18.5 Summary

Quality attributes can be maintained in a system, even if that system is largely integrated from off-the-shelf components whose design and interaction mechanisms are not under the architect's control. However, achieving quality attributes in this type of system requires significantly different practices than for custom-developed code. The requirements process needs to be more flexible, allowing what is available in the marketplace to modify requirements to provide a better overall business solution. Essential requirements need to be identified and introduced as a critical constraint in the evaluation of feasible component ensembles. Multiple contingencies need to be considered, and as essential requirements increase in number and difficulty, custom development must be considered as a fallback.