Complexity (glossary)

(1) The degree to which a system's design or code is difficult to understand because of numerous components or relationships among components (ISO/IEC 2009)

(2) Consisting of interdependent, diverse entities that respond to their local and global environments (Page 2009)

Source

(1) ISO/IEC. 2009. "Systems and Software Engineering Vocabulary (SEVocab)" - ISO/IEC 24765. in International Organization for Standardization (ISO)/International Electronical Commission (IEC) [database online]. Geneva, Switzerland, 2009 [cited December 21 2009]. Available from http://pascal.computer.org/sev_display/index.action.

(2) Page, S. E. 2009. Understanding Complexity. The Great Courses. Chantilly, VA, USA: The Teaching Company.

Discussion

The first definition pertains primarily to systems that are difficult to understand, that is, the human perception of a system. This is often called behavioral or subjective complexity.

The second definition pertains to the system itself, the relationship between the elements and its properties. This is often called objective or structural complexity. Scott Page is a recognized authority on complexity.