Meditations On Emergence

Emergence is the phenomenon referred to in phrases like EmergentBehavior and EmergentDesign.

From the American Heritage Dictionary:

emerge: (4) To come into existence. [http://www.dictionary.com/cgi-bin/dict.pl?term=emerge&db=*]

emergence: (1) The act or process of emerging. [http://www.dictionary.com/cgi-bin/dict.pl?term=emergence&db=*]

For the purposes of this Wiki, there seem to be three important questions about the phenomenon of emergence:

1. What is it?

Emergence is the existence in a system of a property, characteristic or behavior that is not a property, characteristic or behavior of any of the constituents of that system.

2. How does it happen?

Emergence arises due to the interactions of the constituents of a system, either among themselves alone, or in concert with external entities.

3. What are its implications for software development?

Many (most?, all?) types of emergence exhibit a curious characteristic: simple changes at the level of the constituents of a system generate complex results at the level of the system as a whole.

The design of any but the simplest of software systems is inherently complex. Yet it has been stated that consistent application of the rules of code quality advocated by ExtremeProgramming yields well-formed software design, even though these rules are themselves quite simple.

For example:

"What is interesting - I claim - is the extent to which good design is the emergent result of the rules of code quality in XP Explained:

1, Runs all the tests.

2. Expresses all the ideas you want to express.

3. Contains no duplicate code.

4. Contains minimum number of classes and methods."

- Ron Jeffries, 10/31/2000 [http://www.egroups.com/message/extremeprogramming/14813]

This phenomenon of EmergentDesign, which seems to be an essential feature of ExtremeProgramming, warrants further thought and investigation.

EmergentDemocracy? can be found at: http://joi.ito.com/static/emergentdemocracy.html

the paper was written in a process that included a wiki.

StephenWolfram's A NewKindOfScience discusses emergence; whether or not it's the "bottom line" on emergence is debated.