A complex system is an arrangement of a great number of related but various elements with intricate relationships and interconnections. Complexity research is applied in a wide range of fields including software development, architecture, artificial intelligence, city planning, networking, bioinformatics and software engineering.
Complex systems typically have input from many sources and are highly changeable. In the physical world, the earth's weather is one example of a complex system. In technology, the Internet is a prime example of a complex system or perhaps a system of systems: A large and complex system composed of multiple, dispersed, independent systems. The burgeoning Internet of Things (IoT) adds complexity as it develops by making it possible to gather data from and interact with an ever-increasing number of devices and objects, many of which can also communicate automatically with each other.
Chaos theory deals with the apparent lack of order and predictability in complex systems. Chaos, in this context, refers to an apparent lack of order in a system that nevertheless obeys particular laws or rules. The two main propositions of chaos theory are the idea that systems - no matter how complex they may be - rely upon an underlying order, and that very simple or small systems and events can cause very complex behaviors or events.