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A while back we posted here about how we deal with "superlative" questions about objects with extremely high or low values of some property, like "What is the tallest mountain?". That was nice but it couldn't cope with questions with extra conditions in them, like "What is the longest river in Africa?" We've started building on this now. We've also added a few more orderings, giving us questions like "Who was the first woman to climb Everest?"
The most useful new concept seems to be the missing object class (MOC). This is a class of everything that has a particular relation to something else, for example everyone who's been president of the US, or everything that is located in France. We can improve these to get extended missing object classes, which are MOC's with an extra condition on the variables. These give us the classes like "all cities in France" and even "all cities of all republics".
An extended MOC turns the river question into "Which is the longest member of the class (river located in Africa)?" so we can answer it with all the existing machinery.
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