Ordinarily, Vision strips any trailing dot extension (such as .dat) from the logical name of a data file when generating file names for index and data segments (except for the first data segment). Setting V_STRIP_DOT_EXTENSION to 0 (off, false, no) allows you to prevent file extensions from being removed.
For example, the default first index segment name for the logical file file.001 is file.vix, which can cause problems if you also had a file called file.002. When V_STRIP_DOT_EXTENSION is set to 0, the index segment name becomes file.001.vix.
V_STRIP_DOT_EXTENSION is set to 1 (on, true, yes) by default.