As far as interfaces go, we are talking specifically about functional interfaces (UDF's, or "User Defined Functions", and stored procedures). Raw interfaces like SQL queries have very different profiles of issues. This is one principle that more or less takes care of itself in most databases due to existing concerns regarding normalization and the like. Subtle violations are quite possible, however, but they can be avoided by careful design and the signs are relatively easy to spot. Problems can occur in both purely relational and object-relational designs though.