16.1. The Overall Design To see how various technologies work together you will actually build two independent applications (a desktop application web services client and an ASP.NET application) tied together by a backend database. Specifically, you'll create a desktop application that obtains data from Amazon's web service and stores it in a table in a SQL Server database, and then you'll display that data in your ASP.NET application.[1] [1] Content on Amazon is copyrighted and can't be used without written permission. Such permission was graciously provided for this book and for use on my web site, http://www.LibertyAssociates.com.
The SQL Server database is very simple. It is named AmazonSalesRanks and consists of a single table, BookInfo, as shown in Figure 16-1. Figure 16-1. Designing the BookInfo table 
 | All the fields in this table are allowed to be null because you can't control what information may or may not be available from Amazon at any particular moment. To make this design more robust, you might consider making the ISBN a primary key and rejecting any data that returns without an ISBN. This is left, as they say, as an exercise for the reader. |
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The Screen-Scraper Application In previous editions of this book, we first implemented the desktop application as a screen-scraper that downloaded data from Amazon.com. At that time, I pointed out that screen-scraping works great as long as Amazon always lists the rank in exactly this way, but if it doesn't, the parsing will fail. Each time Amazon changes its pages, you must upgrade this program. In addition, I pointed out that the data on Amazon's pages is copyrighted, and so there are serious legal and ethical issues about scraping Amazon's pages. Since the publication of the previous edition, Amazon has instituted security on its site that blocks simple screen-scraping applications. Since it also provides extensive support for web services, this chapter will implement the application using those web services, and we'll cover screen-scraping in Chapter 21, where we'll (legally and ethically) scrape screens from my own web site. |
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