Seq2Seq and Encoder-Decoder
Translation, summarisation, and question answering all share a structural challenge: the input and output are both sequences, but rarely the same length, and the alignment between them isn't fixed. The encoder-decoder architecture solved this by splitting the problem into two halves — compress the input, then generate the output — and it framed the field's central problem for the next several years, including the one it couldn't quite solve on its own.