在面向对象的应用程序开发中，类的接口是一个很重要的概念，在.net框架中，.net不仅提供了强大的面向对象的特性，而且它也给我们提供了一系列强大的接口供我们使用，好了我们就来看看petshop3.0中的接口层，从解决方案管理器中的PetShop.IDAL命名空间中，我们可以看到几个接口：IAccount、IInventory、IItem、IOrder、IProduct、IProfile，我们以IAccount为例：
//References to PetShop specific libraries
//PetShop busines entity library
using PetShop.Model;
namespace PetShop.IDAL
{
/// <summary>
/// Inteface for the Account DAL
/// </summary>
public interface IAccount
{
/// <summary>
/// Authenticate a user
/// </summary>
/// <param name="userId">Unique identifier for a user</param>
/// <param name="password">Password for the user</param>
/// <returns>Details about the user who has just logged in</returns>
AccountInfo SignIn(string userId, string password);
/// <summary>
/// Get a user's address stored in the database
/// </summary>
/// <param name="userId">Unique identifier for a user</param>
/// <returns>Address information</returns>
AddressInfo GetAddress(string userId);
/// <summary>
/// Insert an account into the database
/// </summary>
/// <param name="account">Account to insert</param>
void Insert(AccountInfo account);
/// <summary>
/// Update an account in the database
/// </summary>
/// <param name="Account">Account information to update</param>
void Update(AccountInfo Account);
}
}
