Up to this point, we have pursued an approach of reverse engineering; we have assumed that we have the system in front of us and we are trying to understand what the system is (form) and how it works (function). In Chapters 4 through 6 we did this with simple systems (pump, bubblesort, bread slicing, and so on) to work through the approaches of system architecture before complicating the picture with systems of realistic complexity. But frankly, using these techniques of system architecture on systems as simple as bubblesort and a pump is like taking a sledge hammer to a thumb tack.

It is not possible to understand all of system architecture from such simple systems examined from a reverse engineering perspective. Therefore, we will now shift to an approach of ­“forward engineering,” in order to introduce two important ideas: solution-neutral function (Section 7.1) and concept (Section 7.3). In addition, we will introduce two systems of higher complexity: an air transportation service and a home data network. The air transportation service was chosen specifically to demonstrate how system architecting applies to the design of services. The home data system is a microcosm of global information networking.

In this chapter, we will introduce one new guiding question and begin to collate the questions from Chapters 4 through 6 into a method. Note that we modify some previous questions with new information, as shown by the brackets in Table 7.1.

We begin by introducing concept as a notion or shorthand that explains the system in brief. Let’s use the simple system of a corkscrew from Chapter 6. A corkscrew opens a wine bottle, but can we name other concepts for opening a wine bottle?

How would we describe a corkscrew in a general fashion? A corkscrew uses a screw to pull the cork. Surely, this is not the only way to open a bottle. If we get creative, we might think of other methods to “pull” the cork. We might glue a tab to the top of the cork and pull on the tab. We could potentially open the bottle without even touching the cork, by creating suction on the cork: surrounding it with a lower-pressure environment. While we’re thinking about using a pressure differential to remove the cork, we might consider pressurizing the air inside the bottle. This solution is actually sold as a household product, complete with a thin, hollow needle to pierce the cork, and a hand air pump. Alternatively, the wine steward in fine restaurants will sometimes use a fork-like device to pull on the sides of (shear) the cork.

Possible concepts for removing a wine bottle cork are shown in Figure 7.1, where we describe the concepts in a structured way as an operand-process-instrument set— for example, cork ­(operand) pushing (process) injected gas (instrument object).

This simple example illustrates a profound idea that we call solution-neutral function. ^[1] Solution-neutral function is the function of a system stated without reference to how the function is achieved. Box 7.1 explains this idea and its benefits.

In Figure 7.1, we described the solution-neutral function of our system as a “cork translating” and then specialized the cork translation function into cork pushing, shearing, and pulling. Note that there is more than one possible instrument object per specialized function; “pulling” alone is insufficient to describe the concept. A concept that specializes cork translating is “cork pulling with a screw”—a corkscrew.

There are a number of advantages associated with this structured representation of concepts, and chief among them is that it stimulates us to think about alternative specialized functions. For example, pulling led us to think about pushing the cork. Drawing the diagram of Figure 7.1 is one approach to structured creativity, which we will discuss in Chapter 12.

Solution-neutral function exists in a hierarchy, as shown in Figure 7.2. Translating the cork generalizes to removing the cork, but we could also destroy the cork by burning or melting it. Removing the cork generalizes to opening the bottle, which also specializes to breaching the cork (drilling a hole in it) or breaking the bottle to get at the wine. The highest level shown is accessing the wine. In Figure 7.2, we have omitted the associated instrument object in order to fit all the solution-neutral functions on one diagram: the corkscrew for pulling, the blowtorch for melting the cork, the table edge for breaking the bottle, and so on.

The breadth of concepts we generate is heavily dependent on the functional intent we pose. In this case, cork removing leads us to a narrower set of solutions than wine accessing. All else being equal, the more solution-neutral our expression of the functional intent of the system, the broader the set of concepts we will develop.

We have to choose where in the hierarchy of solution-neutral function to be. We could have continued upward to drink providing in the diagram, but there is the matter of practicality to consider. This is a question of functional intent. If we have a wine bottle on the table, it does not make sense to consider concepts that sit above wine accessing.

Having introduced the three key ideas of concept, solution-neutral function, and functional intent, let’s proceed to define each idea more rigorously in the context of higher-complexity systems.