Web Services in Microsoft.Net

What is Service-Oriented Architecture?

service-oriented architecture is collection of many services in the network. These services communicate with each other and the communications involves data exchange & even service coordination. Earlier SOA was based on the DCOM or Object Request Brokers (ORBs).

Broadly SOA can be classified into two terms: Services and Connections

Services:

A service is a function or some processing logic or business processing that is well-defined, self-contained, and does not depend on the context or state of other services.

Connections:

Connections means the link connecting these self-contained distributed services with each other, it enable client to Services communications. In case of Web services SOAP over HTTP is used to communicate the between services.

Why SOA?

SOA architecture enables seamless Enterprise Information Integration.

Here are some of the Benefits of the Service Oriented Architecture:

Due to its platform independence, it allows companies to use the software and hardware of their choice .

SOA enables incremental development, deployment, and maintenance.

Companies can use the existing software (investments) and use SOA to build applications without replacing existing applications

The training costs are low, so the available labor pool can be used for running the applications

What is a Web Service

The next generation of distributed computing has arrived. A Web service is a unit of managed code that can be remotely invoked using HTTP, that is, it can be activated using HTTP requests.

Historically speaking, remote access to binary units required platform-specific and sometimes language-specific protocols. For example, DCOM clients access remote COM types using tightly coupled RPC calls. CORBA requires the use of tightly coupled protocol referred to as Internet Inter-ORB Protocol (IIOP), to activate remote types. Enterprise JavaBeans (EJBs) requires a Remote Method Invocation (RMI) Protocol and by and large a specific language (Java). Thus each of these remote invocation architectures needs proprietary protocols, which typically require a tight connection to the remote source.

One can access Web services using nothing but HTTP. Of all the protocols in existence today, HTTP is the one specific wire protocol that all platforms tend to agree on. Thus , using Web services, a Web service developer can use any language he wish and a Web service consumer can use standard HTTP to invoke methods a Web service provides. The bottom line is that we have true language and platform integration . Simple Object Access Protocol (SOAP) and XML are also two key pieces of the Web services architecture.

Web services constitute a distributed computer architecture made up of many different computers trying to communicate over the network to form one system. They consist of a set of standards that allow developers to implement distributed applications – using radically different tools provided by many different vendors – to create applications that use a combination of software modules called from systems in disparate departments or from other companies.

A Web service contains some number of classes, interfaces, enumerations and structures that provide black box functionality to remote clients. Web services typically define business objects that execute a unit of work (e.g., perform a calculation, read a data source, etc.) for the consumer and wait for the next request. Web service consumer does not necessarily need to be a browser-based client. Console-baed and Windows Forms-based clients can consume a Web service. In each case, the client indirectly interacts with the Web service through an intervening proxy. The proxy looks and feels like the real remote type and exposes the same set of methods. Under the hood, the proxy code really forwards the request to the Web service using standard HTTP or optionally SOAP messages.

Web Service Standards

Web services are registered and announced using the following services and protocols. Many of these and other standards are being worked out by the UDDI project, a group of industry leaders that is spearheading the early creation and design efforts.

Universal Description, Discovery, and Integration (UDDI) is a protocol for describing available Web services components. This standard allows businesses to register with an Internet directory that will help them advertise their services, so companies can find one another and conduct transactions over the Web. This registration and lookup task is done using XML and HTTP(S)-based mechanisms.

Simple Object Access Protocol (SOAP) is a protocol for initiating conversations with a UDDI Service. SOAP makes object access simple by allowing applications to invoke object methods or functions, residing on remote servers. A SOAP application creates a request block in XML, supplying the data needed by the remote method as well as the location of the remote object itself.

Web Service Description Language (WSDL), the proposed standard for how a Web service is described, is an XML-based service IDL (Interface Definitition Language) that defines the service interface and its implementation characteristics. WSDL is referenced by UDDI entries and describes the SOAP messages that define a particular Web service.

Why Web Services?

Here are the benefits of using Web Services:

Exposing the function on to network: A Web service is a unit of managed code that can be remotely invoked using HTTP, that is, it can be activated using HTTP requests. So, Web Services allows you to expose the functionality of your existing code over the network. Once it is exposed on the network, other application can use the functionality of your program.

connecting Different Applications: Web Services allows different applications to talk to each other and share data and services among themselves. Other applications can also use the services of the web services. For example VB or .NET application can talk to java web services and vice versa. So, Web services is used to make the application platform and technology independent.

Standardized Protocol: Web Services uses standardized industry standard protocol for the communication. All the four layers (Service Transport, XML Messaging, Service Description and Service Discovery layers) uses the well defined protocol in the Web Services protocol stack. This standardization of protocol stack gives the business many advantages like wide range of choices, reduction in the cost due to competition and increase in the quality.

Low Cost of communication: Web Services uses SOAP over HTTP protocol for the communication, so you can use your existing low cost internet for implementing Web Services. This solution is much less costly compared to proprietary solutions like EDI/B2B.

Support for Other communication means: Beside SOAP over HTTP, Web Services can also be implemented on other reliable transport mechanisms. So, it gives flexibility use the communication means of your requirement and choice.

Disadvantages

Although the simplicity of Web services is an advantage in some respects, it can also be a hindrance. Web services use plain text protocols that use a fairly verbose method to identify data. This means that Web service requests are larger than requests encoded with a binary protocol. The extra size is really only an issue over low-speed connections, or over extremely busy connections.

The problem with HTTP and HTTPS when it comes to Web services is that these protocols are “stateless”—the interaction between the server and client is typically brief and when there is no data being exchanged, the server and client have no knowledge of each other. More specifically, if a client makes a request to the server, receives some information, and then immediately crashes due to a power outage, the server never knows that the client is no longer active. The server needs a way to keep track of what a client is doing and also to determine when a client is no longer active.

Typically, a server sends some kind of session identification to the client when the client first accesses the server. The client then uses this identification when it makes further requests to the server. This enables the server to recall any information it has about the client. A server must usually rely on a timeout mechanism to determine that a client is no longer active. If a server doesn’t receive a request from a client after a predetermined amount of time, it assumes that the client is inactive and removes any client information it was keeping. This extra overhead means more work for Web service developers.

Example:

File -> New Website -> select Asp.net WebService Template

FirstService.asmx

<%@ WebService language=”C” %>

using System;
using System.Web.Services;
using System.Xml.Serialization;

[WebService(Namespace=”http://localhost/MyWebServices/&#8221;)]
public class FirstService : WebService
{
[WebMethod]
public int Add(int a, int b)
{
return a + b;
}

[WebMethod]
public String SayHello()
{
return “Hello World”;
}
}

run this service to get service url.

Web-Based Service Consumer :

File -> New Website

Add webservice, in solution explorer right click on project and select Add Webreference and provide above webservice URL.  So that webservice will be attached to consumer project.

Write a Web-based consumer as given below. Call it WebApp.aspx.

This application has two text fields that are used to get numbers from the user to be added. It has one button, Execute, that, when clicked, gets the Add and SayHello Web Services.

WebApp.axpx
<%@ Page Language=”C#” %>
<script runat=”server”>
void runSrvice_Click(Object sender, EventArgs e)
{
FirstService mySvc = new FirstService();
Label1.Text = mySvc.SayHello();
Label2.Text = mySvc.Add(Int32.Parse(txtNum1.Text), Int32.Parse(txtNum2.Text)).ToString();
}
</script>
<html>
<head>
</head>
<body>
<form runat=”server”>
<p>
<em>First Number to Add </em>:
<asp:TextBox id=”txtNum1″ runat=”server”  Width=”43px”>4
</p>
<p>
<em>Second Number To Add </em>:
<asp:TextBox id=”txtNum2″ runat=”server” Width=”44px”>5</asp:TextBox>
</p>
<p>
<strong><u>Web Service Result -</u></strong>
</p>
<p>
<em>Hello world Service</em> :
<asp:Label id=”Label1″ runat=”server”  Font-Underline=”True”>Label</asp:Label>
</p>

<p>
<em>Add Service</em> :
& <asp:Label id=”Label2″ runat=”server” Font-Underline=”True”>Label</asp:Label>
</p>
<p align=”left”>
<asp:Button id=”runSrvice” onclick=”runSrvice_Click”  runat=”server” Text=”Execute”></asp:Button>
</p>
</form>
</body>
</html>

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s