That's what prototyping and peer review are for, I write up a schema, send to everyone else on the team, get feedback. If users are invovled get it from them

That's what prototyping and peer review are for, I write up a schema, send to everyone else on the team, get feedback. If users are invovled get it from them too.... take in all the feedback, write up a new draft, wash, rinse, repeat until running out of shampoo (i.e. feedback)..... Once things are pretty stable, do a prototype, address any oversights, do the real thing. It's not rocket science.