SECTION 3.3. A BENEFIT, SINCE IT GIVES MORE OPPORTUNITY FOR ENFORC-

2002), answer types in QA systems typically corre-

the usefulness of the entire approach.

spond to the types identifiable by their named-entity

recognizer (NER). There is no agreed-upon number

As a consequence, we have identified the need for a

of classes for an NER system, even approximately.

component whose sole purpose is to establish the

It turns out that for best coverage by our

equivalence, or generally the kind of relationship,

C

M

, it is advantageous to have a

between two terms. It is clear that the processing

relatively large number of types. It was mentioned

will be very type-dependent – for example, if two

in Section 4.2 that certain questions were not invert-

populations are being compared, then a numerical

ible because no terms in them were of a recogniz-

difference of 5% (say) might not be considered a

able type. Even when questions did have typed

difference at all; for “Where” questions, there are

terms, if the types were very high-level then creating

issues of granularity and physical proximity, and so

a meaningful inverted question was problematic.

on. More examples of this problem were given in

For example, for QA without Constraints it is not

(Prager et al. 2004a). Moriceau (2006) reports a

necessary to know the type of “MTV” in “When

system that addresses part of this problem by trying

was MTV started?”, but if it is only known to be a

to rationalize different but “similar” answers to the

Name then the inverted question “What <Name>

user, but does not extend to a general-purpose

was started in 1980?” could be too general to be ef-

equivalence identifier.

fective.

6 Summary