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Derivation vs. Subset Constraint

Last post Tue, Oct 21 2008 16:42 by rolemo. 2 replies.
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  • Tue, Oct 21 2008 10:23

    • rolemo
    • Top 25 Contributor
    • Joined on Sun, Oct 12 2008
    • Posts 38

    Derivation vs. Subset Constraint

    Hi again,

    I'm trying to understand the difference between these two diagrams.

    I understand that there's a verbalization difference:

    • in the case of the derivation it means that the true value of one fact is derived from the other fact
    • in the case of the subset it means that the set of completed projects is a subset of thesuperset Project completed on Date

     Still, the bottom line is that a Project must be completed on some date in roder to be completed. So when should I use each?

    Thanks again (BTW, Terry - huge thanks for the labs, they're great Wink).


  • Tue, Oct 21 2008 13:20 In reply to

    Re: Derivation vs. Subset Constraint

    Rolemo

    For this example, I would choose to make the fact type "Project is completed" as simply derived. The subset constraint approach would create an extra Boolean column "isCompleted" which would then have to be kept in sync with the completionDate column (isCompleted set to true/false if completionDate is not-null/null). It seems easier to simply derive this on update rather than store it.

    Cheers

    Terry

    P.S. Ken is creating a NORMA Tutorials folder in the library that has the latest versions of the NORMA labs and related docs.

  • Tue, Oct 21 2008 16:42 In reply to

    • rolemo
    • Top 25 Contributor
    • Joined on Sun, Oct 12 2008
    • Posts 38

    Re: Derivation vs. Subset Constraint

    Sure good news about Ken's folder (though I hope i wont need it by the time its available). I may suggest to include a glossary. The only one I found (thanks to you actually) is focused on annotations, but hardly explains the proper use of them.

    What I'm thinking of is more of a lexical or encyclopedic type of glossary, presenting each concept or symbol and explaining in a sentence or few:

    • when and how to use it
    • common mistakes
    • what you must not forget when using it (an object must have a reference mode and data type)
    • alternative annotations and when to choose them

    I'd include some FOL basic concepts & relational DB as well.

    Now i know preparing it would be a mighty task, but it will be an interesting oneCool

     Cheers

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