For the unconstrained version (Figure 7.3), positional indexing outperformed the non-indexed parser by an average of 21% (the best improvement being 44%). Although the difference at every sentence between the parsing times for path and positional indexing is rather variable (while the difference between parsing times for positional indexing and for non-indexed parser is almost constant), the improvements in parsing times for path indexing over the non-indexed parser are better than those of positional indexing: an average of 25%, with a maximum of 45%. However, there were no significant variations in the improvements brought by both indexing method as the parsing times increased.
When using the parsing times of the positional indexing parser as a baseline, path indexing performs better than positional indexing with an average of 5% (with a maximum of 24%). These improvements, as well as both indexing methods' improvements over the non-indexed parser, are explained by a reduction in the number of unsuccessful unifications. Some examples illustrating this reduction are presented in Table 7.1.