.NET/ASP.NET/C#/VB.NET PDF Document SDK

Web services can be used to implement service-oriented architectures, a popular application integration strategy where the interacting software components and services are loosely coupled in a distributed environment. The benefits of such integration include allowing offering services as independent entities that can be used and reused from different systems within an organization or even the entire world. Consuming web services thus is a great way to expand the functionality of your application. A web service is a set of functionality that is offered through a platform-independent interface. Applications can explore the pieces of functionality offered by a web service by examining its Web Services Description Language (WSDL) signature. This WSDL definition uses XML to describe the signature of each operation by declaring the data types of the parameters and optional return values. Communicating with a web service occurs via the Simple Object Access Protocol (SOAP), which encodes service invocations and return values in an XML envelope over HTTP. Because web services are invoked over HTTP, they can be used by any application with Internet connectivity. Communicating with web services is usually performed via so-called proxy classes. A proxy performs all the grunge work involved in calling the service and deciphering the results, freeing you from a lot work. A typical workflow when calling a web service is the following:

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Elapsed Time (Milliseconds)

1. The client instantiates the proxy and calls the desired operation on it. 2. The proxy creates a SOAP XML request and sends it to the web service via HTTP. 3. The web service receives the request and performs the requested operation. 4. The web service packages the return value from the operation (or any exception that occurred within) into a SOAP XML response and returns it to the proxy via HTTP. 5. The proxy deserializes the response into a .NET data type and returns it to the calling class.

Executes a given XQuery expression on the contained XML and returns the result as an instance of XML type. Executes a given XQuery expression on the contained XML and converts the result to a given SQL type (such as int, varchar, etc.) The XQuery expression must return a scalar value. Executes a given XQuery expression on the contained XML and returns 1 (representing true) if the query finds at least one matching XML node. Otherwise the method returns 0 (representing false). Updates the contained XML according to the given XML Data Manipulation Language (XML DML) expression. Executes the given XQuery expression on the contained XML and returns the resulting nodes as a rowset. This is useful for shredding an XML document in to relational tables.

96,982 50,386 20,046 10,219 2,882 1,753 1,008 951 1,109

Many great web services are available on the Internet. For instance, Microsoft s TerraService is a free web service at http://terraservice.net that enables you to integrate USGS images and data into your applications. Also, http://webservicex.net is another great source for web services; for instance, its WeatherForecast web service can supply weather information for any given U.S. location. Calling these and other web services in your .NET applications is quite painless using F# web references. All web services are called via generated proxy code. The easiest way to generate this code is by adding a web reference to Visual Studio, which automatically generates a .NET proxy class for the given web service. Figure 14-5 shows the available operations for the web service from http://webservicex.net/WeatherForecast.asmx.

-51.95 39.78 50.98 28.20 60.83 57.50 94.35 116.61

As you study these methods, you see a common theme: They all rely on XQuery expressions. XQuery is a relatively recent language created by the World Wide Web Consortium (W3C) to provide an SQL-like query language for XML data. Therefore, it makes an ideal

You can also generate code using the .NET command-line tool wsdl.exe. Here is an example where you generate C# code for TerraService and WeatherForecast and compile it explicitly: C:\fsharp> wsdl /namespace:WebReferences http://webservicex.net/WeatherForecast.asmx Microsoft (R) Web Services Description Language Utility Writing file 'C:\fsharp\WeatherForecast.cs'. C:\fsharp> csc /target:library WeatherForecast.cs C:\fsharp> wsdl /namespace:WebReferences http://terraservice.net/terraservice.asmx Microsoft (R) Web Services Description Language Utility Writing file 'C:\fsharp\TerraService.cs'. C:\fsharp> csc /target:library TerraService.cs C:\fsharp> dir *.dll ... 04/09/2007 00:18 04/09/2007 00:18

As you can see, the elapsed time decreases dramatically as the fetch size increases. The optimal elapsed time corresponding to a fetch size of 10,000 in our run had an elapsed time that was only 0.98% of the elapsed time corresponding to the default fetch size of 10. As is expected, though, after a certain point, diminishing returns set in (in this case because of the increase in memory required in the client-side cache that stores these prefetched results), and eventually the elapsed time starts showing an upward trend. Next, we plot the number of logical I/Os for each fetch size, as shown in Figure 7-2.

6000 5000 4000

Note You can also use wsdl.exe to generate F# code by adding a command-line option that gives an explicit reference to the F# CodeDom dynamic code generator. For example, an option such as /language: "Microsoft.FSharp.Compiler.CodeDom.FSharpCodeProvider, Microsoft.FSharp.Compiler. CodeDom, Version=1.9.2.9, Culture=neutral, PublicKeyToken=a19089b1c74d0809" can be used. Note the similarity with the CodeDom reference used in the web.config file in Listing 14-2. The generated file can then be compiled as normal, though the authors have found that small adjustments sometimes need to be made to the generated code.