While I do not have a specific resource that explains this, I have done similar things millions of times.
My thoughts are this: For database structure, there are 3 core tables, one containing the body code forthe document, the next containing all of the unique keywords that you may use on your site (emphasis on unique, no need for dupes), and the last table for linking it all together. The body table will contain cells for the last updated date and time, as well as the author and any other relevant information you need.
Now how this all comes together is this. You make some sort of admin section that allows you to "assign" keywords to specific pages. When you assign a keyword to a page, a resord will be added to the 3rd table. That table would essentially only contain 3 columns. The first being a unique id number for that record, the second holding the id number of the body document, and the last containing the id of the keyword. Multiple records can be added for each body document with different keywords assigned to each.
Now of course comes the question of what the heck to do with all of it once it's gotten this far. Well, when you tell the page to pull the specific body document from the database, you tell it to select all of the instances of that body showing up in the linking table. This in turn will give you all of the unique id's of keywords associated with that document. Now with a while look, you have the database pull the record for each keyword based on the id number and build the meta keyword string as it goes.
As for showing the date modified and author info in the meta tags as well, just select those cells from the body document table when you select the body content. Should be pretty straight forward.
If you'r still lost, respond to this and I will try to explain it more.