The ORM Foundation

 Thanks Ken and Matthew. I always appreciate the guidance that I get here. Copying an Entity Type across pages looks like it would involve a bit of extra work. So, for now, I think I will stick to the one page. I will update my profile as suggested by Ken. Cheers

My apologies if this is not the correct forum for a NORMA question. How do you re-use entity types? That is, I have an entity type "Postcode". I want it to repeat on the same page, to un-clutter my model. So, logically, there will still only be one Postcode entity type. But it will appear more than once on the page. Cheers.

Yes. You are correct. The subset constraint would be implied by virtue of that mandatory role constraint. My Bad. I guess my statement about PKs not containing NULLs stems from a lack of experience. I've never gone there. All I could see would be pain. I could not imagine an identifying attribute combination which contains unkown values. If ...

Hi Reiner, That subset constraint is definitely an improvement. And you would probably need another one running up to the 'has first' fact type from the 'has second' fact type. Personally, I think disjunctive reference is a really bad idea. Primary Keys (even composite keys) should never be able to contain an attribute with a ...

Hi Ken, Addressing  your points: Learning ORM: I have already learnt ORM (at least ORM1). That's not to say that I know it all. But I have a pretty good knowledge of it. I will have to buy the updated book and upskill to ORM2. So far, I have not had any trouble understanding any ORM2 diagrams. But I am sure there are many subtle ...

Thank you guys. My apologies - I still have not gone through all of the tutorials. I should do that before asking questions here (that will be answered there). I still have a lot to digest before I can give any sensible feedback.  But I can say that Matthew's suggestions (steps 1 and 2) at the object level were easy to get happening. ...

Hi There, I have a question with regards to the mapping of reference modes to the Relational View and the Relational Schema. I have an entity type, Customer. The reference mode for Customer is username. This maps as a PK called customerUsername in both the Relational View and the Relational Schema. I find customerUsername a bit clunky and would ...

Hi Ken, I learnt ORM at QUT as well. My tutor no longer works there. I believe he is now working in the industry. Sorry I cannot help you out with a contact.   Andy

 Hi Ken, Thanks for addressing that for me. Looks like I jumped the gun a bit. I think a big error message in red font would definitely do the trick - that is, when a user clicks post  without filling in that other textbox.  It's a great forum. ORM deserves a forum, and I'm glad that one came into being. Cheers.

Thanks Dave and Ken. I got the solution in a tutorial at university a couple of years ago. Our tutor had the solutions to the even numbered questions, which he would put on the screen for us to copy down. I have a big question mark next to it in my notes and vaguely recall that the tutor was not able to provide a good explanation which explained ...