How address balance is calculated? It does not seem practical to scan every transaction on a block chain to determine the balance for an account.  As the block chain grows this seems even more difficult and resource consuming. Perhaps all the transactions are grouped into what we used to call a record, specifically a variable length record.
address..trans1, trans2, etc...transN  for the last transaction.
Bitcoin uses the so called UTXO (Unspent Transaction Output) model.
The first time it is not very intuitive because it is different from the traditional accounting model where you just spend from and send to an account.
Think about full piggy banks that can't be filled more than they are and that you have to break open before being able to spend the content: 

1) Bob has 1 piggy bank, he wants to pay Alice with half of the piggy bank's content
2) he breaks his piggy bank
3) he takes half of it and gives it to Alice, who will put it all in a new piggy bank belonging to her
4) you put the remaining half in a new smaller piggy bank belonging to you and which is waiting to be broken open.

Each piggy bank/UTXO is linked to an address.
A Bitcoin user can of course have several UTXOs related to his address. The sum of the UTXOs gives the amount of bitcoins owned by the address (which is one of the function of wallets).
Each transaction input is the output of a previous transaction.
Although wallet software gives the feeling that you "transfer" bitcoins or satoshis, you don't spend from an account you spend UTXO.
You spend from transactions previously made to you.