Questions on WCF regarding Class lirbary and also reg. DataContract - wcf

Question

URL: http://wcftutorial.net/Introduction-to-WCF.aspx
Question 1:
Above tutorial mentions a Tip:-
a. Define the service in Class library and refer the class library in Host project. Don’t use service class in host project.
b. Always create the service with Interface->Implementation format, mention the contract in Interface.
c. Define the service in Class library and refer the class library in Host project. Don’t use service class in host project.
Question: Does the good practice suggest to create another class library rather then the existing IService1.cs and Service1.svc? Can anyone here give me an example of what author is trying to say in the above points?
Question 2:
When I create a new WCF application it has got IService1.cs and Service1.svc. All the implementation I have coded under Service1.svc.cs
Under the IService1.cs there is Service and Operation Contract, data contract (What is purpose of data contract here? can I delete it off?).
[ServiceContract]
public interface IService1
{
[OperationContract]
string GetData(int value);
[OperationContract]
CompositeType GetDataUsingDataContract(CompositeType composite);
// TODO: Add your service operations here
}
// 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; }
}
}

Answer 1

First of all, I would like to suggest you reading the basics of WCF in a book "Learning WCF" from Michele Leroux Bustamante, if you have an option to get it - the tutorial you are linking to was too chaotic by my opinion (I was reading it some time ago too)
Question 1: The thing is, that you should define 2 projects - 1 will contain host of the service and second will contain definition/implementation of that service. See picture below:
In ServiceHost, I ussualy have only main entry point, which launches the host. In ServiceLibrary (you can choose whatever name suits you) I have the service interface and implementation. Also, please notice that in ServiceHost, I have referenced ServiceLibrary.
Question2: Simply said: DataContracts are used when you are working with your custom objects over WCF. Lets say you want to get information about "Person" from you service. You can either define for example 3 OperationContracs - first would return name (string), second one age of that person (int) and third one telephone number (int).
But this is not the way you should proceed - you should return Person object from service (in your case, you have "CompositeType"). For that, you need to mark the class with [DataContract] attribute and all the information you want to exchange with [DataMember] attribute.
Of course you dont need to have the definition of "CompositeType" in IService - you can create new class in your project, name it "CompositeType" and mark it as [DataContract].
Is it more clear?

Answer 2

Answer of Question 1
Yes you need to create a separate class library for your service and a separate host project.See the following
You need to create something like this. Add Reference of AngService in AngServiceHost Application.
AngServiceHost Application is WCF Application. Delete the Service1.cs and IService1.cs
Add following lines in Service1.svc in AngServiceHost
<%# ServiceHost Language="C#" Debug="true" Service="AngService.ILogin" %>
Answer of Question 2
Whatever you have coded in .svc.cs file should go in the service class library, not in the host application.
Understand that the .svc file is used for hosting. You can reference the source of the service in this .svc file. In my example the dll of AngService (the class library) is added in AngServiceHost(the host application). This dll contains the actual code. You need to do something similar to this.