Test Case 3: ATIS - A medium size NL grammar

We used a modified version of the ATIS grammar and test inputs generated
by Carroll (2003), who extracted them from the DARPA ATIS3 treebank.
Our modifications include adding 634 new rules and 66 new nonterminals in
order to encode the ATIS lexicon as CFG rules.

The resulting grammar consists of 5,226 rules with 258 nonterminals and
991 terminals. Carroll's test input set contains 98 natural language sentences
of average length 11.4 words.

Times to parse ranged from <1 second for the 5 shortest inputs, to between
12 and 19 seconds for the 5 longest inputs. The average time was 1.88 seconds.