Chapter 12 : Programming XML Web Services

Overview

Microsoft Visual Basic .NET takes advantage of XML Web services technology to multiply the impact of your Microsoft Access databases. In essence, this technology allows you to expose your Access databases over the Web. However, the client application project for an Access database exposed via XML Web services can be either a Microsoft Windows application or a Web application. The Web connection serves strictly as a channel for passing arguments and returning data. XML Web services enable the transformation of Access databases to client/server applications from file server applications. This can occur because the XML Web services technology always works with two applications ”an XML Web service application and a client application. The client application invokes remote procedures in the XML Web service application, and the XML Web service application optionally passes back data to the client application. When XML Web services work with Access databases, it is natural to retrieve data and perform processing in the XML Web service component. This approach can dramatically simplify client programming needs and offer you all the other benefits of .NET development, such as vastly improved scalability.

This chapter offers a practical guide to XML Web services that builds on the basic understanding of the .NET Framework you gained in earlier chapters. The initial section offers a quick overview of the underlying technologies for XML Web services. It is amazing how much the Microsoft Visual Studio .NET IDE dramatically simplifies the use of these technologies so that you can focus on creating your solution. The next section demonstrates how to build a client application for an existing Web service. This section illustrates how to create a Web client and a Windows client. In the process, you will see how a Web reference represents a Web service in a client application and how a proxy variable points at a Web service through a Web reference. The next section demonstrates how to build your own Web service and create client applications for it. In addition to learning how to code your Web service, you will see how to easily test it.

The next to the last section addresses the topic of deploying a Web service from a development computer to a production computer. The approach outlined in this section is particularly appropriate for large to mid- sized organizations that have staging computers for development purposes only. The chapter concludes with a sample application for using an Access database in a Web service. The Web service performs a lookup for a single column value in a row, for a collection of rows, and for a computed value across multiple rows from a join of two tables. You will learn how to isolate these functions via Web methods and put them to use in a client application.