An ISAM file is opened for real processing using the @OPEN statement (format 2). If the file does not yet exist, it is created before being opened. When this is done, the default attributes for ISAM files are used unless a different specification has been made using the fixed file link name EDTMAIN. The file remains open until processing is terminated by means of an explicit or implicit close.
If the file link name EDTMAIN is used, it is still necessary to specify the file name in the @OPEN statement. It is not possible to specify '/'.
The real processing of ISAM files with non-standard key positions or key lengths longer than the default value is not supported.
The real processing of ISAM files with duplicate key values or non-numerical keys is not supported. If such a file is opened then an error occurs as soon as one of its records is processed.
If a file's key length is shorter than 8 (or 16 in the case of UTF16 files) then the line number is left-filled with zeros when read in. For example, in the case of a KEY-LENGTH specification of 4, the ISAM key 1234 would be taken over as line number 0000.1234. Furthermore, in this case the current increment would be set to a suitable value. If when the file is opened, the current increment has the default value 1 or if the set increment is greater than the largest possible line number then it is set to the value 0.0001 for key lengths smaller than or equal to 2, to 0.01 for key lengths smaller than or equal to 5 and to the value 1.0 otherwise.