====== Baseline Immutability ======

[[dido:99_annexes:annex-b-terms-and-definitions:start|Go to Terms and Definitions]]

===== Discussion =====

Baseline Immutability is the characteristic of an identified [[dido:99_annexes:annex-b-terms-and-definitions:b:baseline|Baseline]] Revision whose content cannot be modified after the Revision enters the state governed by the applicable immutability rule.

The applicable rule may establish immutability when the Baseline Revision is:

  * Approved
  * Released
  * Published
  * Selected for deployment
  * Used to create an operational subject
  * Recorded as an authoritative reference
  * Associated with generated [[dido:99_annexes:annex-b-terms-and-definitions:e:evidence|Evidence]]

Baseline Immutability preserves the exact content associated with an identified Baseline Revision.

A required change does not modify the immutable Baseline Revision. The change produces a new [[dido:99_annexes:annex-b-terms-and-definitions:r:revision|Revision]] with its own identifier.

Baseline Immutability differs from access control:

  * Access control determines who may perform an operation
  * Baseline Immutability prohibits modification of the governed Baseline Revision regardless of ordinary modification permission

Baseline Immutability also differs from Baseline stability:

  * Baseline Immutability prevents modification of an identified Revision
  * Baseline stability concerns the frequency or significance of change across successive Revisions

===== Definition =====

//immutability of an identified baseline revision that prevents modification of its content after the revision enters a defined controlled state//

===== Source =====

Dido Solutions, Inc. and Jackrabbit Consulting, Inc.

===== Note =====

Baseline Immutability does not prohibit creation of a succeeding Baseline Revision.

An immutable Baseline Revision may still be:

  * Retrieved
  * Read
  * Compared
  * Selected
  * Reused
  * Superseded
  * Retired
  * Archived

The applicable requirements determine:

  * The state that activates immutability
  * The content protected by immutability
  * Permitted metadata changes
  * The mechanism used to verify immutability
  * The retention period
  * The process for creating a succeeding Revision

===== Example =====

After approval, a Security Baseline Revision cannot be modified. A required control change produces a new Security Baseline Revision while the approved earlier Revision remains unchanged and retrievable.

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