Need explanation for stock accounting system

Dear developers,

I have some vague concepts in my mind about stock accounting in OpenERP. I need someone in accounting to help me explain this.
1. OpenERP does not distinguish periodical stock from perpetual stock accounting
When enabling Inventory Valuation property to 'Real Time', it automatically calculate 'Stock Input Account', after reception, it transfers Stock Input Account to 'Stock Variation Account'.

I think OpenERP should do like this. It should provide 2 options: periodical or perpetual inventory method.
* with option 'periodical inventory method', we should have one account Stock Input Account (expense type, on P/L statement). At the end of period, Stock Variation Account should be updated to reflect inventory closing balance. Stock Output Account is used for COGS calculation (at the end of period).

* with option 'perpetual inventory method', we should update 'Stock Variation Account' directly when purchase/sell products. Stock Output Account is still used for COGS calculation concurrently.

These follow accounting principles that I've learned. OpenERP is merging these, makes setting up accounting system difficult.

2. OpenERP should support FIFO/LIFO costing method. Currently, it supports only fixed cost and average cost.

3. OpenERP has Expense Account in product form. I think it's redundant, making issues.
* with 'periodical inventory method', Expense Account should be 'Stock Input Account' (Expense type, P/L statement)

* with 'perpetual inventory method', Expense Account should be 'Stock Variation Account' (Asset type, Balance sheet statement)

Anyway, with Expense Account, Stock Input Account, Stock Variation Account, these are redundant, making issues to accounting system. It should be the same account, depending on context of inventory method.

Thanks.