Clustering index; Sparse index
A tree-based index is called a primary index if its order is the same as the order of the file which it indexes Consider a relation R with some numeric attribute A taking values over an (ordered) domain D. Assume that relation R has been physically stored as an ordered file, following the order of the values of attribute A. Furthermore, assume that a tree-based index (e.g., B +-tree) has been created on attribute A. Then this index is primary.
Tree-based indices are built on numeric attributes and maintain an order among the indexed search-key values. They are further categorized by whether their search-key ordering is the same with the file’s physical order (if any). Note that a file may or may not be ordered. Ordered is a file whose records are stored in pages according to the order of the values of an attribute. Obviously, a file can have at most a single such order since it is physically stored once. For example, if the Employee...