Query, key and value

With $X$ of shape $(n, d_{model})$, $Q = XW_Q$, $K = XW_K$ and $V = XW_V$ have shape $(n, d_k)$. The roles are not given: they are what training makes the projections do. The weights $\operatorname{softmax}(QK^\top / \sqrt{d_k})$ are computed from the input, while $W_Q$, $W_K$, $W_V$ are the parameters.