Author: Joe H., Inflow Engineer
In our previous post The Iterative Approach to Problem Solving we talked about how effective it can be to break a problem into segments and solve it gradually. One of the best ways to split a problem into smaller parts is a technique known as "black boxing". Before we can talk about how or why we might want to use black boxing, we need to go over what a black box is in this context.
A black box, at least from an engineering perspective, is a system where you only know the inputs and outputs, not the internals. In other words, you have a black box that does something, and you can see what it outputs for various inputs, but you don’t have any clue what’s happening inside the box. A black box can be anything from an automatic transmission to a computer. You don’t need to understand every detail inside a transmission or a computer to use it in your daily life, you just need to know what inputs you need to use to get the output you want. When used properly, a black box can convert a system with millions of components into a system with just a few pieces.
This inherent simplification is what makes black boxing such a powerful tool for solving problems, as well as designing and analyzing systems. By creating black boxes around each complex part of the system, you can turn it into a set of simple components with inputs and outputs. A design for a spaceship, for example, might consist of an engine black box, a crew module black box, a flight control black box, etc. Once you have those high level systems blocked out, you determine what the inputs and outputs are. The engine black box, for example, could have two inputs, fuel and throttle, and two outputs, thrust and heat. You can do the same for each black box, and you might even decide to treat the whole spaceship as a black box that uses fuel, food, water, and astronauts as inputs, and outputs thrust and astronauts. This gives you a good high level understanding of how your overall system is set up. You know what inputs each part of your design needs to function, what outputs it provides to the other parts of the system, and how they’re all tied together. This is exactly what you need to identify if you are trying to take an iterative, incremental approach to design.
As I hope you noticed, in the last paragraph we analyzed our spaceship design as a black box composed of smaller black boxes. This nested approach is what makes black boxing such a great analysis tool, since you can start by focusing either on how the system functions as a whole and then drilling down into the details, or by focusing on a specific sub-system and building up to understand the overall picture. The spaceship design is an example of the top down approach, and if you were actually planning to complete the design, you would end up looking inside each of the high level black boxes and breaking them down even further, until you got to the point where you were designing individual elements. By iterating the black box process over and over again, you’re left with simple components and a map of how they connect functionally to make a complex system.
Black boxing is an incredibly powerful approach to designing, but as I noted earlier, it can also be used for analyzing an existing device. Using a bottom up approach to black boxing allows us to determine the function of a small part of the device under analysis, and then create a black box around those components. Even if the overall function of the device isn’t obvious, you can create black boxes around most of the components. For highly complex devices, you might have to iterate the process and create black boxes out of black boxes. After a few iterations, you’ll be left with what’s called a functional block diagram of the whole system, which is a simplified representation of a system using interconnected black boxes. As one would expect, the bottom up approach is essentially the opposite of the top down approach.
The real key to both approaches is the looking at a complex system as a set of independent, interconnected sub-systems. With the top down approach we break the system down to do this, and with the bottom up approach we build the components up into groups to achieve the same thing. When it comes to problem solving instead of system design or analysis, the same methods apply. Think of all the things the solution to your problem needs to accomplish, and make each one the output of its own black box with an appropriate set of inputs.
For example, if you want to reduce overhead costs in a factory, you could look at the total cost of labor and materials and try to adjust that across the board. However, if you use a black boxing approach, you might look at each different type of machinery as a different black box with inputs such as labor costs, materials, the outputs of other machines, and time, and with an output of whatever that machine makes. With this deeper understanding of the situation, you may be able to make more precise adjustments that will result in greater cost reductions.This method of thinking is not unique to engineering by any stretch of the imagination (the last example is a process that should be very familiar to any operations manager), although it’s normally not called out explicitly in other fields. Because of this, gaining a deeper understanding of how to black box allows non-engineers to get more out of the tasks they already perform. One of the best illustrations of this is organizational charts. An organizational chart of a company breaks the company down into discrete groups, which is a major part of black boxing. Typically, there’s no real focus on the inputs and outputs of each group, but if you understand how to use a black boxing approach, you can add them in to get a better understanding of how each business unit interacts with the others. Now, instead of just a chart of who reports to whom, you can see at a glance what output each unit produces, which units support other units, and what each group needs to continue operating. Perhaps there are places where changes to group interactions can lead to major efficiency gains, or maybe a group is producing an output that is being under-utilized.
Learning how to use the black box approach takes time, but it can be a powerful tool no matter what field you’re working in. Odds are, you’re already using the basic principles without knowing it. Take some time to really look at how you approach problems in your field, and I’m willing to bet you’ll find multiple places where consciously applying black boxing can make the whole process simpler.
-Joe H., Inflow Engineer
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