SRS is the reference for the product architects to come out with the best
architecture for the product to be developed.Based on the requirements specified in SRS,usually more than one design approach for the product architecture is proposed
and documented in a DDS-Design Document Specification.
This DDS is reviewed by all the important stakeholders and based on various parameters as risk assessment,product robustness, design modularity,budget and time constraints,the best design approach is selected for the project.
A design approach clearly defines all the architectural modules of the project along with its communication and data flow representation with the external and third party modules(if any).The internal design of all the modules of the proposed architecture should be clearly defined with the minutest of the details in DDS.