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This section will present a formal description of file structures
...Basic terminology Given a set of attributes A and a set of values V,then a record R is a subset of the cartesian product A x V in which each attribute has one and only one value
...R K 1,x 1,K 2,x 2,...The Ki s are keywords functioning as attributes and the value xi can be thought of as a numerical weight
...R Kt 1,Kt 2,...where Kti i s present if xti 1 and is absent otherwise
...Records are collected into logical units called files
...It is difficult in describing file structures to keep the logical features separate from the physical ones
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