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Typically we need only keep track of {which } document contains the
posting. But an important element of many query languages are
PROXIMITY operators which allow users to specify how close two
keywords must be (adjacent words, within the same sentence, within the
same paragraph, within a $k$-word window of one another, etc.). To
support such queries, we may also be concerned with recording higher
RESOLUTION posting information than just which document it is in.
For example, many systems retain the exact {\em character} position of
the (beginning of the) keyword. Figure (figure) shows the
elaborate data structure used by the STAIRS IR system. In addition to
very high-resolution postings, this representation supported other query
attributes (e.g. security) as well.
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Posting resolution