What is dense index and sparse index ?

What is dense index and sparse index ?

Both dense and parse indices are major types of indexes. Please note the basic properties of both:
Dense Index: An index record appears for every search key value in file.

This record contains search key value and a pointer to the actual record.
Sparse Index: Index records are created only for some of the records.
To locate a record, we find the index record with the largest search key value less than or equal to the search key value we are looking for.

We start at that record pointed to by the index record, and proceed along the pointers in the file (that is, sequentially) until we find the desired record.