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Web Services can make your applications Web applications.
Web Services are published, found and used through the Web.
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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.
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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
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How Does it Work?
The basic Web services platform is XML + HTTP.
The HTTP protocol is the most used Internet protocol.
XML provides a language which can be used between different platforms and programming languages and still express complex messages and functions.
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
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The Future of Web services
Don't expect too much, too soon.
The Web Services platform is a simple, interoperable, messaging framework. It still misses many important features like security and routing. But, these pieces will come once SOAP becomes more advanced.
Hopefully, Web services can make it much easier for applications to communicate
Why Web Services?
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A few years ago Web services were not fast enough to be interesting.
Thanks to the major IT development the last few years, most people and companies have broadband connection and use the web more and more.
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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 simple applications run on the web. These are built around the Web browser standards and can mostly be used by any browser on any platform.
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Web services take Web applications to the next level.
Using Web services your application can publish its function or message to the rest of the world.
Web services uses XML to code and decode your data and SOAP to transport it using open protocols.
With Web services your accounting departments Win 2k servers billing system can connect with your IT suppliers UNIX server.
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Web services have two types of uses.
Reusable application components
There are things different applications needs 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.
Ideally, there will only be one type of each application component, and anyone can use it in their application.
Connect existing software
Web services help solve the interoperability problem by giving different applications a way to link their data.
Using Web services you can exchange data between different applications and different platforms.
Web Services Platform Elements
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Web Services have three basic platform elements.
These are called SOAP, WSDL and UDDI.
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What is SOAP?
The basic Web services platform is XML plus HTTP.
• SOAP stands for Simple Object Access Protocol
• SOAP is a communication protocol
• SOAP is for communication between applications
• 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 will be developed as a W3C standard
Read more about SOAP on our Home page.
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What is WSDL?
WSDL is an XML-based language for describing Web services and how to access them.
• WSDL stands for Web Services Description Language
• WSDL is written in XML
• WSDL is an XML document
• WSDL is used to describe Web services
• WSDL is also used to locate Web services
• WSDL is not yet a W3C standard
Read more about WSDL on our Home page.
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What is UDDI?
UDDI is a directory service where businesses 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 on our Home page.
Web Service Example
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Any application can have a Web Service component.
Web Services can be created regardless of programming language.
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An example ASP.NET Web Service
In this example we use ASP.NET to create a simple Web Service.
<%@ WebService Language="VB" Class="TempConvert" %>
Imports System
Imports System.Web.Services
Public Class TempConvert :Inherits WebService
(ByVal Fahrenheit As Int16) As Int16
Dim celsius As Int16
celsius = ((((Fahrenheit) - 32) / 9) * 5)
Return celsius
End Function
(ByVal Celsius As Int16) As Int16
Dim fahrenheit As Int16
fahrenheit = ((((Celsius) * 9) / 5) + 32)
Return fahrenheit
End Function
End Class
This document is a .asmx file. This is the ASP.NET file extension for XML Web Services.
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To run this example you will need a .NET server.
The first line in this document that it is a Web Service, written in VB and the class name is "TempConvert":
<%@ WebService Language="VB" Class="TempConvert" %>
The next lines imports 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 WebSerivce class type:
Public Class TempConvert :Inherits WebService
The next step is 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 mark the functions in your application that you would like to make into web services.
(ByVal Fahrenheit As Int16) As Int16
Dim celsius As Int16
celsius = ((((Fahrenheit) - 32) / 9) * 5)
Return celsius
End Function
(ByVal Celsius As Int16) As Int16
Dim fahrenheit As Int16
fahrenheit = ((((Celsius) * 9) / 5) + 32)
Return fahrenheit
End Function
The last thing to do is to end the function and the class:
End Function
End Class
If you save this as an .asmx file and publish it on a server with .NET support, you should have your first working Web Service. Like our example Web Service
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ASP.NET automates the process
With ASP.NET you do not have to write your own WSDL and SOAP documents.
If you look closer on our example Web Service. You will see that the ASP.NET has automatically created a WSDL and SOAP request.
Web Service Use
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Using our example ASP.NET Web Service
In the previous example we created an example Web Service.
The Fahrenheit to Celsius function can be tested here: FahrenheitToCelsius.
The Celsius to Fahrenheit function can be tested here: CelsiusToFahrenheit.
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These functions will send you a XML reply.
These test use HTTP POST and will send a XML response like this:
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Use a form to access a Web Service.
Using a form and HTTP POST, you can put our web service on your site, like this:
Fahrenheit to Celsius:
Celsius to Fahrenheit:
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You can put our Web Service on your site.
Here is the code to put our Web Service on your site:
method="POST">
| Fahrenheit to Celsius: | size="30" name="Fahrenheit"> |
| value="Submit" class="button"> |
method="POST">
| Celsius to Fahrenheit: | size="30" name="Celsius"> |
| value="Submit" class="button"> |
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