Functional Analysis is about trying to capture the Behaviour that the system “Must Do” in order to achieve its mission.
There are three tools that Systems Engineers use to define functionality namely;
Sequence Diagrams and
For each use case the systems engineers will model the behaviour needed.
Functional Flow diagrams are useful in describing the “sunny day scenario” for a particular Use Case. They are very good at describing the flow of mater energy and control in a system. If however, there are a number of branches or conditions they quickly become complex and hard to follow. In these cases it might make more sense to continue building the functional model using Sequence Diagrams.
Sequence Diagrams are easily understood and can be a useful way to gain stakeholder acceptance of the functionality being captured. Sequence diagrams have the ability to describe all of the flow and control of a functional flow diagram however, it is usual to avoid this complexity and just draw additional sequence diagrams for each scenario. This approach makes the sequence diagrams easier to review and approve with stakeholders.
State Diagrams are a very flexible way to capture functionality but they can be harder to understand. Their main advantage is that when used in an MBSE tool they can be used to simulate the behaviour of the system and validate the system requirements.
Functional Analysis is really the key to a systematic understanding of your requirements.
Contact us if you would like to discuss how Functional Analysis can help you capture the requirements on your next project.