一、Introduction to Web Services

Web Services can convert your applications into Web-applications.

Web Services are published, found, and used through the Web.

What You Should Already Know

Before you continue, you should have a basic understanding of the following:

HTML
XML

If you want to study these subjects first, find the tutorials on our Home page.

What are Web Services?

Web services are application components
Web services communicate using open protocols
Web services are self-contained and self-describing
Web services can be discovered using UDDI
Web services can be used by other applications
XML is the basis for Web services

How Does it Work?

The basic Web services platform is XML + HTTP.

XML provides a language which can be used between different platforms and programming languages and still express complex messages and functions.

The HTTP protocol is the most used Internet protocol.

Web services platform elements:

SOAP (Simple Object Access Protocol)
UDDI (Universal Description, Discovery and Integration)
WSDL (Web Services Description Language)

We will explain these topics later in the tutorial.

二、Why Web Services?

A few years ago Web services were not fast enough to be interesting.

Interoperability has Highest Priority

When all major platforms could access the Web using Web browsers, different platforms could interact. For these platforms to work together, Web-applications were developed.

Web-applications are simply applications that run on the web. These are built around the Web browser standards and can be used by any browser on any platform.

Web Services take Web-applications to the Next Level

By using Web services, your application can publish its function or message to the rest of the world.

Web services use XML to code and to decode data, and SOAP to transport it (using open protocols).

With Web services, your accounting department's Win 2k server's billing system can connect with your IT supplier's UNIX server.

Web Services have Two Types of Uses

Reusable application-components.

There are things applications need very often. So why make these over and over again?

Web services can offer application-components like: currency conversion, weather reports, or even language translation as services.

Connect existing software.

Web services can help to solve the interoperability problem by giving different applications a way to link their data.

With Web services you can exchange data between different applications and different platforms.

三、Web Services Platform Elements

Web Services have three basic platform elements: SOAP, WSDL and UDDI.

What is SOAP?

SOAP is an XML-based protocol to let applications exchange information over HTTP.

Or more simple: SOAP is a protocol for accessing a Web Service.

SOAP stands for Simple Object Access Protocol
SOAP is a communication protocol
SOAP is a format for sending messages
SOAP is designed to communicate via Internet
SOAP is platform independent
SOAP is language independent
SOAP is based on XML
SOAP is simple and extensible
SOAP allows you to get around firewalls
SOAP is a W3C standard

What is WSDL?

WSDL is an XML-based language for locating and describing Web services.

WSDL stands for Web Services Description Language
WSDL is based on XML
WSDL is used to describe Web services
WSDL is used to locate Web services
WSDL is a W3C standard

What is UDDI?

UDDI is a directory service where companies can register and search for Web services.

UDDI stands for Universal Description, Discovery and Integration
UDDI is a directory for storing information about web services
UDDI is a directory of web service interfaces described by WSDL
UDDI communicates via SOAP
UDDI is built into the Microsoft .NET platform

Read more about UDDI in our WSDL Tutorial.

四、Web Services Example

Any application can have a Web Service component.

Web Services can be created regardless of programming language.

A Web Service Example

In the following example we will use ASP.NET to create a simple Web Service that converts the temperature from Fahrenheit to Celsius, and vice versa:

<%@ WebService Language="VBScript" Class="TempConvert" %>

Imports System
Imports System.Web.Services

Public Class TempConvert :Inherits WebService

<WebMethod()> Public Function FahrenheitToCelsius
(ByVal Fahrenheit As String) As String
dim fahr
fahr=trim(replace(Fahrenheit,",","."))
if fahr="" or IsNumeric(fahr)=false then return "Error"
return ((((fahr) - 32) / 9) * 5)
end function

<WebMethod()> Public Function CelsiusToFahrenheit
(ByVal Celsius As String) As String
dim cel
cel=trim(replace(Celsius,",","."))
if cel="" or IsNumeric(cel)=false then return "Error"
return ((((cel) * 9) / 5) + 32)
end function

end class

This document is saved as an .asmx file. This is the ASP.NET file extension for XML Web Services.

Example Explained

Note: To run this example, you will need a .NET server.

The first line in the example states that this is a Web Service, written in VBScript, and has the class name "TempConvert":

<%@ WebService Language="VBScript" Class="TempConvert" %>

The next lines import the namespace "System.Web.Services" from the .NET framework:

Imports System
Imports System.Web.Services

The next line defines that the "TempConvert" class is a WebService class type:

Public Class TempConvert :Inherits WebService

The next steps are basic VB programming. This application has two functions. One to convert from Fahrenheit to Celsius, and one to convert from Celsius to Fahrenheit.

The only difference from a normal application is that this function is defined as a "WebMethod()".

Use "WebMethod()" to convert the functions in your application into web services:

Then, end the class:

end class

Publish the .asmx file on a server with .NET support, and you will have your first working Web Service.

Look at our example Web Service

ASP.NET Automates the Process

With ASP.NET, you do not have to write your own WSDL and SOAP documents.

If you look closer at our example Web Service, you will see that ASP.NET has automatically created aWSDL and SOAP request.

五、Web Services How to Use

Using the Web Service Example

In the previous page we created a Web service.

The FahrenheitToCelsius() function can be tested here: FahrenheitToCelsius

The CelsiusToFahrenheit() function can be tested here: CelsiusToFahrenheit

These functions will send an XML response like this:

<?xml version="1.0" encoding="utf-8" ?>
<string xmlns="http://tempuri.org/">38</string>

Put the Web Service on Your Web Site

Using a form and the HTTP POST method, you can put the web service on your site, like this:

Fahrenheit to Celsius:

Celsius to Fahrenheit:

How To Do It

Here is the code to add the Web Service to a web page:

<form action='tempconvert.asmx/FahrenheitToCelsius'
method="post" target="_blank">
<table>
<tr>
    <td>Fahrenheit to Celsius:</td>
    <td>
    <input class="frmInput" type="text" size="30" name="Fahrenheit">
    </td>
</tr>
<tr>
    <td></td>
    <td align="right">
     <input type="submit" value="Submit" class="button">
     </td>
</tr>
</table>
</form>

<form action='tempconvert.asmx/CelsiusToFahrenheit'
method="post" target="_blank">
<table>
<tr>
    <td>Celsius to Fahrenheit:</td>
    <td>
    <input class="frmInput" type="text" size="30" name="Celsius">
    </td>
</tr>
<tr>
    <td></td>
    <td align="right">
    <input type="submit" value="Submit" class="button">
    </td>
</tr>
</table>
</form>

Substitute the "tempconvert.asmx" with the address of your web service like:

http://www.example.com/webservices/tempconvert.asmx

六、You Have Learned Web Services, Now What?

Web Services Summary

This tutorial has taught you how to convert your applications into web-applications.

You have learned how to use XML to send messages between applications.

You have also learned how to export a function (create a web service) from your application.

Now You Know Web Services, What's Next?

The next step is to learn about WSDL and SOAP.

WSDL

WSDL is an XML-based language for describing Web services and how to access them.

WSDL describes a web service, along with the message format and protocol details for the web service.

If you want to learn more about WSDL, please visit our WSDL tutorial.

SOAP

SOAP is a simple XML-based protocol that allows applications to exchange information over HTTP.

Or more simply: SOAP is a protocol for accessing a web service.

If you want to learn more about SOAP, please visit our SOAP tutorial.

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