In the first case, a return is calculated separately for the long and the short positions in the portfolio. For example, the following figure shows the returns for the long positions are separate from the short positions. Notice that EMC is held both long and short in offsetting positions.
There is a limitation to the functionality. If the long and short positions are not combined, you cannot commit security level returns to the database. In other words, you can commit a total portfolio return, a long segment return, and a short segment return, but you cannot commit security level returns. This is because the PERFORM database is structured to store only a single position in each security, per fund per day.
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