How to implement Interfaces in the Data access layer?

Question

IDE : VS 2008,

Platform : .NET 3.5,

Hi,

I typically dont create interfaces unless i have to, however in my current application i have to create interfaces in the Data access layer. I'm a in a minor confusion that hwo do i create those interfaces more how to implement them:

the following code might make things clear:

I have the following class and interface in the data access namespace

 

using ConsoleApplication8.BusinessLayer;
using 
ConsoleApplication8.DataAccessLayer ;
using System.Data ;
using System 
;

Namespace DataAccessLayer 

{

    Public Class CountryGateway : 
ICountryGateway 
     {      
        public 
void InitCountry() 

         {

             //write 
code 

         }

                
        public 
Int32 saveCountry(ByRef obj As Country) 

      {

            //write 
code 

      }


        // 
        //implementation 
for other methods SearchByIndex() SearchByName and 
UpdateCountry() 
        //
        //

   }

    Interface 
ICountryGateway {
        void 
InitCountry() ;
        Int32 
saveCountry(ref obj As 
Country) ;
        DataSet 
SearchByIndex(countryNo As 
String)
        DataSet 
SearchByName(countryName As 
String);
        Int32 
updateCountry(ref country As 
Country);
    }




}

Namespace 
BusinessLayer {

    Public Class Country 
{

    }


}

1. Is this way implement the interface in the data access layer? (in this case the class CountryGateway access the database.) i.e:  That we should create interfaces to access DB in the DAL and then we should also write the implementation for those interfaces in the DAL?

2. I have been told that we should create interfaces than abstract classes espcially in the data access layer, is there a particular reason for this?