Determining the Leading System Attributes

Hi All

We are just installing Identity Management 7.2 and I'm preparing for the intitial load of one of our 9 ABAP systems, but I'm having difficulty with the term Leading System and it's meaning.

Section 3.4.5.1 - Determining the Leading System for Attributes notes that this step is very important and if we don't specify the leading system per attribute correctly attributes could be over written from other systems, leading to unexpected results.

I'm definately unclear with this concept. For example we plan on connecting IdM to 9 different systems (3 - Dev, 3 QA & 3 Prod), each having different User master data and privileges.

Is this section asking me to determine which of these 9 systems is going to be the Leading System, meaning all of the other 8 systems might have their User data overwritten by this systems, or is it asking for of the 9 systems, which is the Leading system, the Source or the IdM system?

Ken