Charles manages application servers and database servers for a mid-sized company. He has access to books with security guidelines for the seven domains of an IT infrastructure. What domain should he refer to first for guidance with his job function?

Since Charles has access to books with guidelines for the seven domains of an IT infrastructure, he should first refer to The User Domain for guidance with his job function as Database Manager

Explanation:

IT infrastructure refers to the physical, software and network components that make up the foundation of a an IT service.

There are basically seven IT components. According to your question, Charles has access to books with security guidelines for all of them.

These Seven IT domains are:

To get guidance with his Job functions, Charles should refer to the user domain first because the user domain covers all the users (of any rank) that have access to the other six domains.