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If you are like most developers, you probably know of a couple of areas where you can use Web services, but maybe you are still asking yourself, "What can I really do with XML Web services?"
The easiest, or most obvious, use of Web services is to export information that you could conveniently incorporate into applications, like stock quotes, weather forecasts, sports scores, business information, and so on. It is easy to imagine applications that could be built to analyze and aggregate the information you care about and present it to you in a variety of ways. For example, you might have a Microsoft Excel spreadsheet that summarizes your company's financial picture—stocks, bank accounts, loans, and so on. If this information is available through XML Web services, Excel can update it continuously. It will also be possible for your colleagues to easily retrieve and access this information—no matter where they are located in the organization.
Some of this information will be accessible to everyone, and some might require a subscription to the service. Most of this information may already be available on the Web, but XML Web services will make programmatic access to this information easier and more reliable.
The ability to programmatically access the information makes it possible to expose existing application functionality as Web services. This allows developers to build new, more powerful applications that use XML Web services as building blocks. For example, a developer might develop an authentication Web service that automatically checks the username and password from the company's Active Directory. This Web service can then be used from the time reporting application we will present in Chapter 9 to authenticate users.
An other example of the strength of Web services is when a developer exposes an old legacy system, like a financial system, so developers can easily retrieve information about specific orders or billing information. This Web service can be used to do a report for the time reporting application in Chapter 9, in which we compare the reported time from the user of the application, with the time billed to the customer.
The latter example shows that old legacy systems may be exposed with Web services, orders can be read and placed in the legacy system directly, and the different products that were ordered reserved from the stock. From the legacy system it is also possible to retrieve discounts for the customer and include them in the order. Many companies today expose their old legacy systems via Web services, thereby making it easier to access business information in a controlled way for developers.
In the section "Using SOAP" later in this chapter, you will study some examples of Web services, in particular an example of using Web services to collect error information. In the section "WSE and Security," we will show you how to encrypt the content of your Web services.
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