*simple*would be simple to define. But there is no widespread agreement on what the words related to complexity mean.

So in this blog, I am going to define some of the terminology that is important in IT complexity reduction. I won't claim that these meanings are relevant to all fields, but when I use these words, this is what they will mean. This is my initial pass. I will give examples from my own work, since that is the domain with which I am most familiar.

I invite readers to comment. Soon I will consolidate the discussion into a terminology proposal for www.cuec.info (The Consortium for Untangling Enterprise Complexity.) I assume that better definitions will come out of this discussion.

**Simplicity Framework**: A simplicity framework is an approach, model, or methodology that seeks to find, measure, and remove complexity from some domain. Any simplicity framework should specify the domain for which it is intended. Example: SIP (Simple Iterative Partitions) is a

*simplicity framework*for IT architecture.

**Complexity**: Complexity is a measure of an attribute of a system that makes that system difficult to understand, manage, and/or implement. Complexity is measured in some units appropriate for the domain and defined by a simplicity framework. Example: In SIP,

*complexity*is measured in Standard Complexity Units (SCUs).

**Solution Set**: For some problem P in a given domain, the solution set is the set of all solutions that solve P. Note that a solution set only includes

*solutions*to P. If a proposed solution would not solve P, then it is by definition not a member of the solution set. Example: When considering architectures for an inter-library loan system, we examined dozens of potential candidates from the

*solution set*.

**Simple Solution**: A simple solution is the element of a solution set that has the least complexity of all elements in the solution set. Note that it is theoretically possible that more than one solution from the solution set share the lowest complexity. In this case, there are multiple simple solutions. Example: People were surprised that the

*simple solution*to the inter-library loan system was not the one initially proposed.

**Complex Solution**: A complex solution is any of the elements of the solution set that are not the

*simple solution*and whose complexity can be reduced through the

*simplicity framework*. Example: In the inter-library loan system, all of the originally proposed SOA architectures were

*complex solutions*.

**Simplistic Solution**: A simplistic solution is any proposed solution to a problem that lacks the minimum complexity necessary to solve that problem. By definition a simplistic solution is not a member of the solution set. Example: The catalog system we looked at turned out to be a

*simplistic solution*to the inter-library loan system.

**Chaotic Solution**: A chaotic solution is a solution that is presumed to solve a problem, but whose complexity is so high that using (or continuing to use it) is not feasible and reducing it is not practical given the simplicity framework. Note that it is not always possible to determine if a chaotic solution is even a member of the solution set. Example: The present inter-library loan system is a

*chaotic solution*.

Do you have any ideas for more terms that should be defined? Do you have issues with these definitions? Leave comments here or discuss with me on Twitter (@RSessions). And keep an eye on www.cuec.info for efforts to standardize some of these terms.

**Planned Version 2 Changes:**

@johanlindberg suggested using

*candidate*to describe Simplistic and Chaotic. His argument: Simplistic and Chaotic are by definition not solutions. Good point! He also suggested giving comparison terms to show similar terms in complexity theory and SW development.

@HotFusionMan (Al Chou) suggested adding note about layers of complexity. I think this is a detail of the simplification framework, but I need to make clear the generic character of these definitions.

Add definitions for simplicity, simplification. Add description of which problem spaces these definitions are appropriate for (those that are striving for simplicity.) Make less specific to IT and general to any situation in which a move from complex to simple is desirable.

Incorporate Nikos's discussion on understandability.

And thanks to @JohnDCook for Twitter contributions!