Editing Systems engineering (section)

===Modeling formalisms and graphical representations===
Initially, when the primary purpose of a systems engineer is to comprehend a complex problem, graphic representations of a system are used to communicate a system's [[functional requirement|functional]] and data requirements.<ref>{{Cite web|url=http://www.vitechcorp.com/resources/technical_papers/200701031634430.CommonGraphicalRepresentations_2002.pdf|title=Relationships between Common Graphical Representations in System Engineering|last=Long|first=Jim|publisher=[[Vitech Corporation|VitechCorp]]|date=2002|archive-url=https://web.archive.org/web/20170813085941/http://www.vitechcorp.com/resources/technical_papers/200701031634430.commongraphicalrepresentations_2002.pdf|archive-date=13 August 2017}}</ref> Common graphical representations include:
* [[Functional flow block diagram]] (FFBD)
* [[Model-based design]]
* [[Data flow diagram]] (DFD)
* [[N2 chart]]
* [[IDEF0|IDEF0 diagram]]
* [[Use case|Use case diagram]]
* [[Sequence diagram]]
* [[Block diagram]]
* [[Signal-flow graph]]
* [[Universal Systems Language#Formalism for a theory of control|USL function maps and type maps]]
* [[Enterprise architecture framework]]s

A graphical representation relates the various subsystems or parts of a system through functions, data, or interfaces. Any or each of the above methods is used in an industry based on its requirements. For instance, the N2 chart may be used where interfaces between systems are important. Part of the design phase is to create [[Structural model (software)|structural]] and [[behavioral model]]s of the system.

Once the requirements are understood, it is now the responsibility of a systems engineer to refine them and to determine, along with other engineers, the best technology for a job. At this point starting with a trade study, systems engineering encourages the use of weighted choices to determine the best option. A [[decision matrix]], or Pugh method, is one way (QFD is another) to make this choice while considering all criteria that are important. The trade study in turn informs the design, which again affects graphic representations of the system (without changing the requirements). In an SE process, this stage represents the iterative step that is carried out until a feasible solution is found. A decision matrix is often populated using techniques such as statistical analysis, reliability analysis, system dynamics ([[feedback control]]), and optimization methods.