## 3 Results
### A Brief Review of DEVS and Associated Formalism
#### 3.2.1 Overview of the DEVS  
The DEVS formalism formalizes what a model is, what it must contain, and what it does not contain (for instance, experimentation and simulation control parameters are  
Figure 10: Practical illustration of the Implementability perspective to showcase the process for engineering a flashlight; including the homomorphic relationship between the functional and buildable designs that meet both the required input/output, meet the required technology availability, and are ordered according to the preferred tradeoff. The diagram does not represent a single model of the system, but a solution space. Each pair state machine/block diagram represents one possible solution inside the implementability space. This figure is used only to support our narrative to explain [PERSON]’s T3 SD. The figure is NOT a formal visualization of any model.  
not contained in the model). Moreover, DEVS is universal and unique for discrete-event system models. Any system that accepts events as inputs over time and generates events as outputs over time is equivalent to a DEVS model. With DEVS, a model of a large system can be decomposed into smaller component models with couplings between them. The DEVS formalism defines two kinds of models: (i) atomic models that represent the basic models providing specifications for the dynamics of a system components, and (ii) coupled models that describe how to couple several component models (which can be atomic or coupled models) together to form a new model. This hierarchical construction stems from the proof that a coupled model behaves like an atomic model due to DEVS formalism's closure under coupling which is strongly linked to systems being well-defined [36].  
An atomic DEVS model can be considered as an automaton with a set of states and transition functions allowing the state to change when an event occurs or due to the passage of time. When no events occur, the state of the atomic model is updated by the internal transition function upon expiration of its lifetime. When an external event occurs, the atomic model intercepts it and changes its state by applying its external transition function. The lifetime of a state is determined by a time advance function. Each state change can produce output messages via the output function. Examples of such DEVS models, including atomic and coupled models in operation, can be found in [10].  
An abstract simulator algorithm is associated with the DEVS formalism in order to execute the structure of a model to generate its behavior. This technology-free abstract simulator standard enables DEVS models to be simulated on multiple different execution platforms, including those on desktops (for development) and those on high-performance platforms (such as Clusters or High Performance Computers).  
The DEVS formalism includes continuous, parallel, coupled, networked, and Markov modeling (probabilistic) [10]. The DEVS formalism has been demonstrated for SoS application [42, 43]. Furthermore, the basis of DEVS on [PERSON]'s system definition suggests that the foundation for the pairing of DEVS with T3 SD is already present [10].  
The Iterative System Specification and its relation to the DEVS formalism enables defining various continuous, discrete, and hybrid models for which simulations are possible [10]. The concept of system coupling has been proven within DEVS to allow for coupling of both discrete and continuous systems through closure under coupling [36]. The Iterative Specification of DEVS also allows for use of morphisms to maintain measured consistency and deviation throughout the specification of the various system models [10].