All true and good points, but if you feel the need to say that perhaps I was not being clear enough.

1. In the situation described so far, a relational database is almost certainly not the optimum solution.

2. If you must use a relational database, you can mimic the ability to accept arbitrary input using something equivalent to Varbinary(max) columns.

3. A non-relational database may be the optimum solution in your particular case, but perhaps it is not. Before using some form of key-value store or object oriented database etc, think about non-database solutions. Depending on precise circumstances perhaps simply writing the input out to a file or into an ordered file directory structure is a better fit. It may or may not be depending on further details.