pseudocode description of transfer in AXI

Hello I am  new to AXI and just saw the pseudocode for a transfer in the spec of AXI . My question is regarding Data_Bus_Bytes .

Q1-  The spec says that Data_Bus_Bytes is  number of 8 bit byte lanes in the bus. Is it same  as Number_Bytes which is 2^AWSIZE ?

Q2 - where are we going to use Upper byte lane and lower byte lane further?