DataInterface

Data interface

(methods that have been implemented will in data.gob)

For compatibility with existing code, but will eventually be unnecessary because of pipeline changes:

 * methods to get and set vartable values (from {{{vartable.c}}})

Should the signals be primarly column or row based? I think column based signals will probably be sufficient most of the time, given that most operations occur on columns.

Attribute API

The boolean values indicate whether the attribute was actually retrieved, since it is not possible to return `NULL` given that we may retrieve primitive types.