Indexes provide secondary access paths to speed up record retrieval in response to search conditions. There are different types of single-level ordered indexes like primary, clustering, and secondary indexes. Multi-level indexes can also be constructed to improve search efficiency by splitting large indexes into multiple levels of smaller indexes. Common dynamic multi-level indexes used are B-trees and B+-trees, which allow efficient search, insertion, and deletion operations. Indexes can be built on single or multiple fields to support different access patterns.

1. CHAPTER 6 Index Structures for Files

3. INDEX – consists of keys and addresses (physical disc locations.

6. Adams, John Aaron, Ed Alexander, Ed Aaron, Ed Acosta, Marc Abbott, Diane (Primary key field) NAME DATA FILE SSN BLOCK ANCHOR PRIMARY KEY VALUE BLOCK POINTER BDATE JOB SALARY INDEX FILE (<K(i), P(i)>entries) Adams, John Adams, Robin Alexander, Ed Alfred, Bob Akers, John Allen, Sam PRIMARY INDEX

8. DENSE INDEX

9. SPARSE OR NON-DENSE INDEX

12. CLUSTERING INDEX

14. SECONDARY INDEX

15. TYPES OF INDEXES ORDERING FIELD NON ORDERING FIELD Key field NonKey field Primary index Secondary index (nonkey) Secondary index (key) Clustering index

16. PROPERTIES OF INDEX TYPES No Dense or nondense Number of records or number of distinct index field values Secondary (nonkey) No Dense Number of records in data file Secondary (key) Yes/No Nondense Number of distinct index field values Clustering Yes Nondense Number of blocks in data file Primary BLOCK ANCHORING ON THE DATA FILE DENSE OR NONDENSE NUMBER OF (FIRST-LEVEL) INDEX ENTRIES TYPE OF INDEX

18. MULTILEVEL INDEX 5 3000 4 2500 3 2000 2 1500 1 1000 Address(Index) High Key 14 2500 13 2400 12 2300 11 2200 10 2100 Address(Index) High Key 69 2400 68 2390 67 2380 66 2370 65 2360 64 2350 63 2340 62 2330 61 2320 60 2310 Address(Index) High Key 781049 2360 781048 2359 781047 2358 781046 2357 781045 2356 781044 2355 781043 2354 781042 2353 781041 2352 781040 2351 Address Key

23. A K I H G D C J F E B Root node (level 0) nodes at level 1 Nodes at level 2 Nodes at level 3 SUBTREE FOR NODE B (nodes E, J, C, G, H, and K are leaf nodes of the tree) A tree data structure that shows an unbalanced tree.

27. A simple B tree example.

29. A simple B+ tree example linking the keys 1-7 to data values d1-d7. Note the linked list (red) allowing rapid in-order traversal.