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Binary fact type with spanning uniqueness constraint in co-referenced form. Independent?

Last post 08-26-2011 2:47 by JackStoneS. 2 replies.
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  • 08-24-2011 4:08

    Binary fact type with spanning uniqueness constraint in co-referenced form. Independent?

    I have a question regarding schema equivalence.

    In the attached image, I have put two versions of a simple schema.
    An actor (with an id and name) can play in more than one play.
    A play (with a code and title) can involve multiple actors.

    When I write the fact type with a spanning uniqueness constraint in co-referenced form, I get something like the second schema.
    Is it necessary to mark the entity type ActorPlaysInPlay is independent? It plays no roles except for those that identify it, but we need to populate this in the database.
  • 08-24-2011 15:31 In reply to

    Re: Binary fact type with spanning uniqueness constraint in co-referenced form. Independent?

    Hi Jack,

    The spanning uniqueness constraint on the binary creates an implied objectification, which has a coreferenced form as you present. The entity type for an implied objectification is always marked as independent, and you will need to do the same for your expanded form if you want to create a separate table for it in the database.

    Just curious: why do you want the coreferenced form in your model instead of the spanning uniqueness?

    -Matt

  • 08-26-2011 2:47 In reply to

    Re: Binary fact type with spanning uniqueness constraint in co-referenced form. Independent?

    Thanks for your reply!

    For my thesis I'm working on a proof of concept of an algorithm to translate ORM schemas into UML. Because I want the UML schemas to be close to the relational model, and I do not have much time left, I want the binaries with a spanning uniqueness constraint in co-referenced form.
    If I rewrite an ORM schema in its most basic form (no spanning uniqueness, no binaries, no unaries, no objectification), I can greatly reduce the number of concepts I have to consider.
    Knowing that the co-referenced form needs to be marked as independent helps deciding it needs to be mapped to a class.
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