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Posting resolution

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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