Principle 20

... "an architecture of a specific system [is] a collection of computational components—or simply components-—together with a description of the interactions between these components—the connectors... An architectural style, then, defines a family of such systems in terms of a pattern of structural organization.  More specifically, an architectural style determines the vocabulary of components and connectors that can be used in instances of that style, together with a set of constraints  on how they can be combined... Given this framework, we can understand what a style is by answering the following questions:

(1) What is the structural pattern—the components, connectors, and constraints?

(2) What is the underlying computational model?

(3) What are the essential invariants of the style?

(4) What are some common examples of its use?

(5) What are the advantages and disadvantages of using that style?

(6) What are some of the common specializations?"

(David Garlan, Mary Shaw. An Introduction to Software Architecture, 1994)