Hi everyone,
When I first began preparing for my CIS-DF exam, I understood CMDB to be nothing more than a device database. While I might be able to memorize the definitions, I would not know why a CI had been duplicated or how one source would overwrite another. This gap was troubling me far more than any grade.
What helped resolve this issue was answering scenario questions, where each wrong option would be explained. There was one question in particular, dealing with duplicates, which made me realize the distinction between identification and reconciliation. Identification was what decided whether the record existed, while reconciliation decided which source was used for which attribute. Once I saw them as separate steps, many questions became much easier.
Another turning point was CSDM. It seemed like an endless amount of tables and layers at the beginning. However, after answering a couple of questions which explained the business service and asked where to put something in the model, I began thinking in terms of how the business service interacts with the underlying infrastructure. The model made sense when I knew why it was needed.
Eventually, when I started solving some ServiceNow CIS-DF exam practice questions on CertBoosters, I found that I would read the scenario of the actual problem and select the right tool later on. It was due to practice rather than any additional reading. I also tested ideas on a developer instance. Creating a duplicate CI on purpose and watching what happened taught me more than a chapter would.