C+Builder 5, IBO 3.6Cf, Interbase 6.01

I'm now starting on handling transactions.
The situation I would get is:
- a simple sales system with CUSTOMERS, ARTICLES, ORDERS
(master+detail)
- 2 users doing simultaneously an order with the same article
- each detail_order must update table ARTICLES, decreasing "remainder
stock"
I'm using 2 TIB_Query for ORDER_MASTER, ORDER_DETAIL, and there is a
trigger
for ORDER_DETAIL BEFORE INSERT that updates the table ARTICLES. Both
TIB_Query are associated with an IB_Transaction, Isolation=tiCommited.
My tests conclude that until first user commits his transaction,
second user
will get "deadlock".

I read more on help file, and I find RecVersion property on
IB_Transaction:
"This property only takes effect when Isolation is set to
tiCommitted...
...Setting this property to true will avoid deadlocks by allowing
uncommitted changes in the database to be ignored. Only the most
recent committed changes will be visible. I consider this
the "friendly" mode of committed isolation."

But I don't get any difference setting this property to true.
Is there anything I don't well understand?
Really, is there a way to allow multi-users update same record, on a
kind of "queue" without locking?
Must I look at mirror and wonder where I'm from?
Some help, please.
Hugo.