         )
         .attr("data-tooltip-text", (d) -> Metric.autoscale_value d.val(), 'PJ')
 
+# Pseudo-collection of nodes
+#
+class D3.mekko.NodeGroup extends Backbone.Model
+  initialize: -> @nodes = []
+  total_value: => d3.sum @nodes, (n) -> n.val()
+
+# Collection of NodeGroups
+#
 class D3.mekko.GroupCollection extends Backbone.Collection
   model: D3.mekko.NodeGroup
 
+# This collection holds all the nodes
+#
 class D3.mekko.NodeList extends Backbone.Collection
   model: D3.mekko.Node
   grand_total: => d3.sum @models, (n) -> n.val()

          color: carrier.color
          view: this

      for s in @series
        sector  = s.get('group_translated')
        carrier = s.get('label')
        @node_list.add
          sector: sector
          carrier: carrier
          gquery: s.get('gquery')
          color: s.get('color')
          view: this

        .attr("transform", "translate(30)")
        .attr("data-rel", (d) -> d.get 'key')

      # Then inside every column we create the carrier items
      #
      @sectors.selectAll(".carrier")
        .data( ((d) -> d.nodes) , ((d) -> d.key()) )
        .enter().append("svg:rect")
