This lexicon is intended as a handy reference for common and some not so common systems engineering terms. Program Managers, Project Leaders, Systems Engineers and others who interact with these professionals are encouraged to read and critique the proposed definitions and guidance. The idea is to develop terminology with which professionals in the field of systems engineering might reach consensus. Anyone so moved should feel free to contribute alternative text, other terms, and supporting material on this site.

In part, the original terminology presented here has been derived from various definitions of the same terms provided by others. In the interest of brevity, alternative definitions, characteristics, or examples of the defined terms, all supported by selected references, are offered elsewhere; contact the author, Dr. Brian E. White, Director of The MITRE Corporation's Systems Engineering Process Office (SEPO), bewhite@mitre.org; phone (781) 271-8218; cell: (617) 893-9542, for more detail. E-mail Dr. White anytime day or night, but please call only during business hours.

The principal point of contact for any issues concerning this Web site is the Publisher, Rich O'Hanley at Taylor & Francis.

"lexicon - 1. the vocabulary of a person, language, or branch of knowledge."
[The Oxford American College Dictionary, G. P. Putnam's Sons, New York, 2002, Oxford University Press]

Executive Summary
What's in a word? Terminology is crucial to understanding what, for example, "enterprise systems engineering" and related words mean. Many terms are in use to define approximately the same thing.

Preference is given to human or human-made entities or qualities, as opposed to natural entities or qualities, because the focus here is on human experience as opposed to the purely natural. Natural entities or qualities may be included as part of but not the whole (e.g., "complex") system being discussed, however.

A Continuum of Systems Engineering
Some license is taken in this lexicon to emphasize differences among different forms of systems engineering that have been labeled traditional, system-of-system, enterprise, and complex systems engineering. Although this has been done intentionally to highlight some distinctions to be made, one should always keep in mind that systems engineering is more of a continuum than a set of distinct disciplines. An attempt to describe this continuum is provided in the figure below. Nine generic activities of systems engineering are proposed on the left. These activities are not independent and they do not necessarily occur in the order shown, although arguably they do follow a logical ordering.

A "slider" bar is associated with each activity. The intent is to allow one to characterize the nature of their participation in each systems engineering activity by positioning the "sliders" (the small yellow rectangles) on the slider bars. Descriptions of the five "waypoints" (at each end and at three intermediate points of each slider) are offered to help a person decide where to place each slider. Again, these descriptions should be considered draft; improved phraseology is welcome.

Once the nine sliders are placed and their interconnections are made (an optional step as shown by the yellow rectangles/lines pattern), an overall assessment of where one is on the systems engineering continuum (shown at the bottom of the figure) can be made. The labels at each end of this continuum, Traditional Systems Engineering (TSE) and Complex Systems Engineering (CSE) are introduced for convenience. To the extent these labels are objectionable one should reinterpret them as seen fit and suggest or use alternative terminology.

Again, the intent here is to be helpful, not pejorative, so one should contemplate these definitions and the slider chart with a healthy dose of skepticism, and feel free to suggest improvements. Discussion about the underlying concepts that leads to collaborative actions for improving the practice of systems engineering is what is most important.

Lexicon Organization
We offer here, for consideration, in alphabetical order, concise definitions of bolded terms of potential interest. If terms defined elsewhere in this lexicon are used in a definition, these are bolded as well. Also, a term closely related to the term currently being defined may be cited and bolded. For ease of navigating this lexicon, there is a link associated with all bolded terms within a definition. A definition also may be amplified with some associated Features as well as appended explanatory Note.

Links to other sources are offered liberally for those that want to learn more about certain terms. A glossary of acronyms is provided at the end of the lexicon.

When the terms are considered in a logical order, where a given term is defined before being used in a subsequent definition, the relationships among the definitions should be considered according to relationships demonstrated below in the following two diagrams. Here a term on the right depends on terms to its left.

A

Accuracy An indication of the degree of approximation to a true underlying value. See precision.

Acquisition The business of developing and fielding systems for government agencies. This term is usually applied after the government customer has conceived of capabilities needs, has some idea of a potential solution, and has established a program office. The acquisition process normally starts with the preparation of a request for information (RFI) or request for proposal (RFP). There is then a source selection, contract award, a development phase, engineering and management phase, and a testing phase. Acquisition ends with fielding; that is when the sustainment (logistical support) phase begins. For more information, see

• AT&L Knowledge Sharing System
• AcqWeb
• General Services Administration
• Federal Acquisition Institute
• Defense Acquisition University

Agent 1. Autonomous: independent, intelligent actor, often human, that primarily pursues its own agenda, governed largely by self-interest; 2 Autonomic: robotic, preprogrammed automaton or non-human actor whose actions are deterministic but cannot always be predicted because of the intricacy of its programs. For more information on agent-based modeling, see the Project Albert Web site.

Aggregation An accumulation or collection of entities or results at one particular scale/view.

Allocation 1. Specification of promised or provided resources, e.g., staff time or funding, to an approved activity. 2. Assignment of list items, e.g., problems or actions, to categories or persons.

Analysis An examination of something (an entity or an idea) that is (vice what could be), using scientific principles, presented from one or more points of view with the objective of making greater sense out of the perceived situation. See synthesis.

Approximation An estimated quantity, sufficiently accurate to provide a satisfactory answer or useful calibration of an entity so that other dependent activities can proceed. See accuracy.

Architecture The fundamental organization or structure of a system characterizing the relationships among its components, their relationship to the environment, and the principles guiding the system's design and evolution. For more information, see

• Guide to the Enterprise Architecture Body of Knowledge
• Federal Enterprise Architecture site
• INCOSE Systems Architecture Tools Survey

Attributes Properties or pattern characteristics that highlight what is deemed to be of interest or use at one or more views.

Availability 1. Percentage of a specified interval during which a given system performs at full intended capabilities. 2. Likelihood that an intended user can access a given system successfully.

B

Balance A term describing a desirable condition fostering an overall effectiveness and robustness that is (or can be) met by the whole system, considering the competing and cooperating demands of all its subsystems or components, and their relationships. This is usually considered from a global (as opposed to local) perspective. See optimum.

Note: Arguably, balance is especially important in complex systems engineering because optimizations typically are more difficult to achieve in that environment.

Baseline A system configuration and its characteristics, parameters, and performance, established as a reference against which future measurements or proposed configurations can be compared.

Note: Baselines can be used to monitor for degradation or to compare with future improvements.

Basics Fundamental aspects of a subject worth highlighting, especially for those not familiar with it. For more information, see the INCOSE SE Primer.

Behavior Actions of a given entity or collection of entities which can be recorded or registered by another entity, e.g., observed by a human, and subsequently measured, critiqued or used in other ways.

Benefits Good things that may accrue through pursuit of a plan of action or operation of a given entity. See basics.

Biology The science of living things, especially as it informs complex systems engineering.

Block 1. A collection of subsystem capabilities implemented or fielded together during an acquisition process; 2. The act of preventing, or something that acts to prevent future possibilities.

Bullet 1. A typographical symbol used to demarcate something; e.g., a list, statement, phrase, or other item in a textual document or chart. 2. Ammunition used in a firearm.

C

Capabilities: What users really want their operations to achieve; currently more in vogue than requirements (which tend to be more specific and change more frequently) and are akin to outcome spaces rather than outcomes. See requirements. For more information, see

• Carnegie Mellon Software Engineering Institute CMMI Home Page
• Defense Acquisition Policy Center (for policies on JCIDS and Capabilities-Based Acquisition)
• INCOSE SE Capability Assessment Model.

Centralized A form of organization, e.g., network structure, often associated with a control hierarchy working from a sort of hub that can be considered the opposite of distributed.

Certification An authoritative statement of assurance attesting that a such an entity, e.g., architecture, system, equipment, organization, or individual, possesses certain capabilities of value that have been determined, usually by a body of experts knowledgeable in the matter to be certified.

Chaos A state of being that is out of control with no apparent underlying explanation.

Note: Control is not achievable practically because of the inability to know initial conditions with sufficient accuracy, even if the "embedded rules" that might described the "operation" of the entity that we view as in chaos, were known and most often they're not.

Characteristics Properties or patterns that may be used to distinguish objects or ideas. See attributes.

Closed Self-contained with no opportunity for interactions with what is considered the "external environment." See open and complex system.

Cognition The human ability to perceive, be aware of, and understand the world to a greater or lesser degree.

Note: This awareness can be conscious as well as subconscious (often simultaneously) and is potentially beneficial or detrimental to one's well being.

Complex Adaptive System (CAS) A term that is often used interchangeably with complex system.

Notes: Many define a complex adaptive system in terms of a system, not a complex system. A complex system follows a process of evolution the meaning of which is not fully conveyed by the "adaptive" qualifier.

Complex System An open system with continually cooperating and competing elements. See enterprise.

Features: This type of system continually evolves and changes its behavior, often in unexpected ways, according to its own condition and external environment. Changes between states of order and chaotic flux are possible. Relationships among its elements are imperfectly known and are difficult to describe, understand, predict, manage, control, design, or change.

Notes: This suggests examining the role of a system's boundary in differentiating between open and closed. A closed system is merely a system that has been defined with respect to a boundary that contains the totality of its interactions. Inside that boundary, that same system might look "open". On the other hand, even an open system has a boundary, or else there would be no "external" to define or identify the system. Defining the bounds of a system is a critical early step in any good systems engineering process. It is sometimes possible to make the system open or closed by appropriately defining the boundary. A complex system is not merely complicated. It is nonlinear, and chaotic behavior can be an intrinsic property of the system that connotes the sensitivity of the system to perturbations of the initial conditions. Also, when such a system is given inputs from an aggregation of random processes, the result appears complex; a system that is predominately linear can be predictable, even if the inputs are random. A complex system is not necessarily an enterprise.

Complex Systems Engineering (CSE) Enterprise systems engineering that includes conscious attempts to further open an enterprise in order to create a less stable equilibrium among its interdependent component systems. See complex system and emergence. For more information, see the paper, Engineering Complex Systems.

Features: In CSE, critical attention is paid to emergence of phenomena or conditions in the system that could be desirable or not, especially because of the tendency for complex systems to become more open. Thus, it is important to attempt to manage as quickly (beware of unexpected consequences that may emerge after some time delay) and deliberately as possible, the natural processes that shape the development of complex systems.

Notes: For some a better working definition might be Systems Engineering that attempts to exploit complexity, and control or manage the results of complexity. Neither "open" nor "closed" is a determinant of complex or emergent behavior.

Complexity A technical term qualitatively describing the ultimate richness of an entity that 1) continuously evolves dynamically by organizing its own internal relationships and interacting with its environment; 2) requires multi-view analysis to perceive different non-repeating patterns of its behavior; and 3) defies methods of pre-specification, prediction, and control. See variation and selection.

Features: Complex entities possess attributes which cause them to evolve naturally without outside intervention. It is also not possible to pre-specify or predict completely and accurately what will happen with complex entities, even when one intervenes from the outside (or especially from within as an autonomous agent) with a specific purpose. The attribute of complexity is usually associated with the property of instability. Furthermore, it isn't possible to replicate complexity exactly. Each instance of a complex entity is unique. Increasing a system's complexity implies its potential behavior will display more variety, nuance, and depth. A system can become so complex that its state approaches that of chaos-and may even transition into chaos-making its nature even more difficult to understand. A system might also evolve with diminishing complexity, trending toward stability. This trend may continue to the point that the system approaches stasis and may even transition into stasis where it might be described as deficient in variety and richness, uninteresting, possibly stagnant, or even boring. Here stasis means rigid, inflexible, unchanging, etc. The challenge of CSE is to attempt to shape the environment of a complex system by continually introducing variety and selection (akin to W. Ross Ashby's "Law of Requisite Variety", introduced in Chapter 11 of Introduction to Cybernetics, 1956, University Paperbacks, June 1964). This enables a system to become even more complex, yet avoid chaos or stasis.

Notes: Many people use the term "complex" as a synonym for anything that is complicated and difficult for a typical human being to understand. Although this is often appropriate in the English vernacular, when used in the context of ESE the term "complexity" implies discerning the matter being considered in much greater depth. Like SE, complexity can be thought of as a continuum, with "complicated" at the least complex end of the scale.

Concept An abstract idea.

Note: Before it can be usefully applied or put into practice in context, a concept needs to be developed.

Configuration A traditional systems engineering (TSE) term used to describe and distinguish the state of a system, or subsystem, e.g., a software program, or acquisition development from all of its other states.

Note: Here "state" means whatever information or representation is deemed necessary to provide a particular characterization of the entity being configured.

Concept of Operations (CONOPS) A vision of how users or developers will interact with a system under the conditions for which it was designed.

Constraints Conditions, policies, or unplanned/unexpected environmental circumstances that impede an entity's freedom.

Note: Such circumstances can be imposed by a system, enterprise, organization, or person.

Constructionism The practice of assembling a system from its constituent parts with the expectation that the behavior of the system will reflect only the prescribed and implied system functionality of the interconnected parts. See reductionism.

Control The ability to directly determine, change, or at least influence, the behavior of another entity, e.g., a person, or the state or underlying structure or design of a system.

Note: Control is a function of power.

Convergence Migration of various entities or technologies, sometimes operating under different conditions, in order to facilitate greater interoperability among them.

Critical Path Method (CPM) A traditional systems engineering (TSE) technique to help achieve an acquisition objective by determining and prioritizing the most effective confluence of schedule, cost, and performance tasks.

D

Data Formalized object representations in different forms or media suitable for communication, processing, and interpretation by machines or humans; the raw material of information.

Decision The act of selecting one alternative from among more than one option. For more information, see MITRE’s Decision Support Technology Area Team (TAT).

Decomposition The information-lossless partitioning of an entity into composite parts.

Derivation The results of a procedure leading logically from one situation to another.

Design A collection of creative purposeful actions involving the arrangement of material or ideas that is intended to lead to a useful result.

Development A major phase of the system acquisition process, generally preceding the engineering management, testing, and fielding phases.

Development Test and Evaluation (DT&E) The initial portion of the formal system acceptance process within Department of Defense (DoD) acquisition procedures.

Discipline Subject matter expertise concerning or associated with a single well-defined aspect of systems engineering or other topic.

Distributed A form of organization, e.g., network structure, often associated with a set of autonomies, and the opposite of centralized.

Documentation The formal record of a system acquisition or other topic.

Note: This record may be printed, electronic, or a hybrid.

Effectiveness The quality of experiencing an acceptable degree of intended success.

Efficiency How well something is accomplished with a given expenditure of resources. This can be measured; e.g., with a TSE return on investment (ROI) analysis in terms of cost, schedule, and performance on a given program.

Elaboration An expanded or amplified explanation of a particular description.

Emergence Something unexpected in the collective behavior of an entity within its environment, not attributable to any subset of its parts, that is present (and observed) in a given view and not present (or observed) in any other view. See complex systems engineering.

Notes: Some people use a broader definition of emergence whereby whatever emerges can be expected or unexpected. For our purposes here whatever is expected is considered to be intentional, designed-in, known in advance, or at least not very surprising, and therefore does not warrant being recognized as "emergent." The most interesting aspects of emergence may well be the surprises that cannot be fully explained even after they are observed! It is suggested that complex systems engineering mostly focus on that kind of emergence; i.e., the unexplained surprises. (See "The Black Swan" by Taleb.) This distinction is made primarily to emphasize the need for a very adaptable and robust management process in the systems engineering of complex systems. It is understood that this type of collective behavior is in response to an entity's environment as well as the internal relationships among its parts.

Emergence can have benefits, consequences, or other (e.g., unimportant or [as yet] undetermined) effects. For a system, emergence can be the appearance of system behavior (state trajectories, values of adaptive parameters, or configurations in a self-organizing system) over time or across different observational views that is not predictable using existing models of the system. The perception of emergent behavior may be caused by inadequate information on the part of the observer, whether this be ignorance of intrinsic behavior at certain views, insufficient observations (or time), or insufficiently accurate knowledge of system states. True emergent behavior is a property of the system, however, not the observer, and it is uncontrollable (in the control systems sense).

Emulation Mimicking the behavior of a specific real entity for effect and efficiency.

Engineering Methodically conceiving and implementing viable solutions to existing problems.

Note: This definition does not imply that the problems are always solved.

Enterprise A complex system in a shared human endeavor that can exhibit relatively stable equilibriums or behaviors (homeostasis) among many interdependent component systems.

Features: An enterprise may be embedded in or overlap with a more inclusive complex system. External dependencies affecting an enterprise may impose environmental, political, legal, operational, economic, legacy, technical, and other constraints.

Notes: An enterprise usually includes an agreed-to or defined scope/mission or set of goals or objectives. Note also that this definition is meant to be limited. Not included here is a recipe for a successful enterprise. This is a different topic, and the purview of enterprise engineering or enterprise systems engineering.

Enterprise Engineering Application of engineering efforts to an enterprise which emphasizes enhancing the capabilities of the whole while attempting to better understand the relationships and interactive effects among its components and with its environment. See enterprise systems engineering.

Note: This definition does not necessarily imply that the "best" efforts are always applied.

Enterprise Systems Engineering (ESE) A regimen for engineering "successful" enterprises. For more information, see the papers

• A Framework for Enterprise Systems Engineering Processes
• Engineering Enterprise Systems: Challenges and Prospects
• Practicing Enterprise Systems Engineering
• On the Pursuit of Enterprise Systems Engineering Ideas.

Features: ESE is systems engineering that emphasizes a body of knowledge, tenets, principles, and precepts concerning the analysis, design, implementation, operation, performance, etc., of an enterprise. Rather than focusing on parts of the enterprise, the enterprise systems engineer concentrates on the enterprise as a whole and how its design, as applied, interacts with its environment. Thus ESE avoids some potentially detrimental aspects of TSE, such as concentrating on parts of the system and their behavior in isolation. In contrast, an ESE approach focuses on how these parts interact within the system and with its outside environment.

Notes: Here "regimen" means a prescribed course of engineering for the promotion of enterprise success. Although most people would not bother to engineer anything without attempting to make a success of the effort, some techniques applied to enterprises, such as reductionism, can be unsuccessful. See work breakdown structure.

Environment What embeds and surrounds any system.

Equilibrium A definable and notable system state that can be either stable or unstable

Note: Typically, if somehow an unstable equilibrium is slightly perturbed, that equilibrium state will migrate to another (usually stable) equilibrium state.

Ergonomics Biological relationships between a worker and the workplace environment.

Note: Concern for ergonomics has arisen in enterprises because of increasing rates of repetitive stress injuries such as carpal tunnel syndrome and lower back pain, which can impact a human-operated system's efficiency. Ergonomics is often visible in the redesign of traditional workplace furnishings and appointments. For more information, visit the International Ergonomics Association Web site.

Evolution A process of change that can be essentially unpredictable and not totally under one's control especially in those cases where human actions are involved. See complex adaptive system.

Experimentation A method of exploring hypotheses, often to inform future decisions.

F

Fielding A culminating phase of the system acquisition process.

Note: The penultimate and final phases are system sustainment and retirement.

Fitness The orthogonal combination of complexity and order. See implementation.

Notes: In the vernacular, human fitness is the condition of being physically and mentally healthy, the quality of being suitable to fulfill a particular role or task. More generally, in biology, the concept of fitness conveys the ability to survive and reproduce in a particular environment. Both aspects of fitness-order (what currently is) and complexity (what could be)-are elements of how one perceives an entity.

Form A model or pattern on which to base the execution of an object or idea. See Implementation.

Frame of Reference A perspective from which one views anything.

Note: Akin to point of view.

Framework A guiding context or generalized template conducive to performing useful work.

Function; functionality What a system does. See implementation.

G

Global Universal, all encompassing, or complete in a geographical sense; used as the opposite of local.

Global Information Grid (GIG) The Department of Defense's (DoD's) version of the Internet; i.e., a militarized Internet that exists and continues to evolve. The GIG follows a layered architecture constructed such that the communications and networking infrastructure is at the bottom of the "stack." Above that is an information management layer, followed by an application layer and, finally, at the top, the people and equipment associated with the weapon systems. The GIG also includes other foundation underpinnings such as doctrine, policies, instructions, architectures, standards, and training. For more information, see the Global Information Grid.

Goal A target that can be a desired end state or interim point consistent with the purpose at hand.

Granularity The ability of a person to discern and discriminate individual items of a conceptualization. See view.
Notes: Granularity is akin to a capability to observe details, e.g., it's like resolution. Subsets of detailed items will likely include arrangements or patterns, some of which may not be discernable in other views.

H

Health The well being of people, processes or technology.

Hierarchy A tree-like vertical structure which sometimes implies a ranking. Hierarchies are often used to depict such things as the connectivity of management entities in organizations, or the work breakdown of an acquisition program's system development phase.

Holism The concentrated practice of viewing, contemplating, analyzing, and synthesizing things as whole, to include the study of interrelationships of the parts making up the whole, and the interaction of the whole with its environment.

Feature: Central to holism is the premise or tenet that the whole is more than just a sum of its parts.

Horizontal A term used to depict the dimension, orientation, and typical span of concern when considering the overall mission capabilities provided by several/many programs. See integration and vertical.

Note: For example, horizontal integration typically applies to a collection of programs and considers what may be out of scope in terms of legal or administrative funding or direction for any given program.

I

Implementation The form and fit that realizes the functionality of a system development.

Industry A partnering group in system acquisition that specifically includes contractors responsible for producing and maintaining fielded systems. This industry does not include government, academia, non-profits; e.g., Federally Funded Research and Development Centers (FFRDC) and other service organizations.

Information Communication(s) based on processed or organized data that can convey meaning to human consumers; the raw material of knowledge.

Innovate; innovation 1. A creative process, often focused on a confluence of disparate technologies or disciplines, that leads to remarkable achievements or progress in system development that can result in system effectiveness or efficiency; 2. An invention based on often pre-existing technology, goods, services or methodologies that can improve their performance, though not necessarily their quality or acceptance.

Inputs and Outputs Data that is entered into, is processed by, and then leaves a system (usually a computer).

Note: The quality and choice of input data can affect the quality and validity of the output. This is referred to in the vernacular as "garbage in/garbage out" (GIGO).

Integration System integration is the process of organizing, uniting and regulating interactive or interdependent resources and procedures to accomplish a set of specific functions. For more information, see the DoD Enterprise Integration Toolkit.

Note: Integration can be vertical (integration within a system), horizontal (the combination of separate systems), or of capabilities, functions, etc., configured in such a way that these individual elements can operate singly or in concert without adversely affecting other elements (integration among systems).

Interoperability The ability of separate elements to provide or accept services to or from each other and to use these services to achieve mutual mission effectiveness. For more information, see the paper, Principles of Interoperability and Integration, Volume 1: Fundamentals.

Intervention Any act aimed towards engineering the environment of a complex system or set of complex systems-or of engineering the complex systems themselves.

Note: The word intervention is appropriate because one cannot presume to be in control of any complex system. Further, the intervention may or may not have a noticeable effect, or the effect may emerge with some delay. If there is a noticeable effect it can be undesirable as well as desirable. See complex systems engineering.

Iteration A single step in an evolving process that tends to be repeated, perhaps in a slightly different form, or a name for the whole process of such repetitions.

J

Jointness A condition reflecting the intentional and actual or realized integration of capabilities across the Department of Defense (DoD). For more information, see the Joint Chiefs of Staff Web site.

K

Kinematics How motion; i.e., speed, direction, distance, is described using words, diagrams, graphs, or equations.

Knowledge Data and facts after they have been learned and internalized. These have the potential to provide the insights necessary to formulate sound, appropriate decisions. (Knowledge might be described as a fluid mix of contextual information that has been integrated and interpreted to formulate factually accurate assessments, beliefs, values, perspectives and concepts, judgments, expectations, methodologies and know-how.); the raw material of understanding. See information.

L

Layered A concept of architecture where each architectural module lies logically above (or below) another, and where the only interactions allowed are between adjacent modules. See modular.

Legacy A label for existing or extant systems, usually applied to those that are already fielded and relatively (but not necessarily) mature. Even some systems still in development can fit into this category.

Life Cycle In traditional systems engineering (TSE), the sequential S-curve phases of an electronic system, from "lust to dust." This includes the statement of the client's problem, a conception or formulation of a solution, acquisition, sustainment and, finally, retirement of the system. In complex systems engineering (CSE), the S-curves overlap. Life cycles have phases. The phases of the life cycles used in TSE can be simply progressive, iterative, or some combination of both. However, they are always segmented with carefully enforced criteria for moving from one phase to the next. In CSE the phases of life cycles overlap as emergence occurs, and follow the S-curve trajectory exhibiting two important regions or "knees." These knees are generally identified as "tipping points" or phase transitions, where the overall nature or characterization of the complex system changes significantly as, by analogy, the gaseous, liquid, and solid phase or characterizations of steam, water, and ice, respectively. An examination of life cycles as understood for complex systems leads to a distinction between maturation and evolution in a system's development. The emphasis in CSE is on the evolutionary aspects of that development. For more information, see the DoD Life Cycle Management Framework Chart and the FAA Life Cycle.

Linearity A condition where the principles of proportionality and superposition apply. Reductionism and Constructionism can be applied to a linear system successfully; i.e., without it losing any functionality.

Local Restricted or limited; parochial; nearby in a geographical sense; used as the opposite of global.

Logic A systematic method of deductive reasoning which yields an opinion or conclusion. Logic is assumed to be based on information that is commonly considered contextually appropriate.

Note: Deductive reasoning can be flawed. Also, what is logical within one system might not be logical in another. Cultural variations can account for this, as can flawed reasoning.

M

Maintainability A TSE term that focuses on being able to keep a system functioning as intended. Sometimes this attribute is related to reliability and quantified as the Mean Time to Repair (MTTR), for example.

Maintenance The measures taken to safeguard, preserve and protect the attributes of a system, the goal of which is to keep it functioning as intended.

Management A process for efficiently adjudicating available resources over a specific time period to accomplish stated objectives.

Manufacturing The fabrication or assembling of a product, usually in large quantities.

Marketing The process of accessing and making known the viability and positioning of an organization's goods and services so that current and potential clients (customers and sponsors) become more interested in purchasing or otherwise taking advantage of them.

Note: Among other things, some staff should consider themselves "marketers" of an organization's systems engineering services.

Maturation The process by which an entity evolves to full development.

Measurement The act of documenting different parameters or dimensions of an entity, usually using recognized systematized standards. For example, basic units of measurement (such as weight, volume, width, etc.) are in everyday use within societies to determine an item's value. Measurement systems have become increasingly detailed and refined for use in the hard sciences, where precision is essential. For more information, see the INCOSE Measurement Tools Survey.

Measures of Effectiveness (MOE) Evaluations (usually quantitative but sometimes qualitative) of what a system should or does accomplish in support of capabilities, especially in response to its intended mission. See validation.

Measures of Performance (MOP) Evaluations (that should always be quantitative) of what a system can or does accomplish, especially in response to requirements. See verification.

Note: A MOP allows one to allocate a measure that, presumably, is traceable to a MOE but is at a lower level and more easily measured. The distinction between MOPs and MOEs is like the distinction between verification and validation: MOPs and verification test "Did you build the thing right?," while MOEs and validation test "did you build the right thing?"

Megasystem; mega-system A large, man-made, richly interconnected and increasingly interdependent system of systems (SoS). See complex system.

Note: According to this definition, a megasystem is not necessarily a complex system.

Method A set of procedures used to accomplish a task.

Note: These procedures can vary in rigor.

Metrics A quantified measurement of organizational behavior updated regularly to inform decision-making with the goal of improving performance.

Note: Metrics, i.e., the Metric System, is most often recognized as the method of standardized measurement most prevalent worldwide and generally used in the sciences.

Milestones Demarcations of the process timeline which usually highlight major events. For more information, see the DoD Life Cycle Framework View.

Note: Historically, these referred to stones used on Roman roads marking the distance from the heart of the Empire. Similar units of measurement are used on modern highways. In ESE milestones often are referred to with regard to the acquisition process.

Mindset What currently captures an individual's attention in a conceptualization. See view.

Note: Mindset is akin to one's cognitive focus that may observe or contemplate, e.g., within his scope and with the associated granularity, a single object, pattern, notion, or idea, or collection of such elements.

Modeling The process of effectively and efficiently constructing the representation of a system from a particular perspective or point of view to learn more about how it operates or might operate. See simulation.

Modular A concept of architecture where system components are aggregated and partitioned into convenient containing units (called modules). See layered.

Multi-Scale; multi-view Usually refers to dealing with more than one view of a system, enterprise, or complex system. See analysis and view.

N

Net-Centricity A collection of attributes that emphasizes the importance of a network in achieving desirable global behavior of a system or enterprise: For more information, see the paper, Net-Centric Conversations: The Unit of Work for Network Centric Warfare.

Network 1. An instance of a dynamic configuration of processing nodes and interconnecting communication links that provide the opportunity for interchange of data and information among machines or human users. 2. A collection of interconnected individuals sharing a common purpose or interest.

O

Objective 1. A quality reflected in data, information, or knowledge that has been gathered or accumulated according to a scientific method. 2. A goal.

Open Free, unobstructed by artificial means, and with unlimited participation by autonomous agents and interactions with the system's environment. See closed and complex system. For more information, see the DoD Open Systems Joint Task Force site.

Operational 1. Functional; in working order. 2. Pertaining to viable or workable/working processes and procedures.

Operational Test and Evaluation (OT&E) The final portion of the formal system acceptance process for acquisition within Department of Defense (DoD).

Operations 1. Active processes or procedures in an organization or enterprise intended to produce useful results. 2. The active technical or personal internal or interfacing relationships within or among entities which are intended to ensure a functional system.

Opportunity An uncertainty deemed to be of potentially positive benefit to a system or enterprise. See risk. For more information, see the paper, Enterprise Opportunity and Risk.

Optimum A term describing an ideal condition fostering the best performance that is or can be met by some aspect of the system, subsystem, or component. This is usually from a local (as opposed to a global) perspective, and does not consider the competing and cooperating demands of other related entities. See balance.

Note: Arguably, optimality is more feasible in TSE because the environment is less complex.

Order A qualitative measure of the nature and extent of all specific internal relationships of an entity at a moment in time.

Notes: Order characterizes the number and magnitude of concurrently existing relationships within an entity. If something has only a few relationships, it has a small order. As such relationships and the ways in which they can be expressed to grow, the level of order increases. Dynamic in form and function, order is almost always associated with organization and whatever can lead to organization. Relationships can be thought of here as patterns of attributes among the parts of the entity, and are defined by values. A relationship allows for inferring or arriving at conclusions about the specific values of an attribute of a part of an entity based on other attribute values, because these values collectively form patterns.

Organization An orderly relationship among disparate parts of a whole. See complex system and order.

Note: Organization usually is aspired to methodically by managers of people. But complex systems self-organize.

Outcome Usually the result of explicit action(s) aimed at achieving desired effects. See outcome space.

Note: Positive outcomes are those that are judged to fall within a desired outcome space.

Outcome Space The characterization of a class of possible results that might be achieved through concerted intentional action(s). See outcome.

P

Partitioning The act of separating, dividing, or dismantling an entity into distinct parts.

Perspective 1. The visual appearance of objects in relation to each other as seen from a certain distance and angle. 2. Point of view, taken figuratively one's opinion of thoughts and ideas.

Phase 1. A time period in a cycle of events. 2. A temporal affinity of similar states of a complex system. See life cycle.

Physical Descriptive property of something that exists and consists of material, substantial matter or form.

Pipelining An architectural device used in building computer systems which streamlines information processing by computing in separate stages in sequential but simultaneous fashion.

Planning A vital, continual, prospective management activity that helps better prepare for successes in traditional systems engineering, and for uncertainties and emergent behavior in enterprise systems engineering and complex systems engineering.

Populations Groups of individuals or entities of the same species or type.

Practice 1. To perform in an activity or profession. 2. The repetition of an activity with the goal of perfecting one's skill doing it.

Precept A general rule intended to regulate behavior or thought.

Precision An indication of the degree of refinement or gradation in a representation of a value or measurement. See accuracy.

Principle A fundamental truth, proposition or code that serves as the foundation for a system of belief or behavior, or for a chain of reasoning.

Problem A difficulty, predicament, dilemma or conundrum that usually must be solved to reach a goal.

Procedure An acknowledged or intentional way of doing things to achieve a desired goal. See process.

Note: A procedure could be considered a template for behavior, or a specific instantiation or tailoring of a more general process.

Process A relatively generic (compared to a procedure, at least) description of how one does things to accomplish a desired outcome or set of goals.

Product The fruit of one's personal, team, or organization's effort, or that of a system. See manufacturing and service.

Program Usually an organized and funded endeavor to create a system or accomplish a system upgrade, improvement, or consolidation over a specified or estimated time period.

Program Management A collection of oversight functions and activities intended to assure the success of the acquisition process. See systems engineering.

Notes: In traditional systems engineering this is not considered a task of systems engineering. A program's systems engineer frequently is not independent, but works for the program manager. Collective wisdom espoused particularly by systems engineers suggests that programs can be more successful if the system engineering function is independent, with both the program manager and systems engineer reporting to a higher authority. In enterprise systems engineering--especially in complex systems engineering--program management can be thought of as a sub-function of systems engineering under a broader interpretation of the latter term.

Program Manager The person in charge of a program who is responsible and accountable for meeting costs, schedules, and performance.

Project An organized and funded activity, usually in support of a sponsored program.

Note: Some organizations use the term "project" to define what its staff does in programs for their clients or customers.

Project Threats Anything that threatens the successful accomplishment of a project, be it lack of organization, needed personnel, technical expertise, clients/customers/sponsors, or funding..

Prototyping A disciplined method for trying out or proofing, in a relatively cost-effective manner, the essential elements of a potential engineering development. This enables pursuing a promising opportunity while reducing potential risks.

Proof 1. In mathematics, a reasoned, logical argument, accepted by many others, that asserts that a hypothesis is true. 2. In systems acquisition, the successful testing of a potential engineering development, arising from an original postulated concept, before incorporating it into a project or program. [Editorial thanks to MITRE's Doug Norman for this second definition, arising from his creative notion or idea.]

Q

Quality An attribute akin to system excellence when compared to an absolute standard or when measuring performance. This is determined by what users value, and is independent of available resources, schedule, or cost.

Notes: This term is "loaded." Quality is often treated as if it were a commodity to be provided by a separate person or organization to the person in charge of the system, in parallel with other persons, organizations, or sub-organizations that deliver the conception, development, fielding, sustainment, and retirement of a system. Ideally, quality should be built into everything done in connection with a system.

Quantification The act of calculating to convey the number, degree, or amount of something.

R

Reductionism The practice of simplifying a system into its constituent parts by subdividing it. One or more of these parts can then be modified or adjusted to see if it is possible to attain desired change(s) in system's functionality. See constructionism.

Note: In the social sciences this term usually carries the negative connotation of oversimplifying something complex.

Regimen A process, routine or course of action that is suggested or recommended to achieve a goal. See enterprise systems engineering and complex systems engineering; procedure and process.

Note: A regimen is more generic than a procedure or prescription. For example, a regimen suggesting a good diet and regular exercise is not as prescriptive as a specific list of food and drink for a given meal, or the numbers associated with certain workout repetitions.

Regime The domain of current interest within which something (perhaps a regimen) is applied.

Note: A regime is not to be confused with a regimen.

Relationships Connections, affiliations or correlations between or among two or more entities; e.g., people, organizations, or systems.

Note: Such liaisons are often produced because they are of mutual benefit to the members.

Reliability The quality of performing dependably, consistently, and predictably. A system's reliability is often a function of how well it has been maintained. See maintainability.

Requirements Features users often say they want and need in their operations. See capabilities. For more information, see the INCOSE Requirements Management Tools Survey.

Notes: Currently the term requirements is less appropriate in complex systems than references to capabilities, which tend to be less specific and do not change as frequently. The term is more comparable to outcomes than outcome spaces.

Resource A reserve or supply of useful or necessary items or information such as funds, personnel, expertise or equipment.

Recursion The repetition or nesting of steps, each based on the one immediately preceding it, to arrive at an outcome.

Remedial A descriptor of something that corrects, counteracts, or repairs an object, procedure, or skill.

Review A rigorous check on lessons learned (not just experienced), the current status, and plans regarding a program or project.

Note: In the case of a system of systems or enterprise, this involves a reexamination of where one has been and where one might or should go, based upon what is happening in the SoS or enterprise and its environment.

Risk An uncertainty deemed to be of potentially negative consequence in a system or enterprise. See opportunity and uncertainty.

Robustness The degree to which an entity, e.g., system, is resilient and can successfully withstand or adapt when presented with externally applied stresses or anomalies.

Role A function performed by a person or other kind of agent within a system based on capabilities or skill.

S

S Curve The classical qualitative behavior profile for many natural phenomena. Initially, a system starts evolving rather slowly. The evolution rapidly accelerates as things "jell" or catch on. As the system is accepted and increasingly utilized, its complexity increases until it gradually matures and tapers off developing with an effect of diminishing returns. The S curve is characteristic of a single system (or each of several sequential life cycle phases of a single system) but with only a single view.

Scale See view.

Schedule A plan that involves a timeframe for all of its components. Note: In Traditional System Engineering system acquisition development, it is often important that a schedule be adhered to rigorously. A more complex systems environment is likely to be a collection of interdependent schedules. A missed deadline on one schedule can adversely affect an entire plan or project. Schedules are more or less rigid, and often depend on a system's resources.

Science The human quest to understand nature and the universe.

Scope What is included in an individual's conceptualization. See view.

Notes: Conceptualization is akin to perception (e.g., visualization). Specific analogies of scope are the field of view (FoV) of a camera, or more appropriately here, the "mind's eye." When one sets or determines scope, by definition, this means that everything else, not in scope, is "abstracted out," e.g., not "seen" by that individual, at least in that View, because those things are not relevant to the person's intended present state of being, e.g., purpose.

Selection In enterprise systems engineering, selection is the act of restricting or limiting choices in the environment to shape a solution set. See variation and complexity.

Note: Too much selection can lead to stagnation which is, in most cases, not desirable.

Security That which is intended to protect a system from threats of attacks and inadvertent user actions; such things should be considered as a fundamental component system design and something essential to the system's lifespan.

Service An intangible but frequently invaluable necessary product produced by an individual, team, organization, or system.

Notes: Services are the functional counterpart of tangible "goods." While the concept of "service" is intangible, services themselves often produce measurable consequences, e.g., on an automobile, an oil change to mitigate the threat of engine freeze-up, or air added to the tires to stave off flats.

Simulation An attempt to mimic the features and character of a system to learn about real situations. See modeling.

Features: Usually simulation is more affordable and less risky than operating directly in the subject environment.

Skill A competency that is an innate, largely intangible gift, or that is acquired through learning. Skills can be applied creatively or by rote, and can lead to purposeful activities.

Note: Skills are not necessarily congruent with natural abilities or the capacity to learn. As with abilities a wide range of individual differences in skill levels prevails in all human endeavors.

Socioeconomics The social and economic impacts of an endeavor on a system and its agents.

Sociology The science of human societies.

Solution An answer to a problem.

Note: There often can be more than one solution to the same problem.

Specification In traditional systems engineering, a description of a system or sub-system that serves as a reference, for developing ideas, creating a tangible representation, or manufacturing products.

Note: Specifications are not necessarily as useful in the context of system of systems, enterprises, or complex systems because these types of systems tend to change or evolve faster and more independently than can be controlled or predicted.

Standard A method, procedure, function, or implementation that is often aspired to, identified, advocated or mandated for the overall benefit of a system and its participants because it enables or enhances efficiency or widespread interoperability.

Note: In contrast to traditional systems engineering, in system of systems, enterprise systems sngineering, or complex systems engineering contexts, standards tend to emerge more through migration of practices than by being intentionally created or pre-specified.

Stagnation; Stasis A condition of atrophy where future change is unlikely or even impossible. See chaos.

Survivability The degree to which a system can sustain itself from a natural disaster or human-made attack.

Sustainment The portion of the life cycle of an electronic system that begins with fielding the product of the acquisition phase, and ends with the system's retirement.

Synergy The enhanced positive effect resulting from, for example, the interaction of two or more people, teams, organizations, or parts of a system.

Synthesis A creation of something new with an objective in mind. See analysis.
Features: Synthesis can involve the integration of elements or ideas from two or more sources conceived from more than view.

System An interacting mix of elements forming an intended whole that is greater than the sum of its parts.

Features: These elements may include people, cultures, organizations, policies, services, techniques, technologies, information/data, facilities, products, procedures, processes, and other human-made or natural) entities. The whole is sufficiently cohesive to have an identity distinct from its environment.

Note: In general, a system does not necessarily have to be fully understood, have a defined goal or objective, or have to be designed or orchestrated to perform an activity. However, in the present definition, "intended" means an understood/defined goal/objective and designed/orchestrated to perform a useful activity.

Systems Engineer A person knowledgeable in various disciplines and able to, either directly or indirectly, conceive, research, utilize, design, develop, fabricate, produce, integrate, test, deploy, operate, sustain, and retire one or more system elements.

Features: Among other things, the systems engineer oversees the definition and refinement of a system's requirements, architecture, and integrity.

Systems Engineering An iterative and interdisciplinary management and development process that defines and transforms requirements or desired capabilities into an operational system. For more information, see the INCOSE Web site.

Features: Typically, this process involves environmental, economic, political, and social aspects. Activities include conceiving, researching, architecting, utilizing, designing, developing, fabricating, producing, integrating, testing, deploying, operating, sustaining, and retiring system elements.

Notes: The customer for or user of the system usually states the initial version of the requirements. The systems engineering process is used to help better define and refine these requirements. Further, the requirements often change as new decisions are made as a result of systems engineering. This definition does not imply that a successful system is always realized. The word "integrated" is not included in this definition because systems engineering efforts are not always that well integrated.

System of Systems (SoS) A collection of systems that functions to achieve a purpose not generally achievable by the individual systems acting independently. For more information, see the paper, Systems of Systems Engineering in the Enterprise Context: A Unifying Framework for Dynamics.

Features: Each system can operate independently and is managed primarily to accomplish its own separate purpose. An SoS can be geographically distributed, and can exhibit evolutionary development or emergent behavior.

T

Task An organized and funded sub-activity, usually in support of a project.

Technology The non-human material means for accomplishing capabilities

Notes: Technology usually comes in a combinative form of software and hardware. Technical means are broader than technology in that they may be non-material, such as ideas, algorithms, procedures, etc.

Tenet A principle or belief, especially one of the main ideas of a religion or philosophy.

Note: A tenet is intended to be an accepted or self-evident principle. Adoption of a tenet can be similar to adopting a religious belief.

Testing Technical assessments done at key checkpoints to find out how well a system works. See milestones and proof.

Threat Anything that menaces or puts a system at risk.

Note: Threats have predominantly negative implications.

Timeframe The time interval of an individual's conceptualization. See view.

Note: Timeframe is akin to temporal component of one's conceptualization; e.g., the timescale over which it occurs.

Top-Level Design The "blueprint" which lays out the design of an entire (but relatively simple) system.

Note: More complex systems cannot be fully designed by top-level methods alone.

Traceability The extent to which information about every step, process, or phase in a series of these can be discovered or recovered.

Traditional Systems Engineering (TSE) Systems engineering where limited attention is paid to the non-technical or complex system aspects of the system.

Features: In TSE there is emphasis on the process of selecting and synthesizing the application of appropriate scientific and technical knowledge in order to translate system requirements into a system design. In this case it is normally assumed and assured that the behavior of the system is completely predictable. Traditional engineering (not just TSE) typically is directed at the removal of unwanted possibilities and avoiding any surprises.
Note: It is also assumed that TSE is identical to "classical" systems engineering, i.e., customary and accepted methods of doing system engineering.

Transdisciplinary Refers to the potential innovation and synergy arising from distinctly different branches of engineering, scientific, cultural, etc., knowledge.

Note: The term transdisciplinary is more a propos enterprise systems engineering and complex systems engineering. The word "multidisciplinary" is usually used in traditional systems engineering.

Transformation A fundamental reconfiguration, morphing, or phase change of an entity which alters its observable characteristics significantly.

U

Uncertainty A state of doubt, ambiguity, or lack of knowledge which can result in a lower confidence level regarding proper potential future courses of action. See opportunity and risk.

Understanding Deep awareness of the critical factors, patterns, and logic of a situation resulting from the synthesis and application of knowledge, judgment and intuition; the raw material of wisdom.

Note: Understanding allows one to anticipate the consequences of one's actions;

Usability The extent to which any product meets the goals of its user, and can be easily understood and employed for the purpose for which it was designed.

Note: In the context of information technology systems, usability implies qualities such as intuitive design features, simplicity, reliability, and user-friendliness.

V

Validation The act of determining and asserting that something is correct. See measures of effectiveness.

Variation In the context of enterprise systems engineering, the act of allowing or encouraging perturbations in the environment with the intention of creating a richer variety of potentially attractive solutions. See selection and complexity.

Note: Too much variation can lead to chaos, usually an undesirable state of affairs.

Verification The act of confirming that something is true, or at least represents what was intended. See proof and measures of performance.

Vertical A term used to depict the dimension, orientation, and typical span of concern in a traditional ("stovepipe") systems engineering program. See horizontal and integration.

Note: Single programs tend to be integrated vertically, given their funding, legal mandates, and they way in which they are administered and managed.

View Any combination of scope, granularity, mindset, and timeframe.

Features: A change in any one of these elements will result in a change of view; i.e., what one can perceive or understand.

Notes: The limitations of the human brain make it practically impossible for a person to essentially grasp the underlying "reality" of any situation. Rather, each person viewing something focuses his or her mind on a mental snapshot or perspective of a situation. One understands it only to a certain extent (or scope) with its associated level of granularity (detail), abstracting out what appears to be irrelevant for one's own particular viewpoint. Even someone totally unfamiliar with enterprise systems engineering can identify with the saying, "If you can't change the situation, change your attitude." Attempting to take a fresh look at something familiar from unfamiliar points of view can be a useful device to gain further understanding of a system.

W

Waterfall In traditional systems engineering, a metaphor typically used to describe the software development process. See constructionism and reductionism.

Note: Although many feedback loops are embedded in the original depiction of the waterfall model, this process becomes somewhat corrupted in practice. It is often denigrated because it has been shown that the serial characterization of the steps does not work well.

Wisdom The most prized level or scale of human processing (superior to data, information, knowledge and understanding). Wisdom can guide an individual's actions in an appropriate manner-if that person acquires it.

Work Breakdown Structure A divide-and-conquer procedure to manage work effectively.

Notes: This procedure is quite entrenched in the traditional systems engineering process and is consistent with reductionism/constructionism. However, work breakdown structures usually are not as effective in system of systems engineering, enterprise systems engineering, or complex systems engineering because these systems tend to change continually, in spite of conventional engineering efforts.

X

X- A (sometimes sub-) prefix used to denote the extreme version of an entity, activity, language, pastime, or sport; e.g., an experimental version of military hardware weapons systems (e.g., X-planes), eXtensible Markup Language (XML).

Y

Z

Z The last letter in the lettering system known as the Latin alphabet.

Zachman For more information, see the Zachman Institute for Framework Advancement.

Glossary