Letor: Feature sub-classes question

Hello James,

I am working on breaking down Features into sub-classes. Should each of the
features get their own sub-class, or should the grouping be done according
to type? i.e. query-document pair dependent, query-dependent and document
dependent sub-classes.

Using this approach makes more sense if we plan to add support for user to
include query-dependent and document-dependent features in future (we only
support query-doc dependent features at present), however these will remain
empty till the time we don't add features into them.

Regards,
Ayush