PBP - Boundaries

In engineering, especially in firmware and electrical engineering, there is a concept of system boundaries. Most systems take some sort of input, perform some type of processing, and deliver an output.

I tend to think of my life in the same way I think of an engineering project. I tried to relate the diagrams I create everyday to my everyday life. Feel free to skip my rambling.


Let's say that our system is a television. This is an abstract example that can get complicated quickly, so I'm leaving out a lot of technical details on purpose.

When we watch TV, what can you actually do with the TV? You can hear the audio, watch the video, adjust the volume, and change the channel. This is the first system boundary. From the TV's standpoint, it takes two inputs (volume and channel) and provides two outputs (audio and video).

System Diagram 1
System Diagram 1

On the other side of the TV, it takes a third, hidden input that we can't see: the cable line.

System Diagram 2
System Diagram 2

Inside the TV, there are subsystems. The audio and video for the channel you chose is selected, so an input filter (technically, a "demultiplexerpbp-boundaries-fn1") allows only that channel's audio and video into the rest of the TV. All of the other channels are filtered out.

The audio and video have to be handled separately, so they are split apart.

The video feed is sent to a driver that displays it on the screen.

The audio feed is sent to an amplifier. This amplifier adjusts the volume of the audio feed according to the viewer's setting. Then, the amplified audio is sent to the speaker.

We see the screen and hear the speakers, completing the system.

System Diagram 3
System Diagram 3

This is going somewhere, I swear!


In a layer diagram, we take the system diagram above and stack it into a neat block. A box can only "see" what is beneath it. Inputs (if any) go downward. Outputs go upward.

So, in the diagram below, the person can only interact with the television, and the television can interact with the person and the cable line. The cable line outputs its signal to the television, and the television outputs its entertainment to the person. The television accepts input from the person (volume and channel).


So, the entire system looks something like thispbp-boundaries-fn2:

Channel Volume Speakers Screen
Amplifier Driver
Audio Video
Channel Selector

What's the point?

If you're still with me, you're my favorite person ever.

By breaking a device down into pieces or modules, the device becomes easier to understand and design. Drawing boxes around things is important. If you look at engineering design methods, management methods, and other aspects of organization, you'll see that most of the time, each method is just another way to draw boxes around things.

It also makes parts of a system easy to change. Does your TV need more than 13 channels? Change its channel selector/tuner. Is your screen larger than before? Change the video driver. Everything else can either stay the same or require a little change in the attached modules to accommodate it.

People can be systems, too. We're complex systems, so it's easier to look at one subsystem of ourselves at a time, like in this diagram from the Hacker's Diet.

Hacker's Diet
Hacker's Diet

Using this method, you can simplify and ease your life. It's easier to think of eating as fueling a machine when losing weight than to think of cake as delicious. Mentally, you have to draw a box around it.

I know I'm the type of person who will obsess over a project I start. This means that if I'm making good progress on my project at work, I won't stop. I'll continue working on it at home, and it'll start to infest my dreams. It starts to destroy the other parts of my life.

I've taught myself to draw a box around work, and I put that in a different subsystem. Only "Office ContraPants" can interact with the project. The rest of my personality can't see or interact with the project. There's a system boundary there.

Similarly, I'm not going to talk about politics at work. Only "Friends & Family ContraPants" knows about those things. Similarly, he doesn't know about my home projects, either.

Only "Late-Night ContraPants" writes articles for the Internet. After reading for a while or looking through project pictures, he writes this half-coherent tripe for War On Pants as a way to unwind for the rest of us.

This is just a nerdy engineering example of ideas I've seen on Zen Habits. Again, my method of easing my life is just another way to draw boxes around things. More people think in terms of a system diagram. I tend to think more like a layer diagram. Others seem to think of them as complex. Find something that works for you.

Boundaries are important. They keep my mind sane and my stress low. I may freak out at work, but I try to leave it at work. Boundaries hold back miasma and help prevent it from spreading to other people and other aspects of your life.

pbp-boundaries-fn1 I'm using an analog TV in my example. QAM channels and multiple-access methods are way beyond the scope of this article.

pbp-boundaries-fn2 This layer diagram isn't actually valid. Layer diagrams are more for showing what depends on what. A food chain would be a better example than a TV set, but this is what I was working on at the time.