Question: What are the source and target domains?
Answer: Book, electronics, beauty, music, IMDB, Yelp, cell phone, baby, DVDs, kitchen
Alternative answer: we use set 1 of the source domain as the only source with sentiment label information during training, and we evaluate the trained model on set 1 of the target domain, Book (BK), Electronics (E), Beauty (BT), and Music (M)