  In his affirmative answer to the Edelman-Reiner conjecture, Yoshinaga proved
that the logarithmic derivation modules of the cones of the extended Shi
arrangements are free modules. However, all we know about the bases is their
existence and degrees. In this article, we introduce two distinguished bases
for the modules. More specifically, we will define and study the simple-root
basis plus (SRB+) and the simple-root basis minus (SRB-) when a primitive
derivation is fixed. They have remarkable properties relevant to the simple
roots and those properties characterize the bases.
