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Q6-3 How Does the Cloud Work?

Instructions 253
and Data

Commerce Other
Server Applications
Commerce
Other
..... Other
Server
Commerce
Web Browsers Application Applications
Server
Commerce
..... Other
Web Browsers Application Applications
Web Server
.....
Server
Web Browsers Application Applications
(Apache, IIS)
Web Server
Web Browsers Application ..... DBMS
Web Browsers (Apache, IIS) DB
Web Server
(Apache, IIS)
Web Server
html
via http (Apache, IIS)
User Computers Web Server Computers DBMS Computer
Figure 6-10 (User Tier) (Server Tier) (Database Tier)
Three-Tier Architecture
When you enter www.zulily.com in your browser, the browser sends a request that travels
over the Internet to a computer in the server tier at the zulily site. In response to your request, a
server-tier computer sends back a Web page, which is a document coded in, usually, html (and, as
discussed in Chapter 4, probably includes CSS, JavaScript, and other data).
Web servers are programs that run on a server-tier computer and manage traffic by sending
and receiving Web pages to and from clients. A commerce server is an application program that
runs on a server-tier computer. Typical commerce server functions are to obtain product data from a
database, manage the items in a shopping cart, and coordinate the checkout process. When a request
comes to the server, the Web server examines it and sends it to the proper program for processing.
Thus, the Web server passes e-commerce traffic to the commerce server. It passes requests for other
applications to those applications. In Figure 6-10, the server-tier computers are running a Web server
program, a commerce server application, and other applications having an unspecified purpose.
Watch the Three Tiers in Action!

Suppose the user of the Web page in Figure 6-9 clicks on shoes and then selects a particular shoe,
say, the Darkish Gray Dorine Mary Jane shoe. When the user clicks on that shoe, the commerce
server requests that shoe’s data from the DBMS, which reads it from the database and then returns
the data (including pictures) to the commerce server. That server then formats the Web page with
the data and sends the html version of that page to the user’s computer. The result is the page
shown in Figure 6-11.

Service-Oriented Architecture (SOA)

The cloud would be impossible without a design philosophy called the service-oriented archi-
tecture (SOA). According to this philosophy, all interactions among computing devices are
defined as services in a formal, standardized way. This philosophy enables all the pieces of the
cloud to fit together, as you will see. However, understanding SOA (pronounced SO-ah) in depth
requires you to learn more computer science than you need as a business professional. So, the best
way for you to understand SOA is via a business analogy.

A SOA Analogy

Figure 6-12 shows an arrangement of departments at a hypothetical online bicycle part
retailer named Best Bikes. The Sales Department receives order requests and follows a process
to have them approved for shipping. On request, the Credit Department verifies customer credit