When a data provider cannot use the proposed value fields (for instance in data product type), how can he/she still provide some information to characterise his/her data sets?

1. How could we allow for extensibility? If we need to consider new kinds of science data product , not yet defined in the Obs/tap fields , how should we proceed?
2. Description of a data set - obs_title

In Obs/Tap , it is not a mandatory field, it could become important in future releases if its usage is well-defined. At the moment it is just free-format, and that could be an issue.