Chapter 5: The Second System Effect

The second-system effect proposes that, when an architect designs a second system, it is the most dangerous system they will ever design, because they will tend to incorporate all of the additions they originally did not add to the first system due to inherent time constraints. Thus, when embarking on a second system, an engineer should be mindful that they are susceptible to over-engineering it (*).


Adde parvum parvo magnus acervus erit.
{Add little to little and there will be a big pile.}

Ovid


If one separates responsibility for functional specification from responsibility for building a fast, cheap product, what discipline bounds the architect’s inventive enthusiasm?

The fundamental answer is thoroughgoing, careful, and sympathetic communication between architect and builder. Nevertheless there are finer-grained answers that deserve attention.


Interactive Discipline for the Architect

When a construction architect devises a project against a budget, it usually happens that the initial offer has to be re-designed iteratively in order to fit contractor’s bids.

An analogous process governs the architect of a computer/programming system, with the advantage of getting bids from the contractor at many early points in his design, almost any time he asks for them. He usually has the disadvantage of working with only one contractor, who can raise or lower his estimates to reflect his pleasure with the design. In practice, early and continuous communication can give the architect good cost readings and the builder confidence in the design without blurring the clear division of responsibilities.

The architect has two possible answers when confronted with an estimate that is too high: cut the design or challenge the estimate by suggesting cheaper implementations. This latter is inherently an emotion-generating activity. The architect is now challenging the builder’s way of doing the builder’s job. For it to be successful, the architect must

  • be aware that he suggests, not dictates : the builder has the inventive and creative responsibility for the implementation
  • be flexible and always be prepared to suggest a way of implementing anything he specifies, and be prepared to accept any other way that meets the objectives as well
  • deal quietly and privately in such suggestions
  • be ready to forego credit for suggested improvements


Self-Discipline — The Second-System Effect

When an architect first designs a work, it starts from the ignorance of not knowing what is to be done, so he pays careful attention, controlling every aspect, taking out concepts and feature not really relevant, but stores them for a future when they might be used.

The architect faces no a second system to design, which is the most dangerous system a man ever designs. When he does his third and later ones, his prior experiences will confirm each other as to the general characteristics of such systems, and their differences will identify those parts of his experience that are particular and not generalizable.

The general tendency is to over-design the second system, using all the ideas and frills that were cautiously sidetracked on the first one. The result, as Ovid says, is a “big pile” of functionalities where most of them are rarely used.

The second-system effect has another manifestation somewhat different from pure functional embellishment. That is a tendency to refine techniques whose very existence has been made obsolete by changes in basic system assumptions.

How does the architect avoid the second-system effect? Well, obviously he can’t skip his second system. But he can be conscious of the peculiar hazards of that system, and exert extra self-discipline to avoid functional ornamentation and to avoid extrapolation of functions that are obviated by changes in assumptions and purposes.

A discipline that will open an architect’s eyes is to assign each little function a value: capability x is worth not more than m bytes of memory and n microseconds per invocation. These values will guide initial decisions and serve during implementation as a guide and warning to all.

How does the project manager avoid the second-system effect? By insisting on a senior architect who has at least two systems under his belt. Too, by staying aware of the special temptations, he can ask the right questions to ensure that the philosophical concepts and objectives are fully reflected in the detailed design.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s