> Normal forms not required.
3NF (approximately where document databases live) struggles to decouple the time domain from individual facts. Let me give you an example.
Assume a Customer document has a LastModifiedUtc property. Does this tell you when their email specifically changed? No. It just says "something" in the customer document was modified.
Now, you could say "how about we just add a property per thing I want to track?" Ok - so we now have Customer.EmailLastModifiedUtc, Customer.NameLastModifiedUtc, etc. This is pretty good, but now assume we also need to know what the previous email addresses and names were. How do we go about this? Ok - no big deal, lets just add another column that is some JSON array or whatever. Customer.PreviousEmailAddresses. Cool, so now we know when the email was last modified AND we know what every last variant of it was.
What is missing? Oh right. What about when each of the previous email addresses actually changed? Who changed it? From what IP address? Certainly, we could nest a collection of documents within our document to keep track of all of this, but I hope the point is starting to come across that there may be some value in exploring higher forms of normalization. Imagine if I wanted to determine all of the email addresses that were modified by a specific IP address (across ALL customers), but only over the last 25 days. I feel like this is entirely out of the scope of a document database.
Don't get me wrong. 3NF is extremely powerful and handles many problem domains with total ease. But, once you start talking about historization of specific fields and rates of change, you may need to consider something higher order.
Map the index additions and their timestamps onto the documents themselves and you can retrieve the entire state of each record that the ip wrote at the time that it wrote it. If you want to know specifically what that ip changed, then diff it with the previous record, for example, to filter down to updates that only changed the email address.
