TY - JOUR
T1 - Why Self-Attention Is Natural for Sequence-to-Sequence Problems? A Perspective from Symmetries
AU - Ma , Chao
AU - Ying , Lexing
JO - Journal of Machine Learning
VL - 3
SP - 194
EP - 210
PY - 2023
DA - 2023/09
SN - 2
DO - http://doi.org/10.4208/jml.221206
UR - https://global-sci.org/intro/article_detail/jml/22012.html
KW - Self attention, Symmetry, Orthogonal equivariance, Permutation equivariance.
AB - <p style="text-align: justify;">In this paper, we show that structures similar to self-attention are natural for learning many sequence-to-sequence problems from the perspective of symmetry. Inspired by language processing applications,
we study the orthogonal equivariance of seq2seq functions with knowledge, which are functions taking two
inputs — an input sequence and a knowledge — and outputting another sequence. The knowledge consists
of a set of vectors in the same embedding space as the input sequence, containing the information of the
language used to process the input sequence. We show that orthogonal equivariance in the embedding space
is natural for seq2seq functions with knowledge, and under such equivariance, the function must take a form
close to self-attention. This shows that network structures similar to self-attention are the right structures
for representing the target function of many seq2seq problems. The representation can be further refined if
a finite information principle is considered, or a permutation equivariance holds for the elements of the input
sequence.</p>