Definition of file attributes

BS2000 provides the CREATE-FILE command for creating files. A task file table entry with further file attributes is created by means of the ADD-FILE-LINK command. The complete format for this command and a detailed description are provided in “Commands” manual [3] and “Introductory Guide to DMS” [4].

Catalog entry

When file attributes are defined with the CREATE-FILE command it must be ensured that the primary memory allocation is sufficient.
This is particularly true in the case of files in which the block size exceeds the primary allocation which the operating system assumes by default. The block size is calculated from the specification in the COBOL program (see “COBOL2000 Reference Manual” [1]). If the COBOL program yields a block length of (STD, n), the PRIMARY-ALLOCATION in the SPACE operand of the CREATE-FILE command should be at least

• 2n for sequential files.

• 2n+2 for indexed and relative files.

Task file table (TFT)

Whenever a ADD-FILE-LINK command with the operand

LINK-NAME=linkname

is issued for a file, the DMS creates an entry for the file under this link name in the task file table (TFT) and stores all file attributes explicitly defined in the ADD-FILE-LINK command under this entry.

Each of these entries is retained in the TFT until it is

• removed by a REMOVE-FILE-LINK command for the assigned file link name, or deleted together with the TFT at the end of the task, or

• overwritten by a new ADD-FILE-LINK command for the same file link name.

Information on the current contents of the TFT can be obtained by using the SHOW-FILE-LINK command.

When a COBOL program attempts to open a file, the DMS first checks whether the TFT contains the link name that was defined for the file at compilation (see section "Assignment of cataloged files"). If such an entry is found, the program takes over file attributes from

• the TFT entry under this link name,

• the file attributes that were explicitly or implicitly specified in the program, and

• the catalog entry of the associated file.

The specifications from the TFT entry (i.e. file attributes explicitly defined in the ADD-FILE-LINK command) overwrite file specifications from the COBOL program. The catalog entry is referred to only for file attributes that are defined neither in the program nor in the TFT entry or those that were specified as null operands in the ADD-FILE-LINK command.

This approach could lead to conflicts during file access, especially when file attributes specified in the ADD-FILE-LINK command are not compatible with the (explicitly or implicitly) defined characteristics in the COBOL program or in the catalog entry of the assigned file. This is especially applicable in the following situations:

• Conflicting entries on the open mode

  COBOL program	ADD-FILE-LINK command
  OPEN INPUT...[REVERSED]	OPEN-MODE=OUTPUT or OPEN-MODE=EXTEND
  OPEN OUTPUT	OPEN-MODE=INPUT or OPEN-MODE=REVERSE
  OPEN EXTEND	OPEN-MODE=INPUT or OPEN-MODE=REVERSE

• Conflicting entries on the organization type of the file

  COBOL program	ADD-FILE-LINK command
  ASSIGN clause ORGANIZATION clause	ACCESS-METHOD operand

• Conflicting entries on the record format

  COBOL program	ADD-FILE-LINK command
  RECORD clause RECORDING MODE clause	RECORD-FORMAT operand

• Conflicting entries on the record length

  COBOL program	ADD-FILE-LINK command
  RECORD clause record description entry	RECORD-SIZE operand

• Conflicting entries on the record key

  COBOL program	ADD-FILE-LINK command
  RECORD KEY clause record description entry	KEY-POSITION operand KEY-LENGTH operand

• Conflicting entries on the disk format or file format

  Catalog entry	ADD-FILE-LINK command
  BLK-CONTR = BUF-LEN =	BLOCK-CONTROL-INFO operand BUFFER-LENGTH operand

Example 9-4

Creating and displaying a TFT entry
(shown in BS2000/OSD V5.0)

 

/ADD-FILE-LINK INOUTFIL,ISAM.UPDATE, -                             (1)
/              BUFFER-LENGTH=*BY-CATALOG,                           | 
               SUPPORT=*DISK(SHARED-UPDATE=*YES)                   (1)
/SHOW-FILE-LINK INOUTFIL,INFORMATION=*ALL  ——————————————————————— (2)

LINK-NAME ————————— FILE-NAME —————————————————————————————————————————————
INOUTFIL            :N:$F2190202.ISAM.UPDATE
———————————————————— STATUS ———————————————————————————————————————————————
STATE      = INACTIVE    ORIGIN      = FILE
———————————————————— PROTECTION ———————————————————————————————————————————
RET-PER    = *BY-PROG    PROT-LEV    = *BY-PROG
BYPASS     = *BY-PROG    DESTROY     = *BY-CAT
———————————————————— FILE-CONTROL-BLOCK - GENERAL ATTRIBUTES ——————————————
ACC-METH   = *BY-PROG    OPEN-MODE   = *BY-PROG   REC-FORM   = *BY-PROG
REC-SIZE   = *BY-PROG    BUF-LEN     = *BY-CAT    BLK-CONTR  = *BY-PROG
F-CL-MSG   = STD         CLOSE-MODE  = *BY-PROG
———————————————————— FILE-CONTROL-BLOCK - DISK FILE ATTRIBUTES ————————————
SHARED-UPD = YES         WR-CHECK    = *BY-PROG   IO(PERF)   = *BY-PROG
IO(USAGE)  = *BY-PROG    LOCK-ENV    = *BY-PROG
———————————————————— FILE-CONTROL-BLOCK - TAPE FILE ATTRIBUTES ————————————
LABEL      = *BY-PROG   (DIN-R-NUM   = *BY-PROG,  TAPE-MARK  = *BY-PROG)
CODE       = *BY-PROG    EBCDIC-TR   = *BY-PROG   F-SEQ      = *BY-PROG
CP-AT-BLIM = *BY-PROG    CP-AT-FEOV  = *BY-PROG   BLOCK-LIM  = *BY-PROG
REST-USAGE = *BY-PROG    BLOCK-OFF   = *BY-PROG   TAPE-WRITE = *BY-PROG
STREAM     = *BY-PROG                      |
———————————————————— FILE-CONTROL-BLOCK - ISAM FILE ATTRIBUTES ————————————
KEY-POS    = *BY-PROG    KEY-LEN     = *BY-PROG   POOL-LINK  = *BY-PROG
LOGIC-FLAG = *BY-PROG    VAL-FLAG    = *BY-PROG   PROPA-VAL  = *BY-PROG
DUP-KEY    = *BY-PROG    PAD-FACT    = *BY-PROG   READ-I-ADV = *BY-PROG
WR-IMMED   = *BY-PROG
———————————————————— VOLUME ———————————————————————————————————————————————
DEV-TYPE   = *NONE       T-SET-NAME = *NONE
VSN/DEV    = PUBN03/D3480

(1)

The ADD-FILE-LINK command assigns the link name INOUTFIL to the file ISAM.UPDATE and defines that the value from the catalog entry for ISAM.UPDATE will be assigned for the BUFFER-LENGTH operand when the file is opened, and SHARED-UPDATE=YES, i.e. ISAM.UPDATE can be updated by more than one user simultaneously (see section "Shared updating of files (SHARED-UPDATE)"). The DMS creates a TFT entry under the name INOUTFIL and stores these specifications in it.

(2)

The SHOW-FILE-LINK command outputs the contents of the TFT entry for INOUTFIL with the operand values. Note that the values BUF-LEN = *CAT and SHARUPD = YES are derived from the specifications in the ADD-FILE-LINK command. The remaining operands were not explicitly defined and thus have the default values *BY-PROG or *NONE.