Requirements tracing

The source module hello.c on the left has versions zero through four. The design document hello_dsn.c on the right has versions zero through three. Three hyperlinks named DesignDoc are shown starting on the left and extending to the right. The first hyperlink connects version 2 of hello.c with version 2 of hello_dsn.c. The second hyperlink connects version 3 of hello.c with version 3 of hello_dsn.c. The thirds hyperlink is attached to version 4 of hello.c but is null-ended.