Which linguistic innovation dramatically improved retail chatbots' ability to understand customer intent after 2018?

Retail chatbots have revolutionized customer service by incorporating sophisticated natural language processing technologies. Behind these seemingly simple interfaces lies complex linguistic architecture that enables human-like interactions. This trivia question explores a significant linguistic breakthrough that changed how retail chatbots understand and respond to customer queries. Test your knowledge about the intersection of computational linguistics and retail technology!

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BERT (Bidirectional Encoder Representations from Transformers) contextual language models
Simple keyword matching with Boolean operators
WordNet-based synonym expansion
Rule-based grammatical parsing (RBGP)