What condition must be met for rules to transform attribute data during aggregation?

For rules to effectively transform attribute data during the aggregation process, it is essential that multiple source values must be available. This is because the aggregation process involves combining data from various identities or sources to create a comprehensive view. When multiple source values are present, rules can be applied to determine how to consolidate or manipulate this data in a meaningful way.

Having multiple values allows the rules to consider different inputs and define transformation logic that reflects a more accurate representation of the aggregated attribute. This is particularly important when dealing with attributes that may vary between sources or when there are conflicting values. Without multiple source values, there would be limited opportunities for the rules to operate, reducing the effectiveness of the aggregation process significantly.

The other conditions listed do not directly relate to the fundamental requirement of having diverse inputs for the aggregation transformation to occur successfully.