There's no silver bullet I guess but I think the trap that one could fall into here is to think of "the" frontend. There's a bunch of additional consumers of the data model even for a single web-app. Auditing, security, reporting (prior to moving to a separate reporting database), internal tools, possible future mobile or desktop applications, etc. I have found the safest approach is to enforce invariants in the database rather than assume the application code will do the right thing. But as you highlight the schema can be refined by the needs of the front-end, especially where indexing is concerned.