Processing with VSAM Files
Please use speaker notes for
additional information!
Organization is sequential
Access is sequential
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS SEQUENTIAL
ACCESS IS SEQUENTIAL.
This code means that the file is organized
without indexes and will be read sequentially
one record at a time. Note that since sequential
is the default for both organization and access,
these clauses do not need to be specified.
The organization of the tells how the data is organized. Organization sequential means that it is
organized without indexes. Organization indexed means that it is an indexed file with a primary
index and possible alternate indexes that can be used to access the records. Essentially that
means that there will be a data file and an index file used to access the data. The third type of
organization is relative which will be not be dealt with in this presentation.
Once a file has been set up with indexes, other programs reading or updating this file must also
specify the indexes. The indexes can then be used to access the records on the file. Today
indexed files are VSAM (Virtual Storage Access Method).
Access refers to how the records on the file will be accessed. The access method is directly
related to the organization. For example if the organization is sequential, the records can only be
accessed sequentially.
Organization is indexed
Access is sequential
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
This file is an indexed VSAM file. That means
that the records are stored on a disk using a
methodology that includes indexes. This means
that there will be two files: one containing the
data and one containing the indexes. The index
can be either numeric or alphanumeric. The
index must be unique so frequently a field like
social security number or some other
identification number is used as the index.
In this example, the file is organized so that it
has indexes. The field that is the index is
specified in the record key clause. The access
on this select is sequential which means that the
file will be read sequentially one record at a
time. Note that the indexed field that is the
record key must then be defined in the FILESECTION.
Organization is indexed
Access is random
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
With random access, the indexed structure can
be used to access a specific record based on the
record key.
The structure of the program usually involves
reading a transaction that contains a particular
identification number and then randomly
finding a match to that identification number in
the indexed file. (Note I used identification
number because that is the record key in the
example).
Organization is indexed
Access is dynamic
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS DYNAMIC
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
With indexed organization, you can also
specify that ACCESS IS DYNAMIC. This
means that the indexed file can be read both
sequentially and dynamically in this
program. For example, you might
randomly access a particular record and
then process the records after it in the file
sequentially until a particular condition is
met. As we will see, with dynamic access
the programmer must write code to specify
whether the read is random or sequential.
Alternate key
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO
ALTERNATE RECORD KEY IS EMPNAME
WITH DUPLICATES.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 EMPNAME
PIC X(20).
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS IDNO
ALTERNATE RECORD KEY IS EMPNAME
WITH DUPLICAT3S.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 EMPNAME
PIC X(20).
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS DYNAMIC
RECORD KEY IS IDNO
ALTERNATE RECORD KEY IS EMPNAME
WITH DUPLICATES.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 EMPNAME
PIC X(20).
Creating a VSAM file
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
WRITE INDEXED-REC
INVALID KEY
PERFORM B-300-ERROR-WRITE.
In this example, I am going to be creating
a indexed sequential file with IDNO as
the key. When dealing with indexes there
is the possibility that I will encounter a
situation where the write is invalid. In
these cases, the invalid key clause on the
write will be triggered. If the write is
invalid, the write will not be executed.
Instead processing will go to B-300ERROR-WRITE.
Write an indexed file
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO.
FD
01
WRITE INDEXED-REC
INVALID KEY
PERFORM B-300-ERROR-WRITE
NOT INVALID KEY
PERFORM B-310-PAPER-TRAIL
END-WRITE
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
There is also a NOT INVALID KEY
clause that allows the programmer to
specify activity that is to take place if
the WRITE was successful. For
example, the programmer could have a
routine that writes a report containing
all of the records successfully written tot
he file.
Note that the END-WRITE clause can
be used with the WRITE as well.
Creating an indexed file
SELECT SEQ-PAY-FILE
ASSIGN TO “A:\PAYORIG.DAT”
ORGANIZATION IS SEQUENTIAL
ACCESS IS SEQUENTIAL.
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO.
DATA DIVISION.
FILE SECTION.
FD PAYORIG
DATA RECORD IS PAYIN-REC.
01 PAYIN-REC.
05 ID-IN
PIC 9(5).
05 REST-IN
PIX X(100).
FD INDEXED-FILE
DATA RECORD IS INDEXED-REC.
01 INDEXED-REC.
05 IDNO
PIC 9(5).
05 REST-DATA PIC X(100).
B-200-LOOP.
MOVE ID-IN TO IDNO.
MOVE REST-IN TO REST-DATA.
WRITE INDEXED-REC
INVALID KEY
PERFORM B-300-WRITE-ERR.
READ PAYORIG
AT END
MOVE “NO “ TO MORE-RECS.
Reading an indexed file sequentially
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
READ INDEXED-FILE
AT END
MOVE “NO “ TO MORE-RECS.
When an indexed file is being read sequentially the
usual sequential read is used. Essentially, you can
read the indexed file sequentially from record one
until end of file has been reached. The processing
will be the same as if the organization was
sequential.
EQUAL TO
=
GREATER THAN
START filename KEY IS
>
NOT LESS THAN
NOT <
GREATER THAN OR EQUAL TO
>=
In this example, I have the user
INVALID KEY…
enter an identification number
NOT INVALID KEY…
which is accepted to an area in
END-START
working storage. The entered
DISPLAY “ENTER START IDNO”.
number is then moved to IDNO
ACCEPT IDNO-ENTERED.
which is the RECORD KEY. I
MOVE IDNO-ENTERED TO IDNO
then look for a starting point
START INDEXED-FILE
based on the KEY >= to IDNO.
KEY >= IDNO
If the user entered 45678 then
INVALID KEY
processing would start with
DISPLAY “INVALID START POINT”
either 45678 or the first record
MOVE “NO “ TO FOUND-IND
larger than 45678. If no record
NOT INVALID KEY
was equal or greater than other
MOVE “YES” TO FOUND-IND
processing needs to be coded.
END-START
NOTE: The START positions, a
IF FOUND-IND = “YES”
READ is needed to actually read
READ INDEXED-FILE
the record.
AT END
MOVE “NO “ TO MORE-RECS.
START verb
Sequentially reading using alternate key
When you want to read sequentially
along the alternate key path, you use
the START verb to establish both the
alternate key path and the starting
point. In this example, I want to read
the starting with the first record along
the alternate key path. To do this, I
move LOW-VALUES to the field
defined as the ALTERNATE RECORD
KEY and then in the KEY clause of the
START, I again use the name of the
ALTERNATE RECORD KEY. This
not only locates the record but also
establishes the path to be followed with
the sequential READ.
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS SEQUENTIAL
RECORD KEY IS IDNO
ALTERNATE RECORD KEY IS EMPNAME
WITH DUPLICATES.
FD INDEXED-FILE
DATA RECORD IS INDEXED-REC.
01 INDEXED-REC.
05 IDNO
PIC 9(5).
05 EMPNAME
PIC X(20).
MOVE LOW-VALUES TO EMPNAME.
START INDEXED-FILE
KEY GREATER THAN EMPNAME
INVALID KEY
...
READ INDEXED-FILE
AT END
MOVE “NO “ TO MORE-RECS.
Random read - record/prime key
MOVE TRAN-ID TO IDNO.
READ INDEXED-FILE
INVALID KEY
PERFORM B-310-PROBLEM
NOT INVALID KEY
PERFORM B-300-PROCESS
END-READ
OR
MOVE TRAN-ID TO IDNO.
READ INDEXED-FILE
INVALID KEY
PERFORM B-310-PROBLEM.
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS IDNO.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 ...
MOVE TRAN-ID TO
IDNO establishes the key.
The READ that randomly
reads the file looking for a
record with that IDNO.
If the read is not successful
in finding a record with that
IDNO, the INVALID KEY
clause is executed.
Random read - alternate key
MOVE EMP-NAME-TRAN TO EMPNAME.
READ INDEXED-FILE
KEY IS EMPNAME
INVALID KEY
PERFORM B-310-PROBLEM
NOT INVALID KEY
PERFORM B-300-PROCESS
END-READ
OR
MOVE EMP-NAME-TRAN TO EMPNAME.
READ INDEXED FILE
KEY IS EMPNAME
INVALID KEY
PERFORM B-310-PROBLEM.
SELECT INDEXED-FILE
ASSIGN TO “A:\PAYROLL.DAT”
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS IDNO
ALTERNATE RECORD KEY IS EMPNAME
WITH DUPLICAT3S.
FD
01
INDEXED-FILE
DATA RECORD IS INDEXED-REC.
INDEXED-REC.
05 IDNO
PIC 9(5).
05 EMPNAME
PIC X(20).
The employee name from the transaction is
move to the EMPNAME to establish the
key. Since this READ is going to be using
the ALTERNATE RECORD KEY the KEY
clause has to be used in the READ to
establish the fact that we are searching for a
match in the alternate index, not the prime
index.
Read sequentially
&/or randomly
SELECT MASTER-FILE
ASSIGN TO "C:\PCOBWIN\VSAM\VSAMALT.DAT"
ORGANIZATION IS INDEXED
ACCESS IS DYNAMIC
RECORD KEY IS MID
ALTERNATE RECORD KEY IS MITEM-NAME WITH DUPLICATES.
This file is organized with indexes and the ACCESS IS DYNAMIC clause allows the programmer
to access the file either sequentially or randomly using either the record key MID or the alternate
record key MITEM-NAME.
Sequential read using primary key:
(Assumes starting point has been
established).
READ MASTER-FILE NEXT
AT END
MOVE "YES" TO EOF-IND
END-READ.
When reading a ACCESS IS DYNAMIC file
sequentially, the NEXT is required to
differentiate between the two types of READs.
Random read using primary key:
MOVE RETR-ID TO MID.
READ MASTER-FILE
INVALID KEY
PERFORM B-310-INVALID
NOT INVALID KEY
PERFORM B-300-PROCESS
END-READ.
Random and
sequential reads
MOVE START-PT TO MID.
MOVE "YES" TO MSTR-FOUND.
READ MASTER-FILE
INVALID KEY
MOVE "NO " TO MSTR-FOUND.
IF MSTR-FOUND = "YES"
PERFORM B-300-DETAIL
EOF-MSTR = "YES”.
B-300-DETAIL.
...processing...
READ MASTER-FILE NEXT
AT END
MOVE "YES" TO EOF-MSTR.
This code shows the START-PT being moved
to the MID (the record key) and then a random
read being done to locate the record that is
requested. When the record is found, control
will pass to the B-300-DETAIL.
In this routine, the file will be read
sequentially from the record located by the
random read. Note that the sequential read
uses the NEXT. When EOF is reached,
processing will end.
Start and sequential read
Random and sequential read
In this code a random read locates the starting
record. If the locate is successful, then the
NEXT record is read and processed.
MOVE START-PT TO MID.
MOVE "YES" TO MSTR-FOUND.
READ MASTER-FILE
INVALID KEY
MOVE "NO " TO MSTR-FOUND
NOT INVALID KEY
MOVE “YES” TO MSTR-FOUND
END-READ.
IF MSTR-FOUND = "YES”
READ MASTER-FILE NEXT
AT END
MOVE "YES" TO EOF-MSTR.
To mix random and sequential read
statements, dynamic access must be
specified.
In this code the start verb locates the starting
record but does not read it. The first time the
READ is executed the record that was located
is read and processed.
MOVE START-PT TO MID.
MOVE “YES” TO MSTR-FOUND.
START MASTER-FILE
KEY >= MID
INVALID KEY
MOVE “NO “ TO MSTR-FOUND
NOT INVALID KEY
MOVE “YES” TO MSTR-FOUND
END-START
IF MSTR-FOUND = “YES”
READ MASTER-FILE
AT END
MOVE “YES’ TO EOF-MSTR.
Alternate key
SELECT MASTER-FILE
ASSIGN TO "C:\PCOBWIN\VSAM\VSAMALT.DAT"
ORGANIZATION IS INDEXED
ACCESS IS DYNAMIC
RECORD KEY IS MID
ALTERNATE RECORD KEY IS MITEM-NAME WITH DUPLICATES.
Sequential read using alternate key:
Random read using alternate key:
(Assumes that the start point and alternate key path
has been established).
MOVE RETR-NAME TO MITEM-NAME.
READ MASTER-FILE
KEY IS MITEM-NAME
INVALID KEY
PERFORM B-410-INVALID
NOT INVALID KEY
PERFORM B-400-PROCESS.
READ MASTER-FILE NEXT
AT END
MOVE "YES" TO EOF-IND.
The sequential read is assuming that
the path has been established by a
previous random read.
SELECT MASTER-FILE
ASSIGN TO "C:\PCOBWIN\VSAM\VSAM1.DAT"
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS MID
FILE STATUS IS WS-FILE-STATUS.
File status
01 WS-FILE-STATUS
PIC XX
VALUE SPACES.
MOVE RETR-ID TO MID.
READ MASTER-FILE
INVALID KEY
PERFORM B-310-INVALID.
IF WS-FILE-STATUS = "00"
PERFORM B-300-PROCESS.
Because of the file status clause in the
select, the file status is retrieved every
time this record is used. A file status of
00 means that the processing was
successful. Charts that give meaning to
the specific numbers are available in
COBOL manuals.
B-310-INVALID.
MOVE RETR-ID TO PID.
IF WS-FILE-STATUS = "23"
MOVE "RECORD MISSING" TO PMSG
ELSE
MOVE "OTHER PROBLEM" TO PMSG.
File status
01
WS-FILE-STATUS
PIC XX
VALUE SPACES.
SELECT MASTER-FILE
ASSIGN TO "C:\PCOBWIN\VSAM\VSAM1.DAT"
ORGANIZATION IS INDEXED
ACCESS IS RANDOM
RECORD KEY IS MID
FILE STATUS IS WS-FILE-STATUS.
PROCEDURE DIVISION.
DECLARATIVES.
ERROR-HANDLING SECTION.
USE AFTER ERROR PROCEDURE
ON MASTER-FILE.
ERROR-CHECK.
IF WS-FILE-STATUS = "23"
MOVE RETR-ID TO PID
MOVE "RECORD MISSING " TO PMSG
WRITE PRINTZ
AFTER ADVANCING 1 LINES
END-IF.
END DECLARATIVES.
MAIN-PROGRAM SECTION.
MAINLINE.
PERFORM A-100-INITIALIZE.
PERFORM B-100-PROCESS.
PERFORM C-100-TERMINATE.
STOP RUN.
B-200-LOOP.
MOVE SPACES TO PRINTZ.
MOVE RETR-ID TO MID.
READ MASTER-FILE.
IF WS-FILE-STATUS = "00"
PERFORM B-300-PROCESS
END-IF.
The declaratives part of the
program is where you can set up
error handling procedures that
can be applied to a file. Note
that the read has no clause
associated with it. If the read is
unsuccessful control switches to
the the error-handling section
and appropriate processing is
done.