General principles of systems design

is an excellent book edited by Jerry Weinberg (isbn 0-932633-07-2). As usual I'm going to quote from a few pages:

It's not the appearance that's the essence of their structure, it's their endurance. Structure is that which stands, which remains, which is unchanged, regardless of its physical properties.

No answer can be both precise and general at the same time.

Aggregation gives protection against the unknown; specialization against the known; and the use of each sacrifices some opportunity to use the other.

The concept of structure... derives from the concept of stability, and not vice versa.

Any representation of a system tends to make certain insights easier at the expense of making others harder.

Failing to yield is the only clue we have to the existence of structure... we can only understand permanence through attempts to change it.

When a system has to deal simultaneously with two threats, protection against one will increase vulnerability to the other.

This conception of the relationship between structure and behaviour is utterly contrary to the most widely held view - namely that structure determines behaviour.

The system responds more slowly in order to respond more surely.

The regulator must be active so that other parts may be passive.

Regulation is invisible - when it works.

Complexity is a relationship between system and observer.

Not only do birds regulate the insect population, but the insects return the favour for the birds.

There is a tendency for complexity in models to rise as the time between sensing and acting grows.