Indexes can also be characterized as dense or sparse. A dense index has an index entry for the every search key value(andhence every record) in the data file. A sparse (or non dense) index on the other hand, has index entries only for some ofthe search values. A main index is hence a nondense(sparse) index, since it includes an entry for every diskblock of the data file and the keys of its anchor recordrather than for every search values(or every record).