What is the difference between an index system and an electronic database ?

When researching information regarding evidence-based practice associated with hand hygiene methods and products used when caring for a patient-ordered contact precaution, you could access the library’s nursing databases.

What is the difference between an index system and an electronic database ?
What different attributes/features would you use to conduct an effective, concise online search for appropriate nursing literature?
What advantage will a federated search provide for your search?
This doesnt have to be in a certain format or have a cover page. You can just answer each question with a few sentences and that will be fine.