Editing Virtual Storage Access Method (section)

===Indexed organization===
{{further|key-sequenced data set}}
A KSDS has two parts: the index component and the data component. These may be stored on separate disk volumes.

While a basic KSDS only has one key (the primary key), alternate indices may be defined to permit the use of additional fields as secondary keys. An alternate index (AIX) is itself a KSDS.

The data structure used by a KSDS is nowadays known as a [[B+ tree]].<ref>{{cite web
   |url=https://patents.justia.com/patent/9043295
   |title=US Patent for Providing record-level alternate-index upgrade locking}}</ref><ref>{{cite web
|url=https://www.wisegeek.com/what-is-vsam.htm
|quote=This index is called a B+ tree.
|title=What is VSAM?}}</ref>