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philipxy
philipxy
4:11 AM
@MDCCL There is nothing wrong with having a surrogate/arbitrary letter id chosen arbitrarily uniquely when a letter enters the system if sufficient natural candidate key columns don't happen to be needed in the database. Just as there is nothing wrong with, say, a driver's license number (whether you consider that as identifying a license, a driver, or both). Names and ids are not "meaningful", they are arbitrary (although you might choose a unique description as a name/id).
@Igor See my letter id comment in chat.
 
 
17 hours later…
Igor
Igor
9:44 PM
@MDCCL
13. Actually, I'm not very interested in what was the accident but more what happens with letters. (so they can return or be lost)
14. Yes (or in my edited answer where I added delivery attempt - couries takes letter to a person)
15.It is a part of university project, it will not be used in real life. My original intention when posting this question was to get answer if diagram which I had created (very basic) was correct, and what could be improved, I thought that it would be possible for some viewers to just say "it's ok" or "it's bad". I see now that it's not so easy, when you don…
 

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