In this approach, the pattern-matching that is allowed is restricted to certain semantic categories. A grammar is used to specify the allowable patterns; this allows the restrictions to be specified easily, while allowing more language coverage and easier extension with fewer specified patterns.
< s> --> what is < ship-property> of < ship> ? < ship-property> --> the < ship-prop> | < ship-prop> < ship-prop> --> speed | length | draft | beam < ship> --> < ship-name> | the fastest < ship2> | the biggest < ship2> | < ship2> < ship-name> | Kennedy | Kitty Hawk | Constellation < ship2> --> < countrys> < ship3> | < ship3> < ship3> --> < shiptype> < loc> | < shiptype> < shiptype> --> carrier | submarine | ... < countrys> --> American | French | British < loc> --> in the Mediterranean | in the Med | ...
"What is the length of the biggest French sub in the Med?"
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