ESL Discussion

Hello everybody, 

I am studying at the moment the topic of already and yet. As it seems, yet and already can be interchangeable. But I am not sure about it. 

My question is: Do you know the difference between the following sentences?: 

1. Have you booked the summer holiday yet? 

2. Have you booked the summer holiday already? 

Is there any difference? 

Thanks for you answers.