A Web Service is programmable application logic accessible via standard Web protocols. One of these Web protocols is the Simple Object Access Protocol (SOAP). SOAP is a W3C submitted note that uses standards based technologies (XML for data description and HTTP for transport) to encode and transmit application data.

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)

Web Services are a very general model for building applications and can be implemented for any operation system that supports communication over the Internet. Web Services use the best of component-based development and the Web. Component-base object models like Distributed Component Object Model (DCOM), Remote Method Invocation (RMI), and Internet Inter-Orb Protocol (IIOP) have been around for some time. Unfortunately all these models depend on an object-model-specific protocol. Web Services extend these models a bit further to communicate with the Simple Object Access Protocol (SOAP) and Extensible Markup Language (XML) to eradicate the object-model-specific protocol.

Creating a Web Service


We are going to use C# to create a Web Service called "SecurityWebService." A Web Service file will have an .ASMX file extension. (as opposed to an .ASPX file extension of a ASP.NET file). The first line of the file will look like

    <%@ WebService Language="C#" class="SecurityWebService" %>

This line will instruct the compiler to run on Web Service mode and the name of the C# class. We also need to access the Web Service namespace. It is also a good practice to add a reference to the System namespace.

    using System;
    using System.Web.Services;

The SecurityWebService class should inherit the functionality of the Web Services class. Therefore, we put the following line of code:

    public class SecurityWebService : WebService

Now we can use our object-oriented programming skills to build a class. C# classes are very similar to C++ or Java classes. It will be a walk in the park to create a C# class for anyone with either language-coding skills.

Dot-net Web Services are intelligent enough to cast basic data types. Therefore, if we return "int," "float," or "string" data types, it can convert them to standard XML output. Unfortunately, in most cases we need get a collection of data regarding a single entity. Let's take an example.

Our SecurityWebService stock quotes service requires the user to enter a company code, and it will deliver the full company name and the current stock price. Therefore, we have three pieces of information for a single company:

   1. Company code (data type - string)
   2. Company name (data type - string)
   3. Price (data type - Double)

We need to extract all this data when we are referring to a single stock quote. There are several ways of doing this. The best way could be to bundle them in an enumerated data type. We can use "structs" in C# to do this, which is very similar to C++ structs.

    public struct SecurityInfo
        {
            public string Code;
            public string CompanyName;
            public double Price;
        }

Now we have all the building blocks to create our Web Service. Therefore, our code will look like.


<%@ WebService Language="C#" class="SecurityWebService" %>

using System;
using System.Web.Services;

public struct SecurityInfo
{
    public string Code;
    public string CompanyName;
    public double Price;
}

public class SecurityWebService : WebService
{
    private SecurityInfo Security;
   
    public SecurityWebService()
    {
        Security.Code = "";
        Security.CompanyName = "";
        Security.Price = 0;
    }

    private void AssignValues(string Code)
    {
        // This is where you use your business components.
        // Method calls on Business components are used to populate the data.
        // For demonstration purposes, I will add a string to the Code and
        //        use a random number generator to create the price feed.
                   
        Security.Code = Code;
        Security.CompanyName = Code + " Pty Ltd";
        Random RandomNumber = new System.Random();
        Security.Price = double.Parse(new System.Random(RandomNumber.Next(1,10)).NextDouble().ToString("##.##"));
    }


    [WebMethod(Description="This method call will get the company name and the price for a given security code.",EnableSession=false)]
    public SecurityInfo GetSecurityInfo(string Code)
    {
        AssignValues(Code);
        SecurityInfo SecurityDetails = new SecurityInfo();
        SecurityDetails.Code = Security.Code;
        SecurityDetails.CompanyName = Security.CompanyName;
        SecurityDetails.Price = Security.Price;
        return     SecurityDetails;
    }

}

Remember, this Web Service can be accessed through HTTP for any use. We may be referring to sensitive business data in the code and wouldn't want it to fall into the wrong hands. The solution is to protect the business logic function and only have access to the presentation functions. This is achieved by using the keyword "[Web Method]" in C#. Let's look at the function headers of our code.

    [WebMethod(Description="This......",EnableSession=false)]
    public SecurityInfo GetSecurityInfo(string Code)

This function is exposed to the public. The "description" tag can be used to describe the Web Service functionality. Since we will not be storing any session data, we will disable the session state.

    private void AssignValues(string Code)

This is a business logic function that should not be publicly available. We do not want our sensitive business information publicly available on the Web. (Note:- Even if you change the "private" keyword to "public," it will still not be publicly available. You guessed it, the keyword "[Web Method]" is not used.)

We can use the business logic in this function to get the newest stock price quote. For the purpose of this article I have added some text to the company code to create the company name. The price value is generated using a random number generator.

We may save this file as "SampleService.asmx" under an Internet Information Service (IIS)-controlled directory. I have saved it under a virtual directory called "/work/aspx." I'll bring it up on a Web browser.