The key factor in the WSC is the special format of its questions, which are derived from Winograd schemas. Questions of this form may be tailored to require knowledge and commonsense reasoning in a variety of domains. They must also be carefully written not to betray their answers by
selectional restrictions or statistical information about the words in the sentence.
Origin The first cited example of a Winograd schema (and the reason for their name) is due to
Terry Winograd: The choices of "feared" and "advocated" turn the schema into its two instances: The schema challenge question is, "Does the pronoun 'they' refer to the city councilmen or the demonstrators?" Switching between the two instances of the schema changes the answer. The answer is immediate for a human reader, but proves difficult to emulate in machines. Levesque
Formal description A Winograd schema challenge question consists of three parts: • A sentence or brief discourse that contains the following: • Two
noun phrases of the same
semantic class (male, female, inanimate, or group of objects or people), • An ambiguous
pronoun that may refer to either of the above noun phrases, and • A special word and alternate word, such that if the special word is replaced with the alternate word, the natural resolution of the pronoun changes. • A question asking the identity of the ambiguous pronoun, and • Two answer choices corresponding to the noun phrases in question. A machine will be given the problem in a standardized form which includes the answer choices, thus making it a
binary decision problem.
Advantages The Winograd schema challenge has the following purported advantages: • Knowledge and commonsense reasoning are required to solve them. • Winograd schemas of varying difficulty may be designed, involving anything from simple cause-and-effect relationships to complex narratives of events. • They may be constructed to test reasoning ability in specific domains (e.g., social/psychological or spatial reasoning). • There is no need for human judges.
Pitfalls One difficulty with the Winograd schema challenge is the development of the questions. They need to be carefully tailored to ensure that they require commonsense reasoning to solve. For example, Levesque gives the following example of a so-called Winograd schema that is "too easy": The answer to this question can be determined on the basis of
selectional restrictions: in any situation, pills do not get pregnant, women do; women cannot be carcinogenic, but pills can. Thus this answer could be derived without the use of reasoning, or any understanding of the sentences' meaning—all that is necessary is data on the selectional restrictions of
pregnant and
carcinogenic. == Activity ==