code: public ExtendedRelation addFeaturesRelationship(
  			String baseFeaturesTableName, String relatedFeaturesTableName,
  			String mappingTableName) {
  		return addRelationship(baseFeaturesTableName, relatedFeaturesTableName,
  				mappingTableName, RelationType.FEATURES);
  	}
docs: Adds a features relationship between the base feature and related feature
  table. Creates a default user mapping table if needed.
  
  @param baseFeaturesTableName
  base features table name
  @param relatedFeaturesTableName
  related features table name
  @param mappingTableName
  mapping table name
  @return The relationship that was added