> Hi, can you give an example? Not sure I understand what you're getting at there. An utterly trivial example is constraining the day-field in a date structure

> Hi, can you give an example? Not sure I understand what you're getting at there. An utterly trivial example is constraining the day-field in a date structure. If your constraint is at the level of the field then it can’t make a decision as to whether 31 is a good day-value or not, but if the constraint is at the record-structure level then it can use the month-value in its predicate and that allows us to constrain the data correctly. When it comes to schema design it always helps to think about how to ‘step up’ to see if there’s a way of representing a constraint that seems impossible at ‘smaller’ schema units.