As shown in Figure 3-7, proper implementation of the shopping cart application requires integration of several different electronic business components. First, it is integrated with a session management component, which keeps track of a customer’s shopping session. Second, it is integrated with the product catalog application, which generates a display of products sold by the storefront and allows the customer to browse the products; the customer can select a product from the catalog and place it in the shopping cart. Third, it is integrated with—acts as an input to—the payment gateway, which comes into play at the end of the shopping session. Fourth, it is integrated with back-end databases such as product inventory for automatically verifying and updating stock quantities, customer information for tracking customers’ buying preferences, and so on.

Figure 3-7. Shopping cart implementation - technology perspective

Since the early days of electronic retail shopping, many types of shopping carts have been introduced. Some shopping carts were made publicly available along with the source code, whereas some were sold as commercial third-party applications. Of the plethora of shopping carts, many failed because of improper implementation, which eventually led to security vulnerabilities.

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Introduction

Retail shopping has evolved dramatically over the years. In the earlier days of shopping, a shopkeeper would sit behind a counter and respond to requests from a customer, selecting a product from the shelf and handing it to the customer for her consideration. The customer would then indicate whether she was interested in buying it. If so, the product would be set aside, the shopkeeper would respond to the customer’s next request, and after the customer was satisfied with all the items set aside, the shopkeeper would prepare the final bill and accept payment. If the customer didn’t like a product, the shopkeeper would naturally reshelve it.

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CSS was designed to work with HTML. To take advantage of CSS, you need to know some HTML. As stated in the Preface, we assume most readers have had some exposure to HTML. However, to ensure we all talk about the same thing, we now review the basics of HTML.

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A markup language is a method of indicating within a document the roles that the document’s pieces are to play. Its focus is on the structure of a document rather than its appearance. For example, you can indicate that one piece of text is a paragraph, another is a top-level heading, and another is a lower-level heading. You indicate these by placing codes, called tags, into the document. HTML has around 30 commonly used tags, which are reviewed later in this chapter. You could, for example, use a tag that says, in effect, “Make this piece of text a heading.”

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Cascading Style Sheets (CSS) represent a major breakthrough in how Web-page designers work by expanding their ability to control the appearance of Web pages, which are the documents that people publish on the Web.

For the first few years after the World Wide Web (the Web) was created in 1990, people who wanted to put pages on the Web had little control over what those pages looked like. In the beginning, authors could only specify structural aspects of their pages (for example, that some piece of text would be a heading or some other piece would be straight text). Also, there were ways to make text bold or italic, among a few other effects, but that’s where their control ended.

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That’s not a typoPHP lets you create variable variables. A variable variable is one that holds the name of a variable. Here’s how it works: you create a variable named, say, $apples:

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If php is in your path, you can run this from the command line like so (where % is a generic, cross-platform command-line prompt, and this example assumes you’re in the same directory as echo.php):

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PHP files are most often mixtures of HTML and PHP scripts. Putting HTML and PHP scripts into the same document is no problem because you put your PHP statements inside a script bounded by <?php and ?>, which means the server can pick them out easily.

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Here’s where all the action startscreating your first PHP scripts. With PHP, which will be run on the web server, you can make all kinds of things happen that couldn’t happen before. You can have your PHP retrieve data from databases, check someone’s password, print out customized greeting text, use cookies, write a guest book, create interactive games, calculate sales tax, or even build your own shopping cart or chat room web applications. And all these things can run by themselves, 24 hours a day, even while you’re peacefully sleeping in bed.

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