Hi,
I'm hoping someone with more experience with ORM than me, and/or a better grasp of logic, can help with the following scenario (which is part of an ORM model with the Objects' and Facts' text changed - hence some of the Facts may appear a little strange).
I have a Cat Show where people may show their cats. Each Person must sponsor a Pennant. The constraint that I want to show in the model is: the Colour of the Pennant sponsored by a Cat's Person must be the same Colour as the Collar worn by that Cat. A diagram is attached.
I have tried a number of variations of the constraint, and although the verbalisations of some are along the lines I'm after; to me, none are clear enough to accurately describe the desired constraint. For examples, I can get:
"For each Colour, that Colour describes some Pennant if and only if that Colour describes some Collar." [1]; or
"For each Colour and Person, that Colour describes some Pennant if and only if that Colour describes some Collar." [2a]; or
"For each Colour and Cat, that Colour describes some Pennant if and only if that Colour describes some Collar." [2b]; or
"For each Colour and Cat and Person, that Colour describes some Pennant if and only if that Colour describes some Collar." [3].
[2b] appears the most succinct, but I don't know whether it is correct and sufficient. Thoughts, anyone?
Thanks, Peter
ps If the picture doesn't appear after this is posted, can someone tell me how to include a picture? (I've tried paste from Word and paste from clipboard and "Insert/edit image" button, and can't see any results.