Design approaches for taming complexity

We examine the essential characteristics of system complexity and simplicity and we describe a set of general design heuristics to address complexity. We distinguish inherent, irreducible complexity from perceived complexity. We illustrate a little theory of complexity with examples drawn from ultra-large-scale systems: telephony, the Internet, and the power grid. We then show how a toolkit of design approaches that have been developed by system and software architects over the last 15 years can tackle complexity. In particular, architectural patterns and tactics provide systematic means to reduce and manage complexity, both intrinsic and perceived.