Just my 0,02EUR
I'm not trying to promote the creation of tables w/o PKs, but just FYI - I work with the Baan ERP application (you've probably never heard of it, but I think they used to be #5 behind SAP, Oracle, etc. - Boeing is their largest customer) and they do not use PKs or any RI in the database - they use unique indexes with not null constraints, and they manage all the RI w/in the application. Not ideal, but I must admit they've done a pretty good job of implementing it this way - it's never caused us any problems in the 8yrs I've been working with it. I've heard that some of the other big ERPs (maybe even SAP - anyone know?) are designed similarly.
Another thing to consider in letting the app manage the RI is that you can't easily view the relationships for reporting purposes when trying to use Crystal or some other 3rd party reporting tool.
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