Published here April, 2003.

Introduction | The PMI's Guide to the PMBoK | The "Waterfall" Process
The Systems Engineering Approach | The Spiral Model Approach | PART 2

The Systems Engineering Approach

The systems engineering approach is also a linear process. Perhaps the best example is the "Vee Model" as depicted in Figure 2 and described in detail by Forsberg, Mooz and Cotterham.[8]

Figure 2: The "Vee" Model (Mooz, et al, 1996)
Figure 2: The "Vee" Model (Mooz, et al, 1996)

But as Cantor explains:[9]


Systems engineering is concerned with designing, specifying, and verifying the implementation of components of complex systems. It was developed to meet the challenge of building large aerospace systems such as the Space shuttle and NATO's command and control systems. These systems are often so large that their development must be distributed to several companies. One firm, the prime contractor, is assigned overall design and integration of the system. The prime contractor's systems engineers gather and analyze the system requirements, then design the system by decomposing it into a set of subsystems.


The subsystems may be developed by subcontractors, who are obligated by contract to meet the requirements and specifications for the subsystems. The developed subsystems are delivered to the prime contractor for integration into the total system. The prime contractor's systems engineers verify that the subsystems meet their requirements and oversee integration.


Initially, the systems engineering approach may seem to be a reasonable approach to developing large software systems. Many systems engineering activities apply to software development:

  • Requirements gathering and analysis
  • Architecture (identification and specification of the systems)
  • Subsystem development
  • Integration and verification

However, the systems engineering approach is based on assumptions that do not apply very well to software development. Systems engineering assumes the requirements are stable and the interfaces can be specified adequately before implementation. In practice, the systems approach is a particularly rigid variant of the waterfall approach and its lifecycle, and it inherits all the weaknesses of that approach:

  • Classical systems engineering is document driven. Systems engineering efforts are driven by formal documents that are developed by engineers and implemented by developers. The problem is that the documents are never correct. The systems engineers rely on their ability to make the document correct. They focus on creating specifications that, once approved, are adequate for determining the design of each subsystem. Any change to the document is managed by a cumbersome change control-board system.

End Quote

Good features

  • Most people who have an engineering background are very comfortable with the systems approach
  • It is very good wherever it is possible to describe, i.e. specify, the requirements with a high degree of certainty
  • The acquiring authority requires a thoroughly well-documented track record or audit trail
  • Consequently, it is popular with big government departments,
  • Where money is not the limiting criteria, though competitive bidding might be.

Not so good features

  • The process is heavy on documentation
  • It assumes that it is possible to arrive at near-perfect documentation that is complete, and is truly representative of the ultimate "requirements"
  • And can be frozen, and the authors, i.e. the stakeholders, can be held accountable to those requirement specifications.

In summary, this approach does not fit well with the IS department's environment, sometimes described as "the voyage of discovery", that we described in our introduction.

The "Waterfall" Process  The "Waterfall" Process

8. Kevin Forsberg, Mooz, M. and Cotterham, H. , Visualizing Project Management, 2nd Edition, Wiley, 2000
9. Murray Cantor, Software Leadership: A Guide to Successful Software Development, Addison-Wesley, NY, 2002, Appendix A.2, p162
Home | Issacons | PM Glossary | Papers & Books | Max's Musings
Guest Articles | Contact Info | Search My Site | Site Map | Top of Page