System

STATUS: DRAFT
I need to revise this definition of "System" to fit with the "SoftwareSystem" page.
A system is a set of interacting components.
The form/context division is interesting; I'll need to think about how to fit that in.

A system is something that has an inside and an outside (its Context). A system is defined by the Boundary between inside and outside. The system communicates with its context by passing Messages back and forth. A system may have internal State.

It is arguable whether systems are arbitrary constructs superimposed on a continuous reality, or whether they exist objectively in some sense. An argument for objectivity is that, given a universe of interacting entities, we can draw certain boundaries that are crossed by simpler patterns of messages than others, implying that the systems so defined are more coherent—more "system-like". An argument for subjectivity is that there is nothing, in theory, that prevents us from dividing up the universe into systems in any way we choose.

In NotesOnTheSynthesisOfForm

ChristopherAlexander uses the term ensemble to refer to what I'd call a system: the union of a designed Form and its Context. He emphasizes that the division between form and context is not unique:

We must also recognize that no one division of the ensemble into form and context is unique. Fitness across any one such division is just one instance of the ensemble's internal coherence. Many other divisions of the ensemble will be equally significant. Indeed, in the great majority of actual cases, it is necessary for the designer to consider several different divisions of an ensemble, superimposed, at the same time. —p. 12

This is also true of software: at the Boundaries between Components there is often DeepInterlockAndAmbiguity, and depending on what we're using the model for it may make more sense to associate the boundaries with the form or the context.

Alexander also points out that the form-context division can be applied recursively:

Indeed, the form itself relies on its own inner organization and on the internal fitness between the pieces it is made of to control its fit as a whole to the context outside. —p. 18