In attention, a query represents what the model is looking for. It is compared with keys to score relevance; those scores weight the values that are combined. In sequence models, the query can come from the target sequence, while keys and values come from the source. section 15.3.1
Figure 15.6 Retrieving images from a database: the query is compared to a set of keys, and the match scores are used to rank values (images).
A photo-search analogy: compare the query with photo tags (keys), then use match scores to rank the photos (values). section 15.3.1






