5NF and Database Design

(kb.databasedesignbook.com)

81 pontos | por petalmind 5 horas atrás

8 comentários

  • Quarrelsome
    1 hora atrás
    Especially loved the article linked that was dissing down formal definitions of 4NF.
  • tadfisher
    4 horas atrás
    I love reading about the normal forms, because it makes me sound like I know what I'm talking about in the conversation where the backend folks tell me, "if we normalized that data then the database would go down". This is usually followed by arguments over UUID versions for some reason.
    • necovek
      4 horas atrás
      So which normal form do they argue for and against? And what UUID version wins the argument?
      • tadfisher
        3 horas atrás
        Explaining jokes is poor form.
        • necovek
          2 horas atrás
          This was an attempt to extend jokes and not ask for explanation: there are a number of normal forms, and people usually talk about "normalization" without being specific thus conflating all of them; out of 7 UUID versions, only 2 generally make sense for use today depending on whether you need time-incrementing version or not.
        • culi
          3 horas atrás
          On the internet it is normal.
      • Tostino
        4 horas atrás
        Not OP, but UUID v7 is what you want for most database workloads (other than something like Spanner)
        • RedShift1
          1 hora atrás
          Me still using bigints... Which haven't given me any problems. Wouldn't use it for client generated IDs but that is not what most applications require anyway.
        • tossandthrow
          2 horas atrás
          I use the null uuid as primary key - never had any DB scaling issues.
          • petalmind
            2 horas atrás
            Yeah, no NULL is ever equal to any other NULL, so they are basically unique.
            • Groxx
              1 hora atrás
              You are also guaranteed to be able to retrieve your data, just query for '... is null'. No complicated logic needed!
  • jerf
    3 horas atrás
    In a roundabout way this article captures well why I don't really like thinking in terms of "normal forms", especially as a numbered list like that. The key insights are really 1. Avoid redundancy and 2. This may involve synthesizing relationships that don't immediately obviously exist from a human perspective. Both of those can be expanded on at quite some length, but I never found much value in the supposedly-blessed intermediate points represented by the nominally numbered "forms". I don't find them useful either for thinking about the problem or for communicating about it.

    Someone, somewhere writing down a list and that list being blessed with the imprimatur of Academic Approval (TM) doesn't mean it is actually useful... sometimes it just means that it made it easy to write multiple choice test questions. (e.g., "What does Layer 2 of the OSI network model represent? A: ... B: ... C: ... D: ..." to which the most appropriate real-world answer is "Who cares?")

    • petalmind
      3 horas atrás
      > Someone, somewhere writing down a list and that list being blessed with the imprimatur of Academic Approval (TM)

      One problem is that normal forms are underspecified even by the academy.

      E.g., Millist W. Vincent "A corrected 5NF definition for relational database design" (1997) (!) shows that the traditional definition of 5NF was deficient. 5NF was introduced in 1979 (I was one year old then).

      2NF and 3NF should basically be merged into BCNF, if I understand correctly, and treated like a general case (as per Darwen).

      Also, the numeric sequence is not very useful because there are at least four non-numeric forms (https://andreipall.github.io/sql/database-normalization/).

      Also, personally I think that 6NF should be foundational, but that's a separate matter.

      • jerf
        3 horas atrás
        "1979 (I was one year old then)."

        Well, we are roughly the same age then. Our is a cynical generation.

        "One problem is that normal forms are underspecified even by the academy."

        The cynic in me would say they were doing their job by the example I gave, which is just to provide easy test answers, after which there wasn't much reason to iterate on them. I imagine waiving around normalization forms was a good gig for consultants in the 1980 but I bet even then the real practitioners had a skeptical, arm's length relationship with them.

    • wolttam
      2 horas atrás
      Why shouldn’t we care about layer 2? You can do really fun and interesting things at the MAC layer.
      • jerf
        2 horas atrás
        You can do what you do at the MAC layer without any regard for whether or not it is "OSI layer 2", or whether your MAC layer "cheats" and has features that extend into layers 1, or 3, or any other layer. Failing to implement something useful because "that's not what OSI layer 2 is and this is data layer 2 and the OSI model says not to do that" is silly.

        To stay on the main topic, same for the "normalization forms". Do what your database needs.

        The concepts are just attractive nuisances. They are more likely to hurt someone than to help them.

  • minkeymaniac
    1 hora atrás
    Normalize till it hurts, then denormalize till it works!
    • Quarrelsome
      1 hora atrás
      what a marvelous motto <3.

      Certainly a lot more concise than the article or the works the article references.

  • estetlinus
    4 horas atrás
    The lost art of normalizing databases. ”Why is the ARR so high on client X? Oh, we’re counting it 11 times lol”.

    I would maybe throw in date as an key too. Bad idea?

  • iFire
    2 horas atrás
    https://en.wikipedia.org/wiki/Essential_tuple_normal_form is cool!

    Since I had bad memory, I asked the ai to make me a mnemonic:

    * Every

    * Table

    * Needs

    * Full-keys (in its joins)

  • carlyai
    3 horas atrás
    love this
  • DeathArrow
    4 horas atrás
    There are use cases where is better to not normalize the data.
    • andrew_lettuce
      4 horas atrás
      Typically it's better to take normalized data and denormalize for your use case vs. not normalize in the first place. Really depends on your needs
      • jghn
        3 horas atrás
        Over time I’ve developed a philosophy of starting roughly around 3NF and adjusting as the project evolves. Usually this means some parts of the db get demoralize and some get further normalized
        • skeeter2020
          2 horas atrás
          >> Usually this means some parts of the db get demoralize

          I largely agree with your practical approach, but try and keep the data excited about the process, sell the "new use cases for the same data!" angle :)

    • petalmind
      3 horas atrás
      One day I hope to write about denormalization, explained explicitly via JOINs.
      • andrii
        1 hora atrás
        Please do, you content is great!
    • abirch
      3 horas atrás
      I'm a fan of the sushi principle: raw data is better than cooked data.

      Each process should take data from a golden source and not a pre-aggregated or overly normalized non-authorative source.

      • layer8
        3 horas atrás
        Sometimes the role of your system is to be the authoritative source of data that it has aggregated, validated, and canonicalized.
        • abirch
          2 horas atrás
          This is great. Then I would consider the aggreated, validated, and canonicalized source as a Golden Source. Where I've seen issues is that someone starts to query from a nonauthoritative source because they know about it, instead of going upstream to a proper source.
    • bob1029
      3 horas atrás
      JSON is extremely fast these days. Gzipped JSON perhaps even more so.

      I find that JSON blobs up to about 1 megabyte are very reasonable in most scenarios. You are looking at maybe a millisecond of latency overhead in exchange for much denser I/O for complex objects. If the system is very write-intensive, I would cap the blobs around 10-100kb.

      • Quarrelsome
        1 hora atrás
        I adore contiguous reads that ideas like that yield. I'd rather push that out to a read-only end point, then getting sucked into the entropy of treating what is effectively an unschema-ed blob into editable data.