Using Arguments Other Than the First (1N)

In this first generalization of the standard indexing technique (indexing on the first argument) only one variable-free argument column in each indexing partition is used (this argument column need not be the same in all partitions).

The heuristics for finding the partitions is the following simple greedy (don't-care-choice) algorithm (1N-Algorithm):

1. For each argument column , count the number of non-variable arguments down to the first variable or the end of the procedure ()
2. 
3. If then use the first clause as a separate partition (without indexing) else
   • 
   • if then else choose with the most selective elements
   • use the first clauses as a partition and index them on the argument
4. If any clauses are left go to 1 to form further partitions else stop

Using this algorithm on the example, the following two partitions are formed:

1. • 
   • 
   • use first clause without indexing
   • go to 1 with clauses 2 - 9
2. • ,
   • 
   • 
   • use clauses 2 - 9 with indexing on argument

Resulting index tree (``/'' in else field is used here as a shortcut for a pointer to fail; arcs are directed in the natural top-to-down order):