BERT

The query "2019 brazil traveler to usa need a visa" turns on its smallest word. "To" makes the traveller a Brazilian bound for the United States, and it does so only in the light of the words on both sides of it. Google's ranking missed that and returned pages about U.S. citizens travelling to Brazil. The query was the company's own example on 25 October 2019, when it announced that a year-old research model would now help rank search results and that "BERT will help Search better understand one in 10 searches in the U.S. in English." A model that reads a query once, left to right, can only give "to" the context that came before it.