lecture1-intro-handout-6-per

Gthisslidehasdisnctlyidenedzonessuchas

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Unformatted text preview: orma)on Retrieval Sec. 1.3 Query
op)miza)on
example
 More
general
op)miza)on
   Process
in
order
of
increasing
freq:
   e.g.,
(madding OR crowd) AND (ignoble OR strife)
   Get
doc.
freq.’s
for
all
terms.
   Es)mate
the
size
of
each
OR
by
the
sum
of
its
 doc.
freq.’s
(conserva)ve).
   Process
in
increasing
order
of
OR
sizes.
   start with smallest set, then keep cuEng further.
 This is why we kept document freq. in dictionary 2 Brutus Caesar Calpurnia 4 1 2 8 16 32 64 128 3 5 8 16 21 34 13 16 Execute
the
query
as
(Calpurnia
AND
Brutus)
AND Caesar.
 31
 Introduc)on to Informa)on Retrieval 32
 Introduc)on to Informa)on Retrieval Exercise
 Query
processing
exercises
   Exercise:
If
the
query
is
friends
AND romans AND (NOT countrymen), how
could
we
use
the
freq
of
 countrymen?
   Exercise:
Extend
the
merge
to
an
arbitrary
Boolean
 query.

Can
we
always
guarantee
execu)on
in
)me
 linear
in
the
total
pos)ngs
size?
   Hint:
Begin
with
the
case
of
a
Boolean
formula
query
 where
each
term
appears
only
once
in
the
query.
   Recommend
a
query
 processing
order
for
 (tangerine OR trees) AND (marmalade OR skies) AND (kaleidoscope OR eyes) 33
 Introduc)...
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