Re: Cardinality "highly unusual"

Matt M wrote:
> Hugo Kornelis wrote:
> ...
>> Based on your description, you've chosen the right cardinality. I don't
>> know if the statement of MS Visio EA about this type of cardinality being
>> rare is true or not. In any case, I wouldn't worry about it. It doesn't
>> sound like an error message - more like a warning. Consider it a
>> reminder:
>> the program tells you "this is unusual - you might want to double-check
>> if
>> you didn't make an error here".
>
> Hi Hugo
>
> Thanks, you've helped to set my mind at rest!
>
>> Is the text you're working from specifically written for your situation
>> (rare books, that are unique and can therefor be sold only once). I'm
>> asking because the solution from the book is exactly what a reular book
>> store would use (though I'd personally prefer to call the table "Titles"
>> instead of "Books" in a regular book store). The BookOrder table is used
>> to store the many-to-many relationship between Order and Book (title),
>> since in a regular book, each order has one or more books and each title
>> can be sold in zero or more orders.
>
> Right, you would use a composite entity to resolve a n:m relationship.
> That > makes sense if the bookshop sells new books. But my text (actually
> an MS book) deals explicitly with rare and unique books, and uses a
> composite entity to resolve a 1:m relationship between order and book.
> This strikes me as logically and conceptually wrong, but if it is the
> preferred way of doing things then so be it.
>
> Try as I might, I simply cannot generate this sort of schema from an ORM
> source model (my preferred modeling method). Instead, I have to do a lot
> of > tweaking of the logical diagram mapped from the ORM source model.

I clicked on the send button too hastily. Please ignore the bit about ORM at the bottom.

Thanks for your help

Matt Received on Tue Feb 15 2005 - 13:36:21 CET