The old approaches for establishing software traceability are performed manually or using some static tools to form forward traceability only - the results are not accurate and not precise, and hard to maintain.
        Differently, with NSE the traceability is established dynamically through test case execution - the obtained results are accurate, precise, bi-directional, and self-maintainable: when the test cases or the source code is modified, after re-executing the test cases, new accurate, precise, and bi-directional traceability will be automatically re-built. This bi-directional traceability is the base for quantitative software engineering and the support for the implementation of requirement changes or code modification with side-effect prevention. .
        This bi-directional traceability can be extended to include all related models and documents using some keyword (such as @HTML@, @WORD@, @PDF@, @EXCEL@, and @BAT@)) written in the test case description part to indicate the format, the file path, and the bookmark of a document/model for automatically opening it from the detailed location specified by the bookmark (about the detailed application examples, see section (9) "Responding to requirement changes in maintenance") . A simple application example is shown as follows: