• A secure service to process business transactions.
• A service that supplies current data to others, such as a traffic report or other monitoring service.
• A chat service that allows two people to communicate or exchange data in real time.
• A dashboard application that polls one or more services for data and presents it in a logical presentation.
• Exposing a workflow implemented using Windows Workflow Foundation as a WCF service.
• A Silverlight application to poll a service for the latest data feeds.

• It combines functionalities of Asp.Net Web services, remoting, MSMQ and Enterprise Services.
• It’s more reliable and secured then Web services.
• All the major changes can be done in the configuration file instead of code file.

• WCF has [ServiceContract] attribute attached with the class.
• WS has [WebService] attribute attached with the class. 
  
• WCF has [OperationContract] attribute attached with methods. 
  
• WS has [WebMethod] attribute attached with methods.
• WCF can be hosted on IIS, WAS, of self-hosting.
• WS can be hosted on IIS.

• WCF uses using System.Runtime.Serialization; namespace for serialization. 
• WS uses using System.Xml.Serialization; namespace for serialization.

• WCF support HTTP, TCP, MSMQ, P2P transport protocols. 
• WS support Http protocol.

• WCF supports XML, MTOM (Messaging Transmission Optimization Mechanism), Binary. 
•  WS supports XML, MTOM, DIME (Direct Internet Message Encapsulation).

• WCF provides reliable security for messaging and transactions over net.
• WS doesn’t provide method level security & message delivery isn’t assured & can be lost without acknowledgement.

It has 2 attributes : 
[ServiceContract] and [OperationContract]
[ServiceContract]
    public interface IService1
    {
        [OperationContract]
        string GetData(int value);
        [OperationContract]
        CompositeType GetDataUsingDataContract(CompositeType composite);
        // TODO: Add your service operations here
    }

 [DataContract]and [DataMember]
// Use a data contract as illustrated in the sample below to add composite types to service operations
[DataContract]
    public class CompositeType
    {
        bool boolValue = true;
        string stringValue = "Hello ";
        [DataMember]
        public bool BoolValue
        {
            get { return boolValue; }
            set { boolValue = value; }
        }
        [DataMember]
        public string StringValue
        {
            get { return stringValue; }
            set { stringValue = value; }
        }
    }

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.web>
    <compilation debug="true" />
  </system.web>
  <!-- When deploying the service library project, the content of the config file must be added to the host's
  app.config file. System.Configuration does not support config files for libraries. -->
  <system.serviceModel>
    <services>
      <service name="WcfServiceLibrary1.Service1"behaviorConfiguration="WcfServiceLibrary1.Service1Behavior">
        <host>
          <baseAddresses>
            <add baseAddress = "http://localhost:8731/Design_Time_Addresses/WcfServiceLibrary1/Service1/" />
          </baseAddresses>
        </host>
        <!-- Service Endpoints -->
        <!-- Unless fully qualified, address is relative to base address supplied above -->
        <endpoint address ="" binding="wsHttpBinding" contract="WcfServiceLibrary1.IService1">
          <!--
              Upon deployment, the following identity element should be removed or replaced to reflect the
              identity under which the deployed service runs.  If removed, WCF will infer an appropriate identity
              automatically.
          -->
          <identity>
            <dns value="localhost"/>
          </identity>
        </endpoint>
        <!-- Metadata Endpoints -->
        <!-- The Metadata Exchange endpoint is used by the service to describe itself to clients. -->
        <!-- This endpoint does not use a secure binding and should be secured or removed before deployment -->
        <endpoint address="mex"binding="mexHttpBinding"contract="IMetadataExchange"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior name="WcfServiceLibrary1.Service1Behavior">
          <!-- To avoid disclosing metadata information,
          set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="True"/>
          <!-- To receive exception details in faults for debugging purposes,
          set the value below to true.  Set to false before deployment
          to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="False" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>