Well you have the BMC documentation but I guess the best part would be BMC formations.
Start to gloom CMDB projects if any..practically its quiet different to face issues and its resolution...
You can start with following documents
1. BMC Atrium Concepts and Planning Guide.
2. BMC Atrium CMDB User Guide.
These documents give you detailed idea about CMDB .
After these documents you can go through
3.BMC Atrium CMDB Normalization and Reconciliation Guide
I am also a CMDB learner recently and my reading guideline is as following:
Step-by-Step Approach for Building and Managing your CMDB.pdf
160635_AtriumCore7.6.03_ConceptsPlanningGuide.pdf (for AIE part)
BMC Atrium CMDB 7.6.04 Data Model Help HTMLs
Once you are done with “BMC Atrium Concepts and Planning Guide” read “Normalization and Reconciliation guide”
Once you are comfortable with CMDB/NE/RE concept you can move to AIE/AI documentation