The Software Development Requirement Document is a document to provide documentation which will be used to aid in software development by providing the details for how the software should be built. Within the Software Design Document are narrative and graphical documentation of the software design for the project including use case models, sequence diagrams, collaboration models, object behavior models, and other supporting requirement information.
The document contains all preparations pertaining to the development of each unit or module, including the software, test cases, test results, approvals, and any other items that will help to explain the functionality of the software.  The document is dynamic and is maintained by the system development team and should he constantly updated as the system’s development progresses.