I agree with you, but would like to add that by using SQL to query a relational database it is very, very easy to denormalize the data that is copied into an ap

I agree with you, but would like to add that by using SQL to query a relational database it is very, very easy to denormalize the data that is copied into an application, so while a relational schema is essentially "static", query results are very dynamic, and can easily strip away all of the "goodness" that results from a normalized data structure. In other words, the application probably needs to deal with normalization and schema if it's taking copies of data, and using a relational database doesn't remove this requirement. (Of course, small applications often get away without enforcing schema, with the understanding that frequent database write failures due to malformed data are ok.)