System development and methodology are often described in terms of the Life Cycle V model (Figure 1-1). Simple and straightforward, this view covers the development of most systems. In terms of methodological execution, there has been a move toward Agile Systems Engineering, generally described by Figure 1-2. Note that the phases in the circular portion of the figure are essentially the left leg of the System Engineering V model. The primary difference between them is that the Agile version shows Stakeholder Needs vs. Stakeholder Requirements. For the purposes of modeling, consider these as equivalent statements since the needs are normally stated (by the acquisition agency) as capability requirements.