public static void DemoRun()
{
// We have defined an interface IRepository
// And we implement 2 classes SQL and SharePoint
// which does serve the common purpose to Save and Retrieve the recods.
// Observe, with this design, we are making the classes
// to be extendible but not modifiable.
// These classes can be further extended to add more features
// but need not have to be modified.
// SQL way
IRepositoryConnection connection = new SQLRepositoryConnection();
IRepository repository = new SQLRepository(connection);
AppData data = repository.Retrieve(1);
repository.Save(data);
// SharePoint way
connection = new SharePointRepositoryConnection();
repository = new SharePointRepository(connection);
data = repository.Retrieve(1);
repository.Save(data);
}