An active transformation can change the number of rows that pass through the transformation. For example, the Filter transformation is active because it removes rows that do not meet the filter condition.
A passive transformation does not change the number of rows that pass through the transformation.
You can connect multiple branches to a downstream passive transformation when all transformations in the branches are passive.
You cannot connect multiple active transformations or an active and a passive transformation to the same downstream transformation or transformation input group. You might not be able to concatenate the rows. An active transformation changes the number of rows, so it might not match the number of rows from another transformation.
For example, one branch in a mapping contains an Expression transformation, which is passive, and another branch contains an Aggregator transformation, which is active. The Aggregator transformation performs aggregations on groups, such as sums, and reduces the number of rows. If you connect the branches, Data Integration cannot combine the rows from the Expression transformation with the different number of rows from the Aggregator transformation. Use a Joiner transformation to join the two branches.