VSAM KSDS and COBOL
Department of Computer Science
Northern Illinois University
August 2005
Some of the illustrations are from VSAM: Access Method Services
and Programming Techniques by James Martin
Processing a KSDS
• KSDS can be processed 3 ways
– Sequentially
• Records accessed in key sequence
– Randomly
• Records accessed via a specified key value
– Dynamically
• Records accessed both sequentially and
randomly
2
Sequentially Processing
a KSDS
• Access records in ascending order on
the file’s key field
• Usually begin with the first record and
process to the end
3
File-Control for
Sequential KSDS
File-Control.
SELECT file-name
ASSIGN to ddname
ORGANIZATION is INDEXED
ACCESS MODE is SEQUENTIAL
RECORD KEY is data-name-1
FILE STATUS is data-name-2.
4
File-Control for
Sequential KSDS
• File-Control.
SELECT file-name
where file-name is the name used for the
file throughout the program
5
File-Control for
Sequential KSDS
• File-Control.
ASSIGN to ddname
where ddname is the ddname in the JCL
used to refer to the KSDS file
6
File-Control for
Sequential KSDS
• File-Control.
ORGANIZATION is INDEXED
where INDEXED specifies that this file is
a KSDS
7
File-Control for
Sequential KSDS
• File-Control.
ACCESS MODE is SEQUENTIAL
where SEQUENTIAL specifies that the
processing of the KSDS will be in
order on the key field of the file
8
File-Control for
Sequential KSDS
• File-Control.
RECORD KEY is data-name-1
where data-name-1 is the file’s key field
and the records are going to be
accessed ascending on this field
data-name-1 must appear in the file’s record
description in the FILE SECTION
9
File-Control for
Sequential KSDS
• File-Control.
FILE STATUS is data-name-2
where data-name-2 is a filed you specify
in which VSAM provides information
about each I/O operation
VSAM places a return code in data-name-2
for the application program to determine
the result of the I/O operation
10
Common File Status for KSDS
Code
Meaning
00
Successful completion
10
21
22
23
End of file reached
Sequence error
Duplicate key
Record not found
24
No more space
11
FD Statement in KSDS
FD KSDS-file
LABEL RECORDS ARE [OMITTED
or STANDARD].
Treated as a comment but is required
12
Procedure Division in
KSDS Sequential Processing
•
•
•
•
•
•
•
OPEN statement
START statement
READ statement
WRITE statement
REWRITE statement
DELETE statement
CLOSE statement
13
KSDS OPEN Statement
• OPEN statement (sequentially)
• Must open all files
– Loading sequentially
• OPEN OUTPUT ksds-file.
– Retrieving sequentially
• OPEN INPUT ksds-file.
14
KSDS START Statement
• START statement
– Used to start sequential processing with a
record other than the first record in the file
– Use with a file that is opened as input or
dynamically (I-O) and processing
sequentially
– To use, place a value in the record key
area
15
KSDS START Statement
• START statement
START vsam-file
[KEY IS {EQUAL TO
=
GREATER THAN
>
NOT LESS THAN
NOT <
GREATER THAN OR EQUAL TO
>= }
record-key]
[INVALID KEY imperative-1]
[NOT INVALID KEY imperative-2]
[END-START]
16
KSDS READ Statement
• READ statement (sequential)
– To retrieve records in key sequence, open
KSDS for either
• INPUT or
• I-O
17
KSDS READ Statement
• READ statement (sequential)
READ file-name RECORD [INTO area]
[AT END imperative-1]
NOT AT END imperative-2]
[END-READ]
18
KSDS READ Statement
• READ statement (sequential)
READ file-name [NEXT]
Specify NEXT on the READ statement to retrieve
records sequentially when file is opened for I-O
Omit NEXT when file is opened for I-O and the
records will be retrieved randomly based on the value
in the RECORD KEY field
19
KSDS READ Statement
• READ statement (sequential)
– The key using dynamic access is knowing
how to switch from sequential to random
access.
– The position for sequential retrieval is
changed only by a START or a random
READ statement.
20
KSDS READ Statement
• READ statement (sequential)
– A random READ statement can be used to
retrieve a specific record and then can be
followed by a sequential READ statement
(using the NEXT option)
21
KSDS WRITE Statement
• WRITE statement (sequential)
– KSDS must be opened for
• OUTPUT for file creation (loading of data)
• I-O for file additions
– A value must be placed into the primary
key field prior to the write
22
KSDS WRITE Statement
• WRITE statement (sequential)
WRITE record-name [FROM area]
[INVALID-KEY imperative-1]
[NOT INVALID-KEY imperative-2]
[END-WRITE]
23
KSDS WRITE Statement
• WRITE statement (sequential)
– INVALID-KEY imperative-1 is executed when
• the value stored in the primary key field prior to
issuing the WRITE is equal to that of a record
already in the file
• an attempt is made to write beyond the
boundaries of the file
• the primary key is not greater than the primary
key of the previous record AND the file is
opened for OUTPUT and sequential accessing
is specified
24
KSDS REWRITE Statement
• REWRITE statement (sequential)
– the KSDS must be opened for I-O
– the record to be rewritten needs to be the
last record read from the file
• must read the record prior to rewriting it
25
KSDS REWRITE Statement
• REWRITE statement (sequential)
REWRITE record-name [FROM area]
[INVALID KEY imperative-1]
[NOT INVALID KEY imperative-2]
[END-REWRITE]
26
KSDS REWRITE Statement
• REWRITE statement (sequential)
– [INVALID KEY imperative-1] is executed when
• the record to be changed does not exist in the
file
• sequential access is specified and the value
placed in the primary key doesn’t equal the
primary key fo the previously read record
27
KSDS DELETE Statement
• DELETE statement (sequential)
– KSDS opened as I-O
– delete the record read in the last READ
statement
– the space in KSDS is immediately
available for reuse
28
KSDS DELETE Statement
• DELETE statement (sequential)
DELETE file-record RECORD
[INVALID-KEY imperative-1]
[NOT INVALID-KEY imperative-2]
[END-DELETE]
29
KSDS DELETE Statement
• DELETE statement (sequential)
– [INVALID-KEY imperative-1] is executed when
• an attempt to delete a record that does not
exist is made
30
KSDS CLOSE Statement
• CLOSE statement (sequential)
– list the KSDS that is to be closed
31
KSDS Load Program
in COBOL
• Go over handout
“COBOL JCL
& Source Review for Loading KSDS”
32
KSDS Random Processing
• All I/O operations depend upon the
record key
• Before READ a value must be in the
record key
• Before WRITE a value must be in the
record key
33
File-Control for
Random KSDS
File-Control.
SELECT file-name
ASSIGN to ddname
ORGANIZATION is INDEXED
ACCESS MODE is RANDOM
RECORD KEY is data-name-1
FILE STATUS is data-name-2.
34
File-Control for
Random KSDS
File-Control.
ACCESS MODE is RANDOM
The only difference in the SELECT statement
for random processing is the word
RANDOM access
35
Procedure Division in
KSDS Random Processing
•
•
•
•
•
•
OPEN statement
READ statement
WRITE statement
REWRITE statement
DELETE statement
CLOSE statement
36
KSDS OPEN Statement
• OPEN statement (random)
• Must open all files
– Retrieving randomly
• OPEN INPUT ksds-file.
– Writing randomly
• OPEN OUTPUT ksds-file.
– Reading, rewriting and deleting randomly
• OPEN I-O ksds-file.
37
KSDS READ Statement
• READ statement (random)
– To retrieve records based upon value in the
record key field, open KSDS for either
• INPUT or
• I-O
38
KSDS READ Statement
• READ statement (random)
– To retrieve records based upon value in the
record key field, open KSDS for either
• INPUT or
• I-O
39
KSDS READ Statement
• READ statement (random)
READ file-name RECORD [INTO area]
[KEY IS data-name-1]
[INVALID KEY imperative-1]
NOT INVALID KEY imperative-2]
[END-READ]
40
KSDS READ Statement
• READ statement (random)
[KEY IS data-name-1]
The key value of the record that is to be retrieved
from the KSDS must be placed in data-name-1 prior
to issuing the READ statement.
41
KSDS READ Statement
• READ statement (random)
– when invoked comparison is made
• between the value of the field specified in the
RECORD KEY clause of the SELECT
statement (known as “key of reference”) and
• the key values of the KSDS records
– search is done via the index
– appropriate control interval is read into
memory and sequentially searched
42
KSDS WRITE Statement
• WRITE statement (random)
WRITE record-name [FROM area]
[INVALID-KEY imperative-1]
[NOT INVALID-KEY imperative-2]
[END-WRITE]
43
KSDS WRITE Statement
• WRITE statement (random)
– used to add records to a file
– KSDS uses the RECORD KEY value to write the
record in its proper physical location
44
KSDS REWRITE statement
• REWRITE statement (random)
REWRITE record-name [FROM area]
[INVALID KEY imperative-1]
[NOT INVALID KEY imperative-2]
[END-REWRITE]
45
KSDS REWRITE statement
• REWRITE statement (random)
– used to update a record in its original physical
location
– KSDS uses the RECORD KEY value to rewrite the
record in its proper physical location
46
KSDS DELETE Statement
• DELETE statement (random)
DELETE file-record RECORD
[INVALID-KEY imperative-1]
[NOT INVALID-KEY imperative-2]
[END-DELETE]
47
KSDS DELETE Statement
• DELETE statement (random)
– used to delete a record from its physical location
– KSDS uses the RECORD KEY value to find the
record to delete
48
KSDS CLOSE Statement
• CLOSE statement (random)
– list the KSDS that is to be closed
49
KSDS Dynamic Processing
• Processing can be a mix of sequential
and random
• All the statements remain the same
except the SELECT and the sequential
READ
50
KSDS Dynamic Processing
• Using dynamic processing effectively is
knowing how to switch from sequential
to random access
– position for sequential retrieval by a
• START or
• random READ
– issue READ using NEXT for sequential
processing
51
KSDS Dynamic Processing
• Note:
– During dynamic processing issuing a
WRITE, REWRITE, or DELETE statement
does not change file position
– Use START or random READ to change
file position
52
File-Control for
Dynamic KSDS
File-Control.
SELECT file-name
ASSIGN to ddname
ORGANIZATION is INDEXED
ACCESS MODE is DYNAMIC
RECORD KEY is data-name-1
FILE STATUS is data-name-2
53
KSDS READ Statement
• READ statement (dynamic)
READ file-name [NEXT] RECORD [INTO area]
[KEY IS data-name-1]
[INVALID KEY imperative-1]
NOT INVALID KEY imperative-2]
[END-READ]
54
KSDS READ Statement
• READ statement (dynamic)
– NEXT is used in dynamic processing of
KSDS to retrieve records sequentially on
the key
– if NEXT is omitted the records are retrieved
randomly based on the value in the
RECORD KEY field
55