What makes it clear to me is a fuller quote from Eric Raymond: "Even the simplest procedural logic is hard for humans to verify, but quite complex data structu

What makes it clear to me is a fuller quote from Eric Raymond: "Even the simplest procedural logic is hard for humans to verify, but quite complex data structures are fairly easy to model and reason about. To see this, compare the expressiveness and explanatory power of a diagram of (say) a fifty-node pointer tree with a flowchart of a fifty-line program. . . . "Data is more tractable than program logic. It follows that where you see a choice between complexity in data structures and complexity in code, choose the former. More: in evolving a design, you should actively seek ways to shift complexity from code to data." --- http://www.catb.org/~esr/writings/taoup/html/ch01s06.html http://www.catb.org/~esr/writings/taoup/html/ch01s06.html To paraphrase with a modern example, imagine a thousand lines of JSON, with deep nesting and all kinds of fields. It would still be easy to understand. Even a nonprogrammer could read it and find the part he's looking for (say, someone's address). Compare that to a thousand lines of procedural C code, or even a thousand lines of Python. That would be much harder, and your nonprogrammer friend would throw up his hands and walk away. The thing you hopefully learn after years of programming is that you can trade the length of one for the other. That is to say, you could simplify the JSON into half its length, if you make the code that processes it more complicated. Or you could simplify your procedural code by storing more complexity in your JSON data structure. The advice is to do the second thing, "to shift complexity from code to data." Also, from another chapter: "Data-driven programming is sometimes confused with object orientation, another style in which data organization is supposed to be central. There are at least two differences. One is that in data-driven programming, the data is not merely the state of some object, but actually defines the control flow of the program. Where the primary concern in OO is encapsulation, the primary concern in data-driven programming is writing as little fixed code as possible. Unix has a stronger tradition of data-driven programming than of OO." --- http://www.catb.org/~esr/writings/taoup/html/ch09s01.html http://www.catb.org/~esr/writings/taoup/html/ch09s01.html