Principles of Complex Systems for Systems Engineering
Sheard, S. A. & Mostashari, A. 2008. Principles of Complex Systems for Systems Engineering. Systems Engineering, 12, 295-311.
Overview System Concepts
This reference gives a very good oveview of the different perspective of complexity form both the hard objective and soft subjective perspectives.
it also attempts to provide a conceptual framework for complexity which will add significantly to the knowledge in this area when complete.