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Systems Modeling & Simulation Working Group

The following was compiled by members of the Systems Modeling & Simulation Working Group to provide the model-based systems engineering community with a common set of shared terms and definitions.

A-C | D-F | G-I | J-L | M-O | P-R | S-U | V-X | Y-Z

Terms & Definitions (D-F)

Term Definition Source
Data A representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing by humans or by automatic means. (DoDD 8320.02) Modeling & Simulation Coordination Office
Data Asset Any entity that is comprised of data. For example, a database is a data asset that is comprised of data records. A data asset may be a system or application output file, database, document, or web page. A data asset also includes a service that may be provided to access data from an application. For example, a service that returns individual records from a database would be a data asset. Similarly, a web site that returns data in response to specific queries (e.g., would be a data asset. A human, system, or application may create a data asset. (DoDD 8320.02) Modeling & Simulation Coordination Office
Data Certification The determination that data have been verified and validated. Data user certification is the determination by the application sponsor or designated agent that data have been verified and validated as appropriate for the specific M&S usage. Data producer certification is the determination by the data producer that data have been verified and validated against documented standards or criteria. (IEEE Std 1278.3-1996) Modeling & Simulation Coordination Office
Data Dictionary A specialized type of database containing metadata that is managed by a data dictionary system. A repository of information describing the characteristics of data used to design, monitor, document, protect, and control data in information systems and databases. Modeling & Simulation Coordination Office
Data Logger A device that accepts data outputs from a simulation or federation and stores them for processing and replay. Modeling & Simulation Coordination Office
Data Model In a database, the user's logical view of the data in contrast to the physically stored data, or storage structure. A description of the organization of data in a manner that reflects the information structure of an enterprise. (SISO-REF-002-1999) Modeling & Simulation Coordination Office
Data Verification And Validation The process of verifying the internal consistency and correctness of data and validating that it represents real-world entities appropriate for its intended purpose or an expected range of purposes. (DoDI 5000.61) Modeling & Simulation Coordination Office
Decision gate A decision gate is an approval event (often associated with a review meeting). Entry and exit criteria are established for each decision gate; continuation beyond the decision gate is contingent on the agreement of decision-makers.

Democratization of Simulation

Expanding significantly the user community of Engineering Simulation capabilities that result in benefits of reduced time and cost, and more reliable product lifecycle studies.


Dependent Variable A variable whose value is a function of one or more independent variables. Contrast with: independent variable (SISO-REF-002-1999) Modeling & Simulation Coordination Office
Derived Requirements Detailed characteristics of the system-of interest that typically are identified during elicitation of stakeholder requirements, requirements analysis, trade studies or validation
Descriptive Model A model used to depict the behavior or properties of an existing system or type of system. (SISO-REF-020-2007) Modeling & Simulation Coordination Office
Design Constraints The boundary conditions, externally or internally imposed, for the system-of-interest within which the organization must remain when executing the processes during the concept and development stage
Deterministic Model A model in which the results are determined through known relationships among the states and events and in which a given input will always produce the same output; for example, a model depicting a known chemical reaction. Contrast with: Stochastic Model. (SISO-REF-020-2007) Modeling & Simulation Coordination Office
Digital Twin

A digital surrogate that is a description of a physical asset such as one or more products, processes, systems, people and devices that can be used for various purposes. It makes use of data to/from its real-world asset and may change in tandem throughout the lifecycle of the physical asset.


Discovery Metadata A type of metadata that describes or summarizes key attributes and concepts, and allows assets (e.g., a model, simulation, or data) to be found using enterprise-level search capabilities. (DoDI 5000.70) Modeling & Simulation Coordination Office
Discrete Event Simulation (DES) A simulation where the dependent variables (i.e., state indicators) change at discrete points in time referred to as events. Modeling & Simulation Coordination Office
Discrete Event Simulation Specification (DEVS) A modeling formalism, methodology and specification framework that provides a theoretical foundation independent of programming languages and hardware platforms. Modeling & Simulation Coordination Office
Discrete Model A mathematical or computational model whose output variables take on only discrete values; that is, in changing from one value to another, they do not take on the intermediate values. Contrast with: continuous model. (SISO-REF-020-2007) Modeling & Simulation Coordination Office
Distributed Simulation A simulation that has multiple modules, which can be run on multiple processors. The processors can be co-located in the same room or located in remote sites. Modeling & Simulation Coordination Office
Dynamic Analysis An analysis that includes the effect of the variables changing with time as well as space. NAFEMS
Emergent Behavior A behavior or property that appears when a number of simple entities (agents) operate in an environment, forming more complex behaviors as a collective. Modeling & Simulation Coordination Office
Emulation A model that accepts the same inputs and produces the same outputs as a given system. (SISO-REF-002-1999) Modeling & Simulation Coordination Office
Emulator A device, computer program, or system that performs emulation. (SISO-REF-002-1999) Modeling & Simulation Coordination Office
Enabling System A system that supports a system-of-interest during its life cycle stages but does not necessarily contribute directly to its function during operation. Airbus
Engineering Simulation

The use of physics-based mathematical (numerical) models and/or logical models, including relevant data derived from their physical model counterparts, as representations of a conceptual or real-world system, phenomenon, or process in studying its technical requirements and operational behavior.


Enterprise Model Information model(s) that presents an integrated top-level representation of processes, information flows, and data. Modeling & Simulation Coordination Office
Entity A distinguishable person, place, unit, thing, event, or concept about which information is kept. (SISO-REF-020-2007) Modeling & Simulation Coordination Office
Environment The surroundings (natural or man-made) in which the system-of-interest is utilized and supported; or in which the system is being developed, produced or retired. INCOSE
Event A change of object attribute value, an interaction between objects, an instantiation of a new object, or a deletion of an existing object that is associated with a particular point on the federation time axis. Each event contains a time stamp indicating when it is said to occur. Modeling & Simulation Coordination Office
Event List An ordered list that contains the time all events will occur. Modeling & Simulation Coordination Office
Event-Driven Simulation A simulation in which attention is focused on the occurrence of events and the times at which those events occur. (IEEE 610.3-1989) Modeling & Simulation Coordination Office
Executable Model A model that instantiates the conceptual model of a system as its design specification. Modeling & Simulation Coordination Office
Expert System A knowledge collection combined with an inference engine capable of interpreting queries and chaining together separate items of knowledge to develop new inferences. Modeling & Simulation Coordination Office
Facility The physical means or equipment for facilitating the performance of an action, e.g. buildings, instruments, tools
Feature An element of the synthetic environment that does not actively participate in interactions. Features are passive and do not initiate action. Modeling & Simulation Coordination Office
Federate In HLA, an application that may be or is currently coupled with other software applications under a Federation Object Model (FOM) Document Data (FDD) and a runtime infrastructure (RTI). (IEEE Std 1516.2-2010) Modeling & Simulation Coordination Office
Federated The ability to search across multiple archives, data collections, or multiple content aggregator services. (DoDI 5000.70) Modeling & Simulation Coordination Office
Federation In HLA, an application that may be or is currently coupled with other software applications under a Federation Object Model (FOM) Document Data (FDD) and a runtime infrastructure (RTI). (IEEE Std 1516.2-2010) Modeling & Simulation Coordination Office

Federation Object Model (FOM) A specification defining the information exchanged at runtime to achieve a given set of federation objectives. This information includes object classes, object class attributes, interaction classes, interaction parameters, and other relevant information. The FOM is specified to the runtime infrastructure (RTI) using one or more FOM modules. The RTI assembles a FOM using these FOM modules and one Management Object Model (MOM) and Initialization Module (MIM), which is provided automatically by the RTI or, optionally, provided to the RTI when the federation execution is created. (IEEE Std 1516.2-2010) Modeling & Simulation Coordination Office
Federation Of Models And Simulations A system of interacting models, simulations, and supporting infrastructure that are based on a common understanding of the objects portrayed in the system. (MIL-STD-3022) Modeling & Simulation Coordination Office
Fidelity The degree to which a model or simulation represents the state and behavior of a real world object or the perception of a real world object, feature, condition, or chosen standard in a measurable or perceivable manner; a measure of the realism of a model or simulation. Modeling & Simulation Coordination Office

Field Programmable Gate Array in the Loop (FPGA) ~~ (FIL)

A simulation approach that incorporates a configured FPGA running an algorithm within a virtual simulation environment to enable simultaneous development of system software (SW) with hardware (HW) resulting in system performance simulations very early during development.


Final Condition The values assumed by the variables in a system, model, or simulation at the completion of some specified duration of time; final state. (IEEE Std 610.3-1989) Modeling & Simulation Coordination Office
Finite Differences A numerical method for solving partial differential equations by expressing them in a difference form rather than an integral form. Finite difference methods are very similar to finite element methods and in some cases are identical. NAFEMS
Forced Response The dynamic motion results from a time varying forcing function. NAFEMS
Function An action, a task, or an activity performed to achieve a desired outcome. Hitchins / SEBoK
Functional Architecture Set of functions and their sub-functions that defines the transformations of input flows into output flows performed by the system to achieve its mission. SEBok
Functional Mock-up Interface (FMI) A group of companies, institutes and universities organized under the umbrella of the Modelica Association are defining Functional Mock-up Interface (FMI) as a tool independent (open) standard to support both model exchange and co-simulation of dynamic models using a combination of xml-files and compiled C-code. INCOSE
Functional Mock-up Unit (FMU) The instantiation, initialization and/or execution of an individual executable (or C code) model representation performed within a simulation environment. The FMU contains a concrete mathematical model described by differential, algebraic and discrete equations with possible events of a dynamic physical system transformed into explicit form and represented as C code or machine code. White Paper