SA-8(4)—Security and Privacy Engineering Principles | Partially Ordered Dependencies
>Control Description
>DoD Impact Level Requirements
No specific parameter values or requirements for this impact level.
>Discussion
The principle of partially ordered dependencies states that the synchronization, calling, and other dependencies in the system are partially ordered. A fundamental concept in system design is layering, whereby the system is organized into well-defined, functionally related modules or components. The layers are linearly ordered with respect to inter-layer dependencies, such that higher layers are dependent on lower layers.
While providing functionality to higher layers, some layers can be self-contained and not dependent on lower layers. While a partial ordering of all functions in a given system may not be possible, if circular dependencies are constrained to occur within layers, the inherent problems of circularity can be more easily managed. Partially ordered dependencies and system layering contribute significantly to the simplicity and coherency of the system design.
Partially ordered dependencies also facilitate system testing and analysis.
>Assessment Interview Topics
Questions assessors commonly ask
Process & Governance:
- •What acquisition policies and procedures address the requirements of SA-8(4)?
- •How are security and privacy requirements integrated into the acquisition process?
- •Who is responsible for ensuring that acquisitions comply with SA-8(4)?
Technical Implementation:
- •How are security requirements defined and documented in acquisition contracts?
- •What mechanisms ensure that acquired systems and services meet security requirements?
- •How do you validate that vendors and service providers comply with specified security controls?
Evidence & Documentation:
- •Can you provide examples of acquisition documentation that includes security requirements?
- •What evidence demonstrates that acquired systems meet security specifications?
- •Where is acquisition security documentation maintained throughout the system lifecycle?
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