• Web services are services provided over the web using standard technologies such as XML, a W3C standard.
  • Any application on any platform can consume a web service as long as it is able to understand XML.
  • XML is text based, thus it is quick and easy to download and even easier to use.
  • To consume an ASP.NET web service, look for an .asmx file.
  • An example of a web service is http://www.webservicex.net/ConvertTemperature.asmx.
  • There are 3 methods used to communicate with a web service: HTTP-GET, HTTP-POST, and SOAP.

  • In HTTP GET and POST, the response body is an XML.  Below is an example response from the ConvertTemperature web service mentioned above, converting 21.5 degrees Celcius to degrees Farenheit.

    <?xml version=“1.0” encoding=“UTF-8”?> <double xmlns=“http://www.webserviceX.NET/”>70.7</double>

     

 

  • SOAP (Simple Object Access Protocol) is basically a well-formed XML created just for the purpose of sending requests and receiving responses to and from the web service.

  • A SOAP request is wrapped in an HTTP-POST.  The example below is the SOAP request sent to the ConvertTemperature web service, separated into a request header and request body:

    POST /ConvertTemperature.asmx HTTP/1.1 Host: www.webservicex.net Content-Type: text/xml; charset=utf-8 Content-Length: [length] SOAPAction: “http://www.webserviceX.NET/ConvertTemp”

     

    <?xml version=“1.0” encoding=“utf-8”?> <soap:Envelope xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance” xmlns:xsd=“http://www.w3.org/2001/XMLSchema” xmlns:soap=“http://schemas.xmlsoap.org/soap/envelope/”> <soap:Body> <ConvertTemp xmlns=“http://www.webserviceX.NET/”> <Temperature>21.5</Temperature> <FromUnit>degreeCelsius</FromUnit> <ToUnit>degreeFahrenheit</ToUnit> </ConvertTemp> </soap:Body> </soap:Envelope>

     

 

  • The corresponding SOAP response is below (response header not shown):

    <?xml version=“1.0” encoding=“utf-8”?> <soap:Envelope xmlns:xsi=“http://www.w3.org/2001/XMLSchema-instance” xmlns:xsd=“http://www.w3.org/2001/XMLSchema” xmlns:soap=“http://schemas.xmlsoap.org/soap/envelope/”> <soap:Body> <ConvertTempResponse xmlns=“http://www.webserviceX.NET/”> <ConvertTempResult>70.7</ConvertTempResult> </ConvertTempResponse> </soap:Body> </soap:Envelope>

     

 

  • In the SOAP request and response body, you need to have at the minimum the SOAP tags **** and **<Body>**.  You can also have the optional SOAP tag **<Header>**.  Inside the **<Body>** SOAP tag contains other tags that are specific to the web service.

 

In my next post, I will talk about what is required to create a web service in ASP.NET.