Oracle Database Discussions

Hi guys, i am getting very very very confused about how oracle implement consistency / multiversioning with regards to SCN in a data block and transaction list in the data block..

I will list out what i know so you guys can gauge me on where i am..

When a SELECT statement is issued, SCN for the select query is determined. Then Blocks with higher SCN are rebuilt from the RBS.

Q1) The SCN in the block implied here - is it different from the SCNs in the transaction list of the block ? where is this SCN store ? where is the transaction list store ? how is the SCN of the block related with the SCNs in the transaction list of the block ?

Q2) can someone tell me what happen to the BLOCK SCN and the transaction list
of the BLOCK when a transaction start to update to a row in the block occurs.

Q3) If the BLOCK SCN reflects the latest change made to the block and If the SCN of the block is higher then the SCN of the SELECT query, it means that the block has change since the start of the SELECT query, but it DOESNT mean that the row (data) that the SELECT query requires has changed.
Therefore why cant ORACLE just check to see whether the row has changed and if it has, rebuilt a block from the RBS ?

Q4) when ORACLE compares the BLOCK SCN, does it only SCAN for the BLOCK SCN or does it also SEARCH through the TRANSACTION LIST ? or it does both ? and why ?

Q5) is transaction SCN same as Transaction ID ? which is store in the RBS , the transaction SCN or ID ?

Q6) in short i am confuse with the relationship between BLOCK SCN, transaction list SCN, their location, their usage and relationship of the BLOCK SCN and transaction list when doing a SELECT, their link with RBS..

any gurus clear to give me a clearer view of what is actually happening ?