In the statements @GET, @SAVE, @READ, @WRITE (format 2), @OPEN (format 2), @ELIM, @INPUT (Format 2), @FILE and @UNSAVE it is possible, in addition to the file name, to specify a version number between 0 and 255 or specify * to represent the current version number. This makes it possible to protect the file against accidental overwriting.
When a file is first created, it is assigned the version number 1 after being written to disk. Each time the file is written, DMS increases the version number by 1.
The version number is incremented up to 255. The following version number is then 0 again.
Read accesses (@GET, @READ) with a version number other than the current version number are executed. The current version number is output in message EDT0902.
If * is specified as the version number then the current version number is also displayed in the message EDT0902. Although this specification is possible in @INPUT (format 2), it is completely ignored. Write accesses (@SAVE, @WRITE (format 2), @ELIM, @UNSAVE)
and attempts to open files for real processing (@OPEN, format 2) with a version number other than the current value are not executed. Instead, the correct version number is displayed in the message EDT4985.
In the case of the explicit or symbolic specification of the current version number, the new version number which has been incremented by 1 is displayed in the message EDT0902.
The version numbers provide increased protection against file destruction. If a version number is specified when a file is read in, then the valid version number is output after the read operation, thus making it possible to identify obsolete file versions.
The EDT version number should not be confused with the generation number of file generation groups in BS2000. This is a component of the file name.
For each generation, it is also possible to specify a version number.
The meaning of the EDT version number corresponds more closely to the variant number of library elements.