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Chapter 6 The Cloud
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Before we leave addressing, you need to know one more term. A URL (Uniform Resource
Locator) is an address on the Internet. Commonly, it consists of a protocol (such as http:// or
ftp://) followed by a domain name or public IP address. A URL is actually quite a bit more compli-
cated than this description, but that detailed knowledge is beyond the scope of this text, so we’ll
hurry along. The preferred pronunciation of URL is to say the letters U, R, L.

Processing on a Web Server

At this point, you know basic networking terms and have a high-level view of how the Internet works.
To understand the value of the cloud, and how it works and how your organization can use it, you
need to know a bit about the processing that occurs on a Web server. For this discussion, we will use
the example of a Web storefront, which is a server on the Web from which you can buy products.
Suppose you want to buy an item from zulily, a private buyer’s site that sells clothing. To do so,
you go to www.zulily.com and navigate to the product(s) you want to buy (see Figure 6-9). When
you find something you want, you add it to your shopping cart and keep shopping. At some point,
you check out by supplying credit card data. But what happens when your order data arrives at
the server?

Three-Tier Architecture
Almost all Web applications use the three-tier architecture, which is a design of user com-
puters and servers that consists of three categories, or tiers, as shown in Figure 6-10. The user
tier consists of computers, phones, and other mobile devices that have browsers that request
and process Web pages. The server tier consists of computers that run Web servers and process
application programs. The database tier consists of computers that run a DBMS that processes
requests to retrieve and store data. Figure 6-10 shows only one computer at the database tier.
Some sites have multicomputer database tiers as well.

Figure 6-9
Sample of Commerce Server
Pages; Product Offer Pages
Source: Courtesy of Zuilly Inc.
Used by permission.