Systems

A system: set of related elements that perform a job. An element cannot perform the desired job by its own

An architecture of a system is fundamentally concerned with how a system is organized into its constituent elements and how these elements relate to each other to achieve a given purpose
(Bass et al., 2003)

Architecture is fundamentally concerned with the organization of a system into its constituent elements and their interrelationships to achieve a given purpose.

Complexity:

• Dependencies
• Incidental complexity: complexity that cannot be avoided
• Accidental complexity: complexity that can be avoided 

Thinking in systems 

Traditional thinking breaks down a systems into small components, then design and build each components in isolation. When you integrate these components, the entire systems could not be cost-effective. However, systematic thinking focuses on a component while remembering that it's a crucial par of the bigger system.