## 4 Discussion  
In this article, we have defined and described a metamodel and to associated practice of using T3 SD. We have also described an overview of DEVS. This led to a description of DEVS-based simulation framework for T3 SD and mapping between T3 SD and DEVS. Here we provide a recommendation for a path to convergence.  
The T3 SD framework is focused on the modeling of the engineering of systems. A major aspect of SE is problem formulation. The T3 SD framework defines the problem space through the set of system design requirements (SDR). We recommend using this as the starting point for problem formulation. With the exception of the IOR, we recommend  
Figure 14: Conceptual overlay of T3 SD terms (left-side) and DEVS (right-side). This figure shows the approximate equivalence between T3 SD elements and DEVS elements. There is no equivalence of the DEVS elements multi-component system and structured system to T3 SD elements.  
using the performance (PR), cost (CR), technology (TYR), and tradeoff (TR) requirements for problem formulation. The structure of these requirements allows for defining the problem space and separating the systems (models) that are acceptable from those that are not.  
The I/O frame, relation, and function of DEVS provide an incremental process that leads to establishing simulatable system models. The IOR of T3 SD is not expressly focused on simulation. Therefore, where simulation is desired, the DEVS formulation should serve as the basis over the IOR of T3 SD.  
As we showed in Figure 14, the I/O system is mapped to multiple aspects of T3 SD. In this case, all of the identified aspects of T3 SD are system models represented as single state machines. The I/O system of DEVS accounts for simulation capability that does not appear to be inherent in T3 SD. The I/O systems inherently account for a transition state from the receipt of an input to a state of production of output. This capability is not expressly defined as being a part of the simple Moore-based state machines of T3 SD. Therefore, the recommendation is to use the I/O system of DEVS in place of the functional system model (Z), functional system design (FSD), resultant system model (Z@), and system mode (ZS) of T3 SD.  
The BSD, with its system coupling aspect (SCR) of T3 SD, is approximately equal to the network of systems within DEVS. Because the ISD contains the BSD, we mapped both to the network of systems. However, as a recommended convergence between T3 SD and DEVS, the ISD should be a vector containing a network of systems representing the buildable system (BSD), I/O system representing the system mode(s) (ZS), I/O system representing the functional system (FSD and Z), and the morphic mapping between all the system models.  
Future research should be focused on defining and providing holistic demonstration of the merged methodology between T3 SD and DEVS. This is expected to require T3 SD to be implemented as a software program. From this, comparison to the many DEVS implementations and updates toward a merged software implementation is possible. Furthermore, this future research could entail and enable empirical assessment and comparison to other research efforts toward a scientific foundation for MBSE.