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  • Re: Derivation vs. Subset Constraint

    Rolemo For this example, I would choose to make the fact type &quot;Project is completed&quot; as simply derived. The subset constraint approach would create an extra Boolean column &quot;isCompleted&quot; 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 ...
    Posted to User experience (Forum) by Terry Halpin on Tue, Oct 21 2008
  • Re: how to define a supertype as secondary

    Apparently you are using an old version of Lab 4. We changed the way subtyping works so that now a solid arrow is always used if that path provides a way to the preferred identifier. I just sent Ken the latest version of Lab 4&nbsp;which he should place soon in the library. This shows solid arrows, as you are experiencing. Cheers Terry
    Posted to User experience (Forum) by Terry Halpin on Tue, Oct 21 2008
  • Re: frequency constraint

    Yes
    Posted to User experience (Forum) by Terry Halpin on Tue, Oct 21 2008
  • Re: communicating ORM diagrams to layman

    Rolemo, download NORMA Lab 5 from the library and see the slides on the report generator. You can generate a report with the model verbalized for clinet to approve. Cheers Terry
    Posted to User experience (Forum) by Terry Halpin on Tue, Oct 21 2008
  • Re: predicats and elementary facts

    Rolemo I assume you want to use &quot;exists&quot; as a unary predicate. The formalization of ORM instead&nbsp;always uses an existential quantifier instead of a predicate for&nbsp;asserting existence. So please do not use &quot;exists&quot; as a predicate. Cheers Terry
    Posted to Philosophy (Forum) by Terry Halpin on Mon, Oct 20 2008
  • Re: uniqueness constraints vs idetifiers

    Hi Rolemo In this example, EmpNr is the identifier for Employee. If you declare a reference mode for an entity type, that provides its preferred identifier. The expression Academic(.empNr) is short for the 1:1 mandatory existential fact type &quot;Academic has / is of EmpNr()&quot;. Cheers Terry
    Posted to User experience (Forum) by Terry Halpin on Mon, Oct 20 2008
  • Re: elementary fact types and functional dependencies (FDs)

    Hi Rolemo Facts may be compound or atomic. Atomic facts can&#39;t be rephrased as a conjunction of 2 or more smaller facts without information loss (with the same objects involved). Atomic facts are either elementary facts or existentail facts. Elementary facts apply a logical predicate to one or more objects, e.g. The Country identified by the ...
    Posted to User experience (Forum) by Terry Halpin on Sat, Oct 18 2008
  • Re: ternary fact types

    Rolemo Your ternray is correct as is. There are two constraints on it (a mandatory role constraint and a uniqueness constarint). When you combine the meaning of these constraints you obtain&nbsp;the meaning you were after (corresponding to a multiplicity constraint of 1 in UML -- we don&#39;t use UML&#39;s multiplicity constraint notation because ...
    Posted to User experience (Forum) by Terry Halpin on Sat, Oct 18 2008
  • Re: Terry's paper "Object-Role Modeling: an overview"

    Dear Rolemo Yes a predicate reading may contain nouns. In ORM, it is up to you what you wish to think of as an object (I call this &quot;object relativity&quot;). A predicate reading in ORM is the same as in predicate logic, viz. a sentence with object placeholders in it. You can phrase the sentence and choose the objects how you wish. ...
    Posted to User experience (Forum) by Terry Halpin on Sat, Oct 18 2008
  • Re: values vs entities

    Dear Rolemo In this case we chose to identify ranks by rank codes (e.g. &quot;SL&quot; for Senior Lecturer). We could instead have identified ranks by rank names (e.g. &quot;Senior Lecturer&quot;). Modeling it this way, we are&nbsp;talking directly&nbsp;about the ranks, rather than codes or names. I think this is&nbsp;probably how most people ...
    Posted to User experience (Forum) by Terry Halpin on Fri, Oct 17 2008
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