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When Watson receives a
question, the first step

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is question analysis.

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One of the things Watson tries
to figure out in this step

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is what the question
is looking for.

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This is defined as trying
to find the Lexical Answer

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Type, or LAT, of the question.

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The LAT is the word or
noun in the question

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that specifies the
type of answer.

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You should be able to replace
the LAT with the answer

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to complete the sentence.

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For example, for the
question, "Mozart's last

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and perhaps most
powerful symphony

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shares its name with this
planet," the LAT in this case

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is "this planet."

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If we replace this with
the answer "Jupiter,"

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it makes sense.

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Mozart's last and perhaps
most powerful symphony shares

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its name with Jupiter.

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For the question, "Smaller
than only Greenland,

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it's the world's second largest
island," the LAT is "it's."

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If we replace the LAT with
the answer "New Guinea,"

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it makes sense.

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"Smaller than only
Greenland, New Guinea

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is the world's second
largest island."

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Unfortunately, the
LAT is not "island,"

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which would be more descriptive,
since the sentence with "New

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Guinea" in place of "island"
does not make sense.

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We can see in these two examples
that sometimes the LAT is very

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specific, like "this planet,"
and sometimes it's very vague,

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like "it's."

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If we know the LAT, we
know what to look for.

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However, in an analysis
of 20,000 questions,

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2,500 distinct LATs were
found, and 12% of the questions

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did not even have
an explicit LAT.

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They had LATs like "it's."

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Furthermore, even the most
frequent 200 explicit LATs

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cover less than 50%
of the questions.

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So to enhance the
question analysis step,

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Watson also performs
relation detection

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to find relationships among
words and decomposition

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to split the question
into different clues.

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The second step in Watson
is hypothesis generation.

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The goal of this step is to use
the question analysis of step

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one to produce candidate answers
by searching the databases.

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In this step several
hundred candidate answers

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are generated.

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For the question, "Mozart's
last and perhaps most powerful

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symphony shares its
name with this planet,"

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candidate answers could be
Mercury, Earth, and Jupiter.

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These are generated using
various search techniques.

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Then each candidate
answer plugged back

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into the question
in place of the LAT

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is considered a hypothesis.

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For the question about
Mozart's symphony,

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hypothesis one would
be the question

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with "Mercury" in
place of "this planet."

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Hypothesis two
would have "Jupiter"

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in place of "this planet."

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And hypothesis three
would have "Earth"

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in place of "this planet."

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If the correct answer is
not generated at this stage,

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Watson has no hope of
getting the question right.

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Therefore, this step
errors on the side

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of generating a
lot of hypotheses

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and leaves it up
to the next step

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to find the correct answer.

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In the next video, we'll
discuss how steps three and four

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score and rank the hypotheses.