Difference between a Fill and a Transaction

Fills and Transactions are separated from each other for the following reason. A Fill contains all the information received from the broker / exchange (and a reference to the Order). Whereas a Transaction contains all the information related to accounting (i.e. references to position and strategy). In addition to Transactions related to Fills, there are Transactions that are independent of Fills (i.e. Deposits, Withdrawals, Interest, etc.).