Systems Engineering

Modular Open Systems Approach


Modular Open Systems Approach (MOSA) is an integrated business and technical strategy for the assessment and implementation of open systems in the DoD. An open system is a system that employs modular design tenets, uses widely supported and consensus-based standards for its key Interfaces, and is subject to Validation and Verification, including Test and Evaluation, to ensure the openness of its key interfaces.


An open systems design is a design approach for developing an affordable and adaptable open system. It derives inputs from both the technical management processes and technical processes undertaken within the systems engineering and other life-cycle processes, and in turn impacts these processes. The open systems design strategy should be implemented as part of the program’s overall technical approach and becomes an integral part of the program’s Systems Engineering Plan (SEP) and a summary in their Acquisition Strategy.


A key to the design of open systems is the use of open standards. The DoD Information Technology Standards Registry (DITSR) mandates the minimum set of standards and guidelines for the acquisition of all DoD systems that produce, use, or exchange information.


Programs should design their system based on adherence to the following five (5) MOSA principles:

  1. Establish an Enabling Environment: Program Manager (PM) establishes supportive requirements, business practices, and technology development, acquisition, test and evaluation, and product support strategies needed for effective development of open systems.
  2. Employ Modular Design: Effective modular design is contingent upon adherence to four major modular design tenets:
    1. Cohesive (contain well-focused and well-defined functionality)
    2. Encapsulated (hide the internal workings of a module’s behavior and its data)
    3. Self-contained (do not constrain other modules)
    4. Highly binned (use broad modular definitions to enable commonality and reuse)
  3. Designate Key Interfaces: Interfaces should be group into key and non-key interfaces. Such distinction enables designers and configuration managers to distinguish among interfaces that exist between technologically stable and volatile modules, between highly reliable and more frequently failing modules, between modules that are essential for net-centricity and those that do not perform net-centric functions, and between modules that pass vital interoperability information and those with least interoperability impact.
  4. Use Open Standards: Interface standards should be well defined, mature, widely used, and readily available.
  5. Certify Conformance: The openness of systems is verified, validated, and ensured through rigorous and well-established assessment mechanisms, well-defined interface control and management, and proactive conformance testing. The program manager, in coordination with the user, should prepare validation and verification mechanisms such as conformance certification and test plans to ensure that the system and its component modules conform to the external and internal open interface standards allowing plug-and-play of modules, net-centric information exchange, and re-configuration of mission capability in response to new threats and evolving technologies.


Open systems characteristics and principles address:

  • Design requirements (e.g., mandated open standards and protocols)
  • Derived requirements (e.g., need for open interfaces to enable interoperability)
  • Design constraints (e.g., need to adhere to open interface specifications as system components are designed)
  • Architectural attributes (e.g., need for an adaptable, upgradeable and reconfigurable system architecture)
  • Design considerations (e.g., taking into considerations modular and open systems design benefits and concerns)
  • Business strategies to gain access to competitive sources of supply and effectively manage technological obsolescence.


AcqLinks and Reference:

Updated: 8/01/2018

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