Identify and encapsulate commonality and variability.

• Find, isolate, and implement means of handling expected variability, while capturing common invariants in a single component specification.
• Define the ``domain of applicability'' (solution space) of the component.
• Basis for isolating components
• Basis for interface abstraction and refinement
• Basis for configuration specification -- components may be parameterized to adapt to different contexts
• Must find common design decisions/functionality in order to code and use it.
• Generalizing components to handle variability enhances reuse.
• Does it matter if you look for commonality or variability first?