spec.IMicColumn interface describes a MIC column's structured specification.
This interface is used to form a
| attr :
The name of an attribute playing the "crossed-measure" role.
When there is a single measure attribute, the default value is its name.
The specification is invalid when the attribute is not specified and there is more than one measure attribute.
| c :
An array of cell specifications.
These cells form a tuple that identifies the column's entity set. Its structure must be that of the attributes playing the "crossed-column" role, as specified in the table's layout,
See also: pentaho.data.spec.MicColumn