Then, you learned
about the variety of services the Internet has to offer-in particular,
the World Wide Web. This lesson discusses the World Wide Web,
pointing out how the World Wide Web fits into the Internet. Furthermore,
the lesson gives you a brief but comprehensive overview of the
major browsers on the market today. The lesson then shows you,
with the help of an analogy, all of the pieces of the World Wide
Web and how they all fit together to get information from one
place to another. Specifically, the lesson discusses how ActiveX
and VBScript fit into the scheme of the Internet and, particularly,
the World Wide Web. In the days that follow, we will discuss VBScript
itself, showing you how to embed script into HTML code and extend
the power and capabilities of Web pages.
Q&A
QDoes any browser that supports HTML also support VBScript?
ANot necessarily, although some day almost all of the popular browsers should. Since VBScript is a new technology, it may take some time before all browsers support it. As VBScript becomes more
popular, browser developers will want to respond to the demands of Web page designers and Web users, and VBScript will become widely supported!
QDoes VBScript replace HTML?
AAbsolutely not. HTML is the foundation upon which Web pages are built. VBScript complements an already existing Web page by making it more powerful and extending its capabilities. You will get
first-hand experience at seeing how VBScript enhances Web pages as you continue reading this book.
QWhy can't VBScript access files on the client system?
AThe ability of VBScript to directly access files on the client computer presents a huge security risk. A Web page could, for example, use VBScript to delete or modify files on a client
computer-a chance nobody would likely want to take. Furthermore, VBScript is intended to work with the ActiveX controls that live inside a Web page. VBScript is not intended to venture beyond the Web page except through these controls. CGI can be used for
that type of interaction on the server, and CGI has much better mechanisms for security.
Workshop
If you haven't already done so, install and become familiar with
as many browsers as you can. Pay particular attention to the Microsoft
Internet Explorer, since this browser will be used for most of
the examples in this book. The more familiar you are with the
browsers available for the Internet, the more you will appreciate
what the World Wide Web provides you and what you can do with
VBScript.
Quiz
Note
Refer to Appendix C, "Answers to Quiz Questions," for the answers to these questions.
What are the most popular services available on the Internet?
What is the name of the language on which Web pages are built?
Is VBScript a part of this language? If not, how does VBScript
run?
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