Given a transaction running on the Relational Database, firing a number of Chooses.

I'm assuming when in the center of this transaction, every other transaction commits some UPDATE or Place from the database, this new information is VISIBLE for that relaxation from the remaining chooses within the former transaction. Is assumption correct?

I am talking about, I'm assuming the transaction isn't isolated for reading through (it always reads the final condition from the Database even when it changes in the intervening time), only for that documents, could it be?

If the is dependent around the the transactional policy of every RDBMS, what's the policy of Oracle?

Your assumption is correct, a minimum of for Oracle.

Oracle guarantees the consistency of the read carried out in a given moment. When the read is started, it does not matter if other transactions alter the data being selected - Oracle guarantees the information is exactly what is at the database at the beginning of the read. Whether it can't recognition that guarantee, you receive an "ORA-01555 snapshot too old" error. However, subsequent chooses might not obtain the same answer.

To be able to provide read isolation/repeatable reads, you need to quit some concurrency, because you need to lock the table against updates. Oracle made a decision to be highly concurrent - visitors don't block.

If you are just searching for data in a given time, Oracle provides flashback queries.

Copy&Pasting the solution given as comment towards the question:

The default isolation level in Oracle is "read committed" (you "see" changes committed by other transactions, even when these were committed after your transaction began). Oracle also enables you to definitely set the isolation level to "serializable" (you simply "see" changes that were committed by other transactions at that time your transaction began) or "read only" (like "serializable", with the exception that it doesn't let it Place, UPDATE, or Remove). For the particulars, see link.