Maximize composibility.

• Design components as though they were products (even though they are sometimes used only by other components).
• Minimize contextual requirements.
• Make each component communications-closed when possible -- a black box that does not communicate with anything else.
• Next best is relative closure -- guarantee the scope of communication (e.g., to other components within a common namespace.) Use authentication mechanisms and transaction control if necessary to enforce.
• Minimize preconditions
• Avoid side-effects outside the component.
• Minimize aliasing opportunities (where two references could refer to same object).
• Include means for a component to be exclusively controlled by others.
• Minimize commitment to control flow.
• Define services to be purely functional, stateless and preconditionless when possible.