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Functional Allocation VIII

Typically, the first type of allocation work performed on a large and complex product is the shall-to-function (STF) allocation task. The figure below shows the inputs and outputs of the STF allocation process. Note that it is not enough to simply identify, enumerate, and define the product functions in isolation. An integral sub-activity of the process is to conjure up and define the internal and external functional interfaces.  Since the dynamic interactions between the entities in an operational system (human or inanimate) give the system its power, I assert that interface definition is the most important part of any allocation process.

Shalls To Functs II

The figure below illustrates two alternate STF allocation outputs produced by different people. On the left, a bland list of unconnected product functions have been identified, but the functional structure has not been defined. On the right, the abstract functional product structure, defined by which functions are required to interact with other functions, is explicitly defined.

Func Ifaces

If the detailed design of each product function will require specialized domain expertise, then releasing a raw function list on the left to the downstream process can result in all kinds of counter productive behavior between the specialists whose functions need to communicate with each other in order to contribute to the product’s operation. Each function “owner” will each try to dictate the interface details to the “others” based on the local optimization of his/her own functional piece(s) of the product. Disrespect between team members and/or groups may ensue and bad blood may be spilled.  In addition, even when the time consuming and contentious interface decision process is completed, the finished product will most likely suffer from a lack of holistic “conceptual integrity” because of the multitude of disparate interface specifications.

It is the lead system engineer’s or architect’s duty to define the function list and the interfaces that bind them together at the right level of detail that will preserve the conceptual integrity of the product. The danger is that if the system design owner goes too far, then the interfaces may end up being over-constrained and stifling to the function designers. Given a choice between leaving the interface design up to the team or doing it yourself, which approach would you choose?

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