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Before moving on to more complicated WSDL examples, let's examine another relatively simple one. Example 6-3 provides a WSDL file for the XMethods eBay Price Watcher Service. The service takes an existing eBay auction ID, and returns the value of the current bid.

Example 6-3: eBayWatcherService.wsdl (reprinted with permission of XMethods, Inc.)

<?xml version="1.0"?>
<definitions name="eBayWatcherService" 
   targetNamespace=
      "http://www.xmethods.net/sd/eBayWatcherService.wsdl"
   xmlns:tns="http://www.xmethods.net/sd/eBayWatcherService.wsdl"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
   xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
   xmlns="http://schemas.xmlsoap.org/wsdl/">
  
   <message name="getCurrentPriceRequest">
      <part name="auction_id" type = "xsd:string"/>
   </message>
   <message name="getCurrentPriceResponse">
      <part name="return" type = "xsd:float"/>
   </message>
  
   <portType name="eBayWatcherPortType">
      <operation name="getCurrentPrice">
         <input 
            message="tns:getCurrentPriceRequest"
            name="getCurrentPrice"/>
         <output 
            message="tns:getCurrentPriceResponse"
            name="getCurrentPriceResponse"/>
      </operation>
   </portType>
  
   <binding name="eBayWatcherBinding" type="tns:eBayWatcherPortType">
      <soap:binding 
         style="rpc"
         transport="http://schemas.xmlsoap.org/soap/http"/>
      <operation name="getCurrentPrice">
         <soap:operation soapAction=""/>
         <input name="getCurrentPrice">
            <soap:body 
               use="encoded"
               namespace="urn:xmethods-EbayWatcher"
               encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
         </input>
         <output name="getCurrentPriceResponse">
            <soap:body
               use="encoded"
               namespace="urn:xmethods-EbayWatcher"
               encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
         </output>
      </operation>
   </binding>
  
   <service name="eBayWatcherService">
      <documentation>
         Checks current high bid for an eBay auction
      </documentation>
      <port name="eBayWatcherPort" binding="tns:eBayWatcherBinding">
         <soap:address 
          location=
	  "http://services.xmethods.net:80/soap/servlet/rpcrouter"/>
      </port>
   </service>
</definitions>

Here is an overview of the main WSDL elements:

messages

Two messages are defined: getCurrentPriceRequest and getCurrentPriceResponse. The request message contains a single string parameter; the response message contains a single float parameter.

portType

A single operation, getCurrentPrice, is defined. Again, we see the request/response operation pattern.

binding

The binding element specifies HTTP SOAP as the transport. The soapAction attribute is left as an empty string ("").

service

This element specifies that the service is available at http://services.xmethods.net/soap/servlet/rpcrouter.

To access the eBay watcher service, you can use any of the WSDL invocation tools defined earlier. For example, the following call to GLUE:

invoke http://www.xmethods.net/sd/2001/EBayWatcherService.wsdl
    getCurrentPrice 1271062297

retrieves the current bid price for a Handspring Visor Deluxe:

result = 103.5

TIP:  The XMethods web site (http://www.xmethods.net/) provides dozens of sample SOAP and .NET services. Nearly all of these services include WSDL files and therefore provide an excellent opportunity for learning WSDL in detail. As you browse the XMethods directory, try interfacing with the specified services via any of the WSDL invocation tools described here. Quite likely, you will be amazed at how easy it is to integrate and invoke new services.

WSDL Invocation Tools, Part I - Page 4
Web Services Essentials
WSDL Invocation Tools, Part II - Page 6