6.1 When describing a system, explain why you may have to design the system architecture before the requirements specification is complete.

The architecture may have to be designed before specifications are written to provide a means of structuring the specification and developing different subsystem specifications concurrently, to allow manufacture of hardware by subcontractors and to provide a model for system costing. You may have to design the system architecture before the requirements specification is complete because the architecture has a significant impact on the non-functional requirements and can also influence the functional requirements as well. Specifically, in order to demonstrate to stakeholders that an application will meet its performance requirements a project manager or system architect may have to show how the architecture will aid in accomplishing this goal. According to Sommerville the components affect the requirements and therefore an architecture that explains the components and their relationships may aid in the determination of the requirements. System architecture is to be designed first before describing the system itself simply because the architectural design serves as basis for the description. Since it involves identifying major system components, subsystems, and their communications, it will be easier in the description to specify which one goes to which subsystems. When subsystems are already made, it will be easier to determine what components are needed by hard are manufacturers. So, the architectural design provides a model for system costing.