Database Reference
In-Depth Information
Decreased costs. Client/server systems have proven to be powerful enough that organizations
have replaced, at a considerable cost savings, enterprise applications and mainframe databases
with PC applications and databases managed by client/server systems.
Increased scalability. A three-tier client/server system is more scalable than file-server and two-
tier architectures. If an application server or database server becomes a bottleneck, you can
upgrade the appropriate server or add additional processors to share the processing load.
WEB ACCESS TO DATABASES
The Internet, which is a worldwide collection of millions of interconnected computers and computer net-
works that share resources, is used daily by most people and is an essential portal for all organizations. In
particular, people and organizations use the World Wide Web (or the Web), which is a vast collection of
digital documents available on the Internet. Each digital document on the Web is called a Web page, each
computer on which an individual or organization stores Web pages for access on the Internet is called a
Web server, and each computer requesting a Web page from a Web server is called a Web client. A Web
server requires special software to receive and respond to requests for Web pages from Web clients. The
dominant Web server software packages are Apache HTTP Server and IIS. Apache HTTP Server is a free,
open-source package that runs with most operating systems, while Internet Information Services (IIS) is a
Microsoft package that comes with many versions of its operating systems.
Each Web page is assigned an Internet address called a Uniform Resource Locator (URL); the URL iden-
tifies where the Web page is stored
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both the location of the Web server and the name and location of the
Web page on that server. For example, http://www.irs.gov/individuals/index.html is a URL that identifies the
Web server (www.irs.gov), the location path (individuals) on the Web server, and the Web page name
(index.html). The beginning of the URL (http) specifies Hypertext Transfer Protocol (HTTP), which is
the data communication method used by Web clients and Web servers to exchange data on the Internet.
You use a computer program called a Web browser to retrieve a Web page from a Web client; popular
Web browsers include Microsoft Internet Explorer, Mozilla Firefox, Safari, Google Chrome, and Opera. As
shown in Figure 9-7, a user enters the Web page
—
s URL in a Web browser on a Web client and then sends the
request for the Web page over the Internet using HTTP and Transmission Control Protocol/Internet Protocol
(TCP/IP), which is the standard protocol for all communication on the Internet. The request for the Web
page arrives at the Web server designated in the transmitted URL, and the Web server locates the requested
Web page on a disk connected to the Web server and retrieves the Web page. The Web server then responds
to the Web client by transmitting the Web page over the Internet using HTTP and TCP/IP, and the Web
browser displays the Web page on the user
'
s screen. Note that Web clients on an intranet bypass the Internet
and directly access internal company Web pages through the organization
'
'
s Web server.
