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Web Services Tutorial
Web Services can convert your application into a Web-application, which can publish its function or message to the rest of the world.
The basic Web Services platform is XML + HTTP. 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:
What are 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:
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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 simple 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. |
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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.
WSDL is an XML-based language for locating and describing Web services.
What is UDDI? UDDI is a directory service where companies can register and search for Web services.
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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 (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 (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. |
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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: (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 (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 Then, end the class: end class |