Systems Engineering


A commonly recognized definition for system is "a combination of interacting elements organized to achieve one or more stated purposes" (SEVOCAB 2017).  Systems are often associated with man made items such as cars, computers, and software.  However, it is important to recognize that man made systems exist for mankind. Therefore, one involved with the design, development or support of a system should always consider the non-material (mankind) elements associated with a system. Some alternative definitions of a system include: 

  • an integrated set of elements, sub elements or assemblies that accomplish a defined objective. The elements include products (hardware, software, and firmware), processes, people, information, techniques, services and other support elements” (INCOSE 2015).
  • a complex whole the function of which depends on its parts and the interactions between these parts (Jackson 2003). 
  • a set of principles or procedures according to which something is done; an organized scheme or method.
  • A set of detailed methods, procedures and routines created to carry out a specific activity, perform a duty, or solve a problem.
  • An organized, purposeful structure that consists of interrelated and interdependent elements (components, entities, factors, members, parts etc.). These elements continually influence one another (directly or indirectly) to maintain their activity and the existence of the system, in order to achieve the goal of the system (Web Finance 2018) .

These broader definitions of a system are important when discussing systems engineering as the systems engineer must establish a holistic view of the user and the user's environment in order to deliver and sustain useful systems.

A System of Interest (SOI) is the system or arrangement of systems that is the subject of an analytic or engineering endeavor (SE VOCAB).

Systems Engineering

A holistic systems view to solving problems traces as far back as the 1930s when the British defense ministry used operations research techniques to develop strategies for air defense (INFORMS 2016).

INFORMS: Institute for Operations Research and Management Sciences is the Community of Practice for Operations Research and Analysis

INCOSE defines systems engineering as an interdisciplinary approach and means to enable the realization of successful systems. Systems engineering (SE) is more than designing a solution. SE involves the exploration of the organization and its business or mission space. SE includes the identification of the strategic objectives and challenges of the organization and the potential courses of action to satisfy the organization’s needs. An SE effort considers the social, economic, financial business and technical aspects of the organization and then guides a solution design and development that balances these factors (INCOSE 2016).

Initially, the application of SE to projects focused on large defense and space projects. Today, SE is a mature discipline practiced by engineers across the private and government sectors (INCOSE 2016).

See Technology in National Defense for more on the DoD's Role in Technology Development

As the DOD of the past drove technology development, it also had a strong influence in the methods and practices followed by its systems engineering practitioners. This DOD leadership paradigm existed because the motivation to practice systems engineering was initially limited to large DOD and space programs (INCOSE 2016).

The Defense Acquisition System (DAS) is the framework by which acquisition of U.S. military capabilities are developed, supported and sustained. The Defense Acquisition Guide (DAG) is the capstone publication for the DAS and promulgated as DOD Instruction 5000 (DAU 2015). Early versions of this instruction focused on large scale weapon systems in which time from inception to delivery could exceed 10 years or more. Therefore, the systems engineering structure, processes and techniques were very DOD centric (USD AT&L 2015)

The civilian sector’s increase in complex technical investments to gain market advantage elevated the appreciation by corporate leaders for disciplined SE for software and system development. Several industry groups composed of the practitioners from both the DOD and industry began to establish frameworks and best practices as means to mature the practices of systems engineering and software development (INCOSE 2011).

See Professional Organizations for the current CABoK list of organizations

Two frequently referenced organizations are the International Organization for Standardization, which operates under the ISO brand, and the International Council on Systems Engineering (INCOSE). The International Organization for Standards and INCOSE are both independent, nonprofit organizations and both have the common goal of increased predictability of success through common frameworks and standards. Starting as a civil engineering organization, ISO now covers a broad view of the industrial system with 21,000 industrial standards. The ISO Standard 15228 for systems and software engineering initially released in 2002 and was updated in 2008 and again in 2015 (ISO 2016). The system life cycle processes within 15228:2008 and 15228:2015 are widely recognized as the core elements of a systems engineering framework. Where ISO is a standards organization that has published SE standards INCOSE is a professional community of practice whose mission is to advance the state of the SE practice through the adoption of common engineering practices and techniques.

INCOSE publishes its Systems Engineering Handbook that uses the ISO 15228: standard as the lexicon to describe its recommended systems engineering practices. The 2015 release of the INCOSE Systems Engineering Handbook reflects the changes to the SE process areas in the ISO 15228:2015 standard. The ISO specification defines the activities that constitute a recognized systems engineering process. The INCOSE handbook provides amplifying information on how the processes apply to an engineering project along with a set of recommended sub-activities for each of the ISO defined activities (INCOSE 2011). Recognizing the need to align with and leverage the generally accepted practices of industry, DOD began its alignment to open standards in the early 2000s. The DAG provides the DOD definition of its SE processes and the application of these processes in defense programs. Recent updates to the systems engineering section of the DAG now use terms and activities consistent with that of ISO 15288:2008. Since the ISO 2015 update, the exact names of the activities are slightly discordant between the DOD SE document and the private sector SE documents. The consistency in SE approach between the two documents remains. A consistency in terms and definitions between DOD and private sector reduces the learning curve for practitioners who move between the two domains. The relationship between these publications is that ISO and the DAG define the common terms and activities while the INCOSE handbook uses the same lexicon as ISO to provide guidance on how to apply system engineering to a project (Defense Acquisition University 2015; INCOSE 2011; INCOSE 2015).

Please read Systems Engineering as defined by ISO/IEC/IEEE 15288:2015 for more information about the processes defined by 15288:2015.

Standard 15288:2015 was published under a joint agreement of ISO, the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) and is managed by ISO.

Figure 1 provides a graphic representation of the elements  and organizations associated with a systems engineering endeavor as described in 15288:2015. The principle organizations are that of the parties requiring a new capability (left box in the diagram) and those who provide the new capability (the bottom box) through application of systems engineering processes .  The center box represents the systems engineering project and its activities which results in a new capability represented in the right side of the diagram.  15288:2015 provides the common language and process framework that enable the organizations to effectively plan, execute, monitor and communicate within the project environment.  By adopting 15288:2015 as the guiding structure for an SE endeavor the performing organization benefits from an established process lexicon and the ability to communicate externally to the acquiring and supporting organizations.


The processes in 15288:2015 are divided into four  groups: Technical, Technical Management, Agreement and Organizational Project-enabling.  Figure 3 depicts these process groups and Figure 4 depicts the processes associated within each of the groups. Looking back to Figure 1, the Technical, Technical Management and Agreement Processes are executed during the SE endeavor (center box). The technical processes are the activities directly associated with the definition, design, development, delivery and support of the system while the technical management processes are those executed by the project team to manage the endeavor, its information, and the components that result in a new or revised system.  The Agreement processes describe how the systems engineering IPT is to acquire goods and services external to the IPT as well as to establish the cost, schedule and cost criteria with the acquiring organization. These processes should be consistent with the organization's standard processes shown in the in the bottom box of Figure 1.
The Organizational Project Enabling Process Area, as shown in the bottom box of Figure 1, describes the methods performed by the IPT's parent organization to establish and maintain mechanisms to support all projects executed by the organization.    The activities required to develop, maintain and promulgate the the standard processes is performed by the performing organization and are typically managed by a group external to the individual SE projects the organization executes.


More information about SE and SE processes can be found:

The Systems Life Cycle: Systems Life Cycle

Systems Engineering Processes: Systems Engineering as defined by ISO/IEC/IEEE 15288:2015

International Council on Systems Engineering: INCOSE

INCOSE Systems Engineering Handbook: INCOSE Systems Engineering Handbook


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