The indexing mechanism that we have introduced could be seen as a generalization of the Chart or tabular approaches developed in the area of parsing algorithms but now also available for generation. Since we use the value of the essential feature, the indices of all item sets together simulate a kind of input traversal. For example, if the grammar describes a left-to-right concatenation of strings, then the indices describe the left-to-right traversal of the string, so that the index of a ``right'' item set is a proper substring of the index of a ``left'' item set. In the case of generation, the indices can be viewed as being constructed by a means of predicate/argument traversal. Since, we view a predicate/argument construction structurally as a tree, generation realizes a kind of tree traversal.