Question

Write 150 - 200 words response to the following discussion topics.

Explain four indexing techniques with suitable examples in your own words.

Answer 1

• Primary Index: in a sequentially ordered file (e.g., for a relation), the index whose search key specifies the sequential order of the file. For a relation, there can be at most one primary index. (❀ index-sequential file)

• Secondary Index: an index whose search key is different from the sequential order of the file (i.e., records in the file are not ordered according to secondary index).

• If search key does not correspond to primary key (of a relation), then multiple records can have the same search key value

• Dense Index Files: index entry appears for every search key value in the record file.

• Sparse Index Files: only index entries for some search key values are recorded.

Secondary Indexes

• Often one wants to find all records whose values in a certain field (which is not the search key of the primary index) satisfy some condition

• – Example 1: In the EMPLOYEE database, records are stored sequentially by EmpNo, we want to find employees working in a particular department.

• – Example 2: as above, but we want to find all employees with a specified salary or range of salary