The Beginning balance is using the BEGIN_BALANCE_DR_BEQ and BEGIN_BALANCE_CR_BEQ values from GL_BALANCES table.
How these values are obtained:
In the case of a Income Statement account, each journal line to the account combination in the foreign currency (in this case EUR) is converted based on a rate.
Starting with the first journal line posted in the new year the converted value is stored in the PERIOD_NET_DR_BEQ PERIOD_NET_CR_BEQ columns in GL_BALANCES table.
Say Jan 15 there is an entry for DR 1 EUR at a 1.5 conversion rate to XXX functional currency. - this becomes Period_net_dr = 1 and PERIOD_NET_DR_BEQ = 1.5
When Feb period is open this now becomes the Feb BEGIN_BALANCE_DR_BEQ = 1.5
Feb Journal similar to Jan entry for DR 1 EUR at a 1.6 conversion rate to XXX functional currency. - this becomes Period_net_dr = 1 and PERIOD_NET_DR_BEQ = 1.6
When Mar Period is open this now becomes the Mar BEGIN_BALANCE_DR_BEQ = 3.1
The BEQ columns are all based on the conversion rate value of each individual journal line and are accumulated over the periods.
For Income Statement accounts this would zero at the beginning of each new year.. for balance sheet accounts this would just be a continued accumulation over time.