Today we are working with Stored Procedures to access the database.
In order to allow unit testing, we implemented an interface for each group of related stored procedures, for example:

```
ICustomerRepository
{
 GetAllCustomer();
 GetCustomerById();
 GetEnrolledCustomers();
 // etc..
}

```

We plan to implement DDD in all projects. 

My question is in which DDD layer its best to put the implementation of these interfaces and why? 

Please consider that its a huge 4 years project so for now, we will not be able to make changes in how our DAL works. Thanks!