The ORM Foundation

 As a follow-up to my previous response, the term "Period" has multiple dictionary meanings. It can mean simply a duration in time (e.g. 7 days), or instead an anchored duration in time with a specified start and end time (e.g. the period from 2015 Sep 11 to 2015 Sep 18). If your model needs both concepts, I suggest you use Duration ...

 Hi Jacob Of your three solutions, the one with Period(days) is preferable as that best captures the semantics. However, you should declare the reference mode to be unit-based -- it will then appear with an appended colon thus: Period(days:). As a minor change, I would rephrase the predicate reading to make it infix, e.g. Year(CE) limits ...

 Your wrote and reviewed examples sounds like two binary fact types: Person wrote Book; Person reviewed Book. There would be a pair-exclusion constraint between these fact types, so no person can write and review the same book. In this case, each argument of the exclusion constraint is a (Person, Book) role pair.   An exclusive-or ...

 As a follow-up to Andy's excellent explanation, the characterization of an exclusive-or constraint in "However, in Exclusive-or constraint, Entity A can use Role1 or Role2,but not both. I cant see the difference here." should have used "must" instead of "can".   An exclusive-or constraint combines an ...

Hi Berhanu Regarding the 1996 paper by Weber and Zhang, I disagree with some of the claims made in that paper, and not see "construct overload" as a problem for NIAM or ORM. It is not uncommon for people to argue that NIAM and ORM are too expressive in their graphical notations, but I believe it is very convenient for modelers to ...

 Hi Matt Yes, www.factbasedmodeling.org is the website for the FBM Working Group. To get access to the metamodel, I suggest you join the working group, which is chaired by Serge Valera (see the membership page).  Cheers Terry 

Hi Jacob The FBM metamodel contains numerous examples of verbalizations of derivation rules, but we have not yet published the dynamic rule syntax. Cheers Terry.

 Hi Jacob   As I indicated earlier, your problem can be handled more efficiently using a dynamic rule. We have specified extensions to ORM’s rule syntax to support such rules, which can refer directly to states immediately previous to a transaction (e.g. the previous bid), but have not yet implemented this rule syntax in NORMA, so ...

 Hi Jacob   First let me correct an obvious omission from my previous rule, which should have read as follows: * Bid1 is highest for Advertisement if and only if       that Bid1 is for that Advertisement and offers some Price1       and no Bid2 <> Bid1 and is for that Advertisement ...

 Hi Jacob   Assume the ORM schema contains the following fact types, each of which is mandatory and many-to-one. Bid(.Nr) is for Advertisement(.Nr). Bid is by Consumer(.Nr). Bid offers Price(USD:). Bid is made on Date(ymd).  Now you may define the derived fact type "Bid is highest for Advertisement" (optional, ...