IMS DB
Objectives
• To create awareness about the IMS DB
technology and how it is used to
perform data base operations.
• Target audience :- people who are
relatively new to the IMS DB
Technology.
Prerequisites
•
•
Knowledge of COBOL
Basic knowledge of data base management concepts
Course Outline
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
An Introduction to DL/I Data Bases
DL/I Programs and Control Blocks
COBOL Basics for Processing a DL/I Data Base
Segment Search Arguments : How to use them
Data retrieval from an IMS Data Base
Adding and Updating Data to a Data Base
Secondary Indexing
Logical Data Bases
Recovery and Restart
DL/I Data Base Organizations
Advanced DL/I features
References
•
IMS for the COBOL Programmer
Part 1: Data base processing with IMS/VS and DL/I
DOS/VS
By Steve Eckols
•
IBM Redbooks : IMS Primer
By Rick Long, Mark Harrington, Robert Hain, Geoff
Nicholls
•
MVS Quick Ref Ver. 5.5
Module 1
An Introduction to DL/I Data
Bases
Hierarchical Structures
Why a Data Base Management System
Basic DL/I Terminology
Basic DL/I Data Base Processing
Hierarchical Structures
•
•
In a DL/I data base, data elements are organized in a hierarchical structure.
Some data elements are dependent on others.
Fig 1.1 A hierarchical structure
DL/I supports hierarchies that are difficult to implement with standard files.
Why a data base management system?
01
VENDOR-RECORD.
05 VR-VENDOR-CODE
PIC X(3).
05 VR-VENDOR-NAME
PIC X(30).
05 VR-VENDOR-ADDRESS
PIC X(30).
05 VR-VENDOR-CITY
PIC X(17).
05 VR-VENDOR-STATE
PIC XX.
05 VR-VENDOR-ZIP-CODE
PIC X(9).
05 VR-VENDOR-TELEPHONE
PIC X(10).
05 VR-VENDOR-CONTACT
PIC X(30).
Fig 1.2.a Record layout for the VENDORS data set
01 INVENTORY-RECORD.
05 IR-ITEM-KEY.
10 IR-VENDOR-CODE
PIC X(3).
10 IR-NUMBER
PIC X(5).
05 IR-DESCRIPTION
PIC X(35).
05 IR-UNIT-PRICE
PIC S9(5)V99 COMP-3.
05 IR-AVG-UNIT-COST
PIC S9(5)V99 COMP-3.
05 IR-LOCATION-QUANTITY-DATA OCCURS 20 TIMES.
10 IR-LOCATION
PIC X(3).
10 IR-QUANTITY-ON-HAND
PIC S9(7) COMP-3.
10 IR-REORDER-POINT
PIC S9(7) COMP-3.
10 IR-QUANTITY-ON-ORDER
PIC S9(7) COMP-3.
10 IR-LAST-REORDER-DATE
PIC X(6).
Fig 1.2.b Record layout for the Inventory Master data set
Fig 1.2 Record layouts that illustrate a hierarchical structure
Basic DL/I Terminology
•
Segment
– A grouping of data
– The unit of data that DL/I transfers to and from your program in an I/O operation.
– Consists of one or more fields
Fig 1.3 The ADDRESS segment with six fields
ADDRESS
Segment Type
House
Number
Street
Name
City
State
Country
Zip Code
A category of data
There can be a maximum of 255 segment types and 15 levels in one data base
Segment Occurrence
One specific segment of a particular type containing user data
Note: Within a data base there is only one of each segment type- it’s part of the data base’s definitionbut there can be an unlimited number of occurrences of each segment type.
 The word ‘segment’ is used to mean either ‘segment type’ or ‘segment occurrence’ and usually
the meaning is clear from the context
Basic DL/I Terminology (contd.)
*
01 INVENTORY-VENDOR-SEGMENT.
05 IVS-VENDOR-CODE
05 IVS-VENDOR-NAME
05 IVS-VENDOR-ADDRESS PIC X(30).
05 IVS-VENDOR-CITY
05 IVS-VENDOR-STATE
05 IVS-VENDOR-ZIP-CODE PIC X(9).
05 IVS-VENDOR-TELEPHONE
PIC X(3).
PIC X(30).
PIC X (17).
PIC XX.
PIC X(10).
*
01 INVENTORY-ITEM-SEGMENT.
05 IIS-NUMBER
05 IIS-DESCRIPTION
05 IIS-UNIT-PRICE
05 IIS-AVG-UNIT-COST
PIC S9(5)V99
PIC X(5).
PIC X(35).
PIC S9(5)V99 COMP-3.
COMP-3.
*
01 INVENTORY-STOCK-LOC-SEGMENT.
05 ISLS-LOCATION
PIC X(3).
05 ISLS-QUANTITY-ON-HAND
PIC S9(7) COMP-3.
05 ISLS-REORDER-POINT
PIC S9(7) COMP-3.
05 ISLS-QUANTITY-ON-ORDER
PIC S9(7) COMP-3.
*
Vendor
Fig 1.5 Segment layouts for the Inventory data base
Item
Stock Location
Fig 1.4 The hierarchical structure of the Inventory
data base with three segment types
Basic DL/I Terminology (contd.)
•
Root Segment
– The segment type at the top of a hierarchy
•
Data base record
– Each occurrence of the root segment plus all the
segment occurrences that are subordinate to it
make up one data base record. Every data base
Vendor
2
Vendorone
1
record has
and only one root
segment,
Item 2
although it may have
any numberItemof1 subordinate
Data base Record
2
Item 1
segment occurrences Loc 2
Loc 2
Data base
Record 1
Loc 1
Loc 1
Fig 1.6
LocTwo
5 data base records from the Inventory data base
Loc 4
Loc 3
Loc 2
Loc 1
Basic DL/I Terminology (contd.)
•
Dependent Segment
– A segment other than the root segment in a data
base record
– Accessible only through one or more “parent”
segments
•
Parent Segment
– A segment that has one or more dependent
segments
•
Child Segment
– Every dependent segment in a hierarchy
•
Twin Segment
– Two or more segment occurrences of the same
Basic DL/I Terminology (contd.)
•
Key or Sequence Field
– The field DLI uses to maintain segments in
ascending sequence
– Only a single field within a segment
– Segments need not necessarily require a key field
– If in a root segment, key field uniquely identifies
the record
•
Additional Search fields
– Used to search through the DB for particular
values
•
Basic DL/I Terminology (contd.)
Logical data bases
– Additional relationships within one physical data base
Customer
Ship-to
Buyer
Vendor
Item
Receivable
Stock Location
Payment
Fig 1.7 A logical relationship can connect two data bases
Adjustment
Line Item
– In Fig 1.7, the line item segment is the logical child segment (or just logical child) of the item
segment.
– Likewise, the item segment is the logical parent segment (or just logical parent) of the line item
segment
•
Basic DL/I Data Base Processing
Sequential Processing
– Top –> Down, Left -> Right
– Position
• At any point, a program has a position in the data base.
• Position reflects not only on retrieved segments, but on new segments inserted as well
Vendor 2
Vendor 1
Item 1
Item 2
Data base Record 2
Item 1
Loc 2
Loc 2
Data base
Record 1
Loc 1
Loc 5
Loc 4
Loc 3
Loc 2
Loc 1
Fig 1.8 Sequential processing
Loc 1
•
Basic DL/I Data Base Processing
Random (Direct) Processing
(contd.)
– Key (sequence) field required
– Concatenated Key
• Completely identifies the path from the root segment to the segment you want to
retrieve.
Vendor 2
Vendor 1
Item 1
Item 2
Data base Record 2
Item 1
Loc 2
Loc 1
Data base
Record 1
Loc 5
Loc 4
Loc 3
Loc 2
Loc 1
Concatenated Key:
Vendor 2
Item 1
Location 1
Fig 1.9 Random Processing
Loc 2
Loc 1
Module 2
DL/I Programs and Control Blocks
The IMS Software Environment
How DL/I relates to your application programs
Control Blocks
DBDGEN
PSBGEN
IMS Processing Options
ACB & ACBGEN
Running an application program under DL/I
The IMS Software Environment
Application
Programs
IMS Control
Blocks
DL/I
OS
Data Base
Fig 2.1 The IMS Software Environment
IMS DC
Remote
Terminal
How DL/I relates to
your application programs
Standard File Processing
DL/I Data Base Processing
Application
Program
Application
Program
DL/I
Operating System
Access Method
Operating System
Access Method
(eg. VSAM)
(eg. VSAM)
File
Data Set
Data Base
Data Set
Fig 2.2 Standard file processing compared to DL/I data base processing
How DL/I relates
to your application programs (contd.)
•
Standard file processing
– Standard COBOL statements (like READ / WRITE) invoke the
appropriate access method (like VSAM)
– Format of the record as processed by the program should be the same
as the format of the record in the file
•
DL/I data base processing
–
–
–
–
DLI - Interface between application program and the access method
CALL statement to invoke DL/I
Parameters passed by the CALL tell DL/I what operation to perform
DL/I invokes a standard access method- usually VSAM- to store data
base data on disk
– Format of records in a data base data set need not match the layouts
of the segments that make up the data base
– The way the program sees the data base is different from the way the
access method sees it.
•
•
•
Control Blocks
Physical structure of a DL/I data base isn’t specified in an application program
DL/I uses a set of control blocks(DBDs and PSBs) to define a data base’s structure
Data Base Descriptor (DBD)
– Describes the complete structure of a data base
– A unique DBD for each DL/I data base
•
Program Specification Block (PSB)
– Application program’s view of the Database
– PSB Specifies
• Data bases (one or more) a program can access,
• Data elements a program can “see” in those data bases
• The processing a program can do with the data elements
– Application programs that have similar data base
processing requirements can share a PSB
•
•
Data Base Administrator (DBA) has to create DL/I control blocks
DBDGEN and PSBGEN Control Statements
STMT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
72
73
74
75
76
77
78
79
80
162
211
325
326
SAMPLE DBDGEN (Explained in next
slide)
SOURCE STATEMENT
PRINT
NOGEN
DBD
NAME=INDBD,ACCESS=HIDAM
DATASET DD1=IN,DEVICE=3380
**/
3380 DISK STORAGE
*
SEGM
NAME=INVENSEG, PARENT=0,POINTER=TB,BYTES=131
LCHILD NAME=(INPXPNTR,INPXDBD),POINTER=INDX
FIELD
NAME=(INVENCOD,SEQ),BYTES=3,START=1,TYPE=C
FIELD
NAME=INVENNAM,BYTES=30,START=4,TYPE=C
FIELD
NAME=INVENADR,BYTES=30,START=34,TYPE=C
FIELD
NAME=INVENCIT,BYTES=17,START=64,TYPE=C
FIELD
NAME=INVENSTA,BYTES=2,START=81,TYPE=C
FIELD
NAME=INVENZIP,BYTES=9,START=83,TYPE=C
FIELD
NAME=INVENTEL,BYTES=10,START=92,TYPE=C
FIELD
NAME=INVENCON,BYTES=30,START=102,TYPE=C
*
SEGM
NAME=INITMSEG,PARENT=INVENSEG,BYTES=48
FIELD
NAME=(INITMNUM,SEQ),BYTES=5,START=1,TYPE=C
FIELD
NAME=INITMDES,BYTES=35,START=6,TYPE=C
FIELD
NAME=INITMPRC,BYTES=4,START=41,TYPE=P
FIELD
NAME=INITMCST,BYTES=4,START=45,TYPE=P
*
SEGM
NAME=INLOCSEG, PARENT=INITMSEG,BYTES=21
FIELD
NAME=(INLOCLOC,SEQ),BYTES=3,START=1,TYPE=C
FIELD
NAME=INLOCONH,BYTES=4,START=4,TYPE=P
FIELD
NAME=INLOCROP,BYTES=4,START=8,TYPE=P
FIELD
NAME=INLOCONO,BYTES=4,START=12,TYPE=P
FIELD
NAME=INLOCDAT,BYTES=6,START=16,TYPE=C
*
DBDGEN
**/**************************************************************************
**/
RECOMMENDED VSAM DEFINE CLUSTER PARAMETERS
**/**************************************************************************
**/*
*NOTE2
**/* DEFINE CLUSTER (NAME(IN) NONINDEXED **/*
RECORDSIZE (2041,2041) **/*
COUNTERINTERVALSIZE (2048))
**/* *NOTE2 - SHOULD SPECIFY DSNNAME FOR DD IN
**/**************************************************************************
**/***********SEQUENCE FIELD*************
**/***********SEQUENCE FIELD*************
FINISH
END
Fig 2.3 Assembler source listing for the Inventory data base DBDGEN
SAMPLE DBDGEN (contd.)
•
Explanation of Fig 2.3
– First macro – DBD – identifies the data base and specifies the
DL/I access method
– Second macro – DATASET- identifies the file that would contain
the data base
– Symbolic name (IN) identifies the data set in the JCL at
execution time
– Segment types are defined using the SEGM macro
– Segment hierarchical relationships are specified by the PARENT
parameter on a SEGM macro
• PARENT= 0 or absence of PARENT parameter specifies root segment
– POINTER parameter and LCHILD macro are needed for HIDAM
Databases
– Only search fields need be specified in the DB
DBDGEN
(contd.)
– FIELD macro defines a field in the DB
•
•
•
•
START
 position of field within segment
NAME  name of the field
LENGTH  length of the field
TYPE
 data type of the field
FIELD Macro TYPE Codes
Data Type
C
Character
P
Packed decimal
Z
Zoned decimal
X
Hexadecimal
H
Half word Binary
F
Full word Binary
Fig 2.4 FIELD macro TYPE parameter codes
SEQ parameter specifies a sequence field
segment occurrences are added in sequence by values in these fields
SAMPLE PSBGEN
STMT SOURCE STATEMENT
1
PRINT
NOGEN
2
PCB
TYPE=DB,DBDNAME=INDBD,PROCOPT=LS
3
SENSEG
NAME=INVENSEG
4
SENSEG
NAME=INITMSEG,PARENT=INVENSEG
5
SENSEG
NAME=INLOCSEG,PARENT=INITMSEG
6
PSBGEN
PSBNAME=INLOAD,LANG=COBOL
87 END
Fig 2.5 Assembler source listing for the Inventory data base load program’s PSBGEN
•
Explanation of Fig 2.5
– PCB (Program Communication Block) refers to one data
base.
– One PCB macro for each database accessed
– Segment Level Sensitivity
• A program’s access to parts of the data base identified at the segment level
• Within sensitive segments, the program has access to all fields
– Field level sensitivity
• When the program accesses that segment, only sensitive fields are presented
PSBGEN (contd.)
– DBDNAME parameter on the PCB macro specifies the name of
the DBD
– KEYLEN parameter specifies the length of the longest
concatenated key the program can process in the data base
– PROCOPT parameter specifies the program’s processing options
– For each PCB macro, subordinate SENSEG macros identify the
sensitive segments in the data base
– Names specified in the SENSEG macros must be segment names
from the DBDGEN for the data base named in the DBDNAME
parameter of the PCB macro
– PSBGEN macro
• Indicates that there are no more statements in the PSBGEN job
• PSBNAME parameter specifies the name to be given to the output PSB module
• LANG parameter specifies the language in which the related application program will be
written.
IMS Processing Options
•
•
Indicates to IMS the type of access allowed for a sensitive segment (SENSEG)
Commonly used Processing Options
–
–
–
–
–
–
–
•
PROCOPT=G means only read-only access
PROCOPT=R means read/replace access
PROCOPT=I means insert access allowed
PROCOPT=D means Read/Delete access
PROCOPT=A means all the above options present
For GSAM DBs PROCOPT=LS for output and GS (Get Sequential) for input
PROCOPT=L allows a 'load' into the DB. If VSAM DB, it should be empty prior to the
load
The PROCOPT given for a Sensitive segment would override the one given for
the DB
– Example : PCB TYPE=DB,NAME=LDB42F,PROCOPT=G,
KEYLEN=200 SENSEG NAME=SEGL4201,
PARENT=0,PROCOPT=A
– WARNING : Indiscriminate use of PROCOPTS can lead to inexplicable results !
ACB & ACBGEN
•
•
•
•
•
•
•
ACB(Application Control Blocks) : It is created by merging and expanding PSB’s and
DBD’s into an IMS internal format when an application program is scheduled for
execution.
ACBGEN : The process of building ACB is called Block Building and is done by
means of ACBGEN.
IMS can build ACB’s either dynamically or it can prebuild them using ACB
maintenance utility.
ACB’s cannot be prebuilt for GSAM DBD’s.
ACB’s can be prebuild for PSB’s that reference GSAM databases.
ACB’s save instruction, execution and direct-access wait time and improves
performance in application scheduling.
ACB’s are maintained in IMS.ACBLIB library.
Running an application program under
DL/I
• Batch program does not access IMS directly
• JCL invokes the DL/I ‘batch initialization module’ DFSRRC00 which loads
the application program and the required DL/I modules
• The program and DL/I modules execute together
• Sample JCL :
//JOBNAME JOB (ACCT),'PGMR NAME',
//
CLASS=J,
//
MSGCLASS=Z,
//
NOTIFY=&SYSUID
//JOBLIB DD DSN=YOUR.PROGRAM.LOAD.LIBRARY,
//
DISP=SHR
//
DD DSN=YOUR.SYSTEM.RESLIB.LIBRARY,
//
DISP=SHR
//PROC EXEC PROCNAME, SYMBOLIC PARAMETERS
//*********************************************************
//PROCNAME PROC
//********************************************************
//* THIS PROC LOADS AN IMS VSAM DATABASE
//* A PROGRAM 'LOAD' IS USED FOR THIS PURPOSE
//* THE PSB USED FOR LOADING IS LOADPSB
//********************************************************
//LOAD
EXEC PGM=DFSRRC00,
//
PARM='DLI,LOAD,LOADPSB'
SAMPLE JCL (Contd.)
//DFSRESLB DD DSN=YOUR.DFRESLIB.LIBRARY,
//
DISP=SHR
//IMS
DD DSN=YOUR.DBD.LIBRARY,
//
DISP=SHR
//
DD DSN=YOUR.PSB.LIBRARY,
//
DISP=SHR
//IMSLOGR
DD DSN=YOUR.IMSRLOG.DATASET,
//
DISP=SHR
//IEFRDER
DD DSN=YOUR.IEFRDER.DATASET,
//
DISP=OLD
//* DD NAMES ARE AS SPECIFIED IN THE DATABASE
//DATA
DD DSN=VSAMDB.DATA.PART,DISP=SHR
//INDEX
DD DSN=VSAMDB.INDEX.PART,DISP=SHR
//INPUT
DD DSN=FILE.USED.FOR.LOADING,
//
DISP=SHR
//DFSVSAMP DD DSN=IMSVS.PROCLIB(DFSVSAMP),
//
DISP=SHR
//CPXMOPTS DD DSN=PARMLIB.LIBRARY(LOAD),
//
DISP=SHR
//CPXMRPTS DD SYSOUT=*
//SYSOUT
DD SYSOUT=*
//SYSPRINT DD SYSOUT=*
//SYSUDUMP DD SYSOUT=*
//IMSERR
DD SYSOUT=*
//IMSPRINT DD SYSOUT=*
Module 3
COBOL Basics for Processing a
DL/I Data Base
The ENTRY and GO BACK Statements
The DL/I Call
The PCB Mask
ENTRY and
GO BACK Statements
ENTRY ‘DLITCBL’
USING
PCB-name1
[PCB-name2...]
Fig 3.1 Format of the DL/I ENTRY Statement
•
•
•
•
•
•
Application program is invoked under the control of the batch initialization module
DLITCBL => ‘DL/I to COBOL’ is the entry point to the program
DL/I supplies the address of each PCB defined in the program’s PSB
PCBs must be defined in the Linkage Section
Linkage Section definition of a PCB is called a ‘PCB Mask’
Addressability to PCBs established by listing the PCB Masks on the ENTRY
statement
•
PCB masks should be listed on the ENTRY statement in the same sequence as they appear in
your program’s PSBGEN
GO BACK Statement
•
–
–
When a program ends, it passes control back to the DL/I
DL/I reallocates resources and closes the data base data sets
The DL/I Call
•
•
CALL statements are used to request DL/I services
Parameters you code on the CALL statement specify, among other things, the
operation you want DL/I to perform
CALL ‘CBLTDLI’ USING
DLI-function
PCB-mask
segment-io-area
[segment-search-argument(s)]
Fig 3.2 Format of the DL/I call
•
•
CBLTDLI => ‘COBOL to DL/I’, is an interface module that is link edited with your
program’s object module
PLITDLI, ASMTDLI are other options
The DL/I Call (contd.)
• The DL/I Function
– First parameter coded on any DL/I call
– Four character working storage field containing the function code
01 DLI-FUNCTIONS.
05 DLI-GU
05 DLI-GHU
05 DLI-GN
05 DLI-GHN
05 DLI-GNP
05 DLI-GHNP
05 DLI-ISRT
05 DLI-DLET
05 DLI-REPL
05 DLI-CHKP
05 DLI-XRST
05 DLI-PCB
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
X(4)
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
VALUE
‘GU ’.
‘GHU ’.
‘GN ’.
‘GHN ’.
‘GNP ’.
‘GHNP’.
‘ISRT’.
‘DLET’.
‘REPL’.
‘CHKP’.
‘XRST’.
‘PCB ’.
The DL/I Call (contd.)
– Get functions
• First six 05-level items in Fig 3.3
• Used to retrieve segments from a DL/I data base
• GU  ‘get unique’ function causes DL/I to retrieve a specific segment
occurrence based on field values that you specify
• GN  ‘get next’ function used to retrieve segment occurrences in
sequence
• GNP  ‘get next within parent’ function lets you retrieve segment
occurrences in sequence, but only subordinate to an established parent
segment
• The three get function codes that contain an H are ‘get hold functions’
and are used to specify an intent to update a segment after you retrieve it
• GHU or the ‘get hold unique’ function corresponds to GU
• GHN or the ‘get hold next’ function corresponds to GN
• GHNP or the ‘get hold next within parent’ function corresponds to GNP
– Update functions
The DL/I Call (contd.)
– Other functions
• Functions CHKP (the ‘checkpoint’ function) and XRST (the ‘restart’
function) are used in programs to take advantage of IMS’s recovery and
restart features
• Function PCB is used in CICS programs
• Function SYNC is used for releasing resources that IMS has locked for the
program (applicable only in a BMP)
• Function INIT allows an application to receive status codes
regarding deadlock and data availability (from DB PCBs)
The DL/I Call (contd.)
•
PCB mask
– Second parameter on the DL/I call
– The name of the PCB mask defined in the
program’s Linkage Section
– ENTRY statement establishes a correspondence
between PCB masks in the Linkage Section and
the PCBs within the program’s PSB
– After each DL/I call, DL/I stores a status code in
the PCB mask, which the programmer can use to
determine whether the call succeeded or failed
•
Segment I/O Area
– Third parameter on the DL/I call
The DL/I Call (contd.)
•
Segment search argument
– Optional parameter on the DL/I call
– Identifies the segment occurrence you wish to
access
– Multiple SSAs on a single DL/I call
– Two kinds of SSAs– unqualified and qualified
– An unqualified SSA
• Supplies the name of the next segment type that you want to operate on
• If you issue a GN call with an unqualified SSA, DL/I will return the next
occurrence of the segment type you specify
– A qualified SSA
• Combines a segment name with additional information that specifies the
The PCB Mask
•
•
For each data base your program accesses, DL/I maintains an area of storage called
the program communication block (PCB)
Masks are defined for those areas of storage in the Linkage Section of your
program
01 INVENTORY-PCB-MASK.
05 IPCB-DBD-NAME
05 IPCB-SEGMENT-LEVEL
05 IPCB-STATUS-CODE
05 IPCB-PROC-OPTIONS
05 FILLER
05 IPCB-SEGMENT-NAME
05 IPCB-KEY-LENGTH
05 IPCB-NUMB-SENS-SEGS
05 IPCB-KEY
Fig 3.4 PCB mask for an Inventory data base
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
X(8).
XX.
XX.
X(4).
S9(5)
X(8).
S9(5)
S9(5)
X(11).
COMP.
COMP.
COMP.
The PCB Mask (contd.)
•
Data base name
– The name of the data base being processed
•
Segment level
– Specifies the current segment level in the data
base
– After a successful call, DL/I stores the level of the
segment just processed in this field
•
Status code
– Contains the DL/I status code
– When DL/I successfully completes the processing
you request in a call, it indicates that to your
program by moving spaces to the status code field
The PCB Mask (contd.)
•
Key length feedback area
– The field DL/I uses to report the length of the
concatenated key of the lowest level segment
processed during the previous call
– Used with the key feedback area
•
Number of sensitive segments
– Contains the number of SENSEG macros
subordinate to the PCB macro for this data base
•
Key feedback area
– Varies in length from one PCB to another
– As long as the longest possible concatenated key
that can be used with the program’s view of the
Module 4
Segment Search Arguments
Types of SSAs
Basic Unqualified SSA
Basic Qualified SSA
Command Codes
The Null Command Code
Path Call
Multiple Qualifications
Types of SSAs
•
•
SSA identifies the segment occurrence you want to access
It can be either
– Qualified
– Unqualified
•
•
An unqualified SSA simply names the type of segment you want to use
A qualified SSA specifies not only the segment type, but also a specific occurrence
of it
– Includes a field value DL/I uses to search for the
segment you request
– Any field to which the program is sensitive to can
be used in an SSA
•
Because of the hierarchical structure DL/I uses, you often have to specify several
levels of SSAs to access a segment at a low level in a data base
Basic Unqualified SSA
01 UNQUALIFIED-SSA.
*
05 UNQUAL-SSA-SEGMENT-NAME
05 FILLER
*
PIC X(8).
PIC X VALUE SPACE.
Fig 4.1 A basic unqualified SSA
•
•
•
•
A basic unqualified SSA is 9 bytes long
The first eight bytes contain the name of the segment you want to process
If the segment name is less than eight characters long, you must pad it on the right with
blanks
The ninth position of a basic unqualified SSA always contains a blank
– The DL/I uses the value in position 9 to decide what
Basic Unqualified SSA (contd.)
– To access a particular segment type, you must
modify the segment name during program
execution, by moving an appropriate eightcharacter segment name to the field UNQUALSSA-SEGMENT-NAME
– For example,
MOVE ‘INVENSEG’ TO UNQUAL-SSA-SEGMENT-NAME
MOVE ‘INITMSEG’ TO UNQUAL-SSA-SEGMENT-NAME
•
Alternatively, you can code the segment name as a literal when you define a
qualified SSA
Basic Qualified SSA
01
*
VENDOR-SSA.
05
05
05
05
FILLER
FILLER
VENDOR-SSA-CODE
FILLER
PIC
PIC
PIC
PIC
X(9) VALUE ‘INVENSEG(’.
X(10) VALUE ‘INVENCOD =’.
X(3).
X
VALUE ‘)’.
*
Fig 4.2 A basic qualified SSA
•
•
•
•
A qualified SSA lets you specify a particular segment occurrence based on a condition
that a field within the segment must meet
The first eight characters of a basic qualified SSA is the eight character segment name
The ninth byte is a left parenthesis
Immediately following the left parenthesis in positions 10 through 17 is an eight
character field name
Basic Qualified SSA (contd.)
•
After the field name, in positions 18 and 19, you code a two-character relational
operator to indicate the kind of checking DL/I should do on the field in the
segment
– The qualified SSA relational operators are shown
below
(  stands for a single blank space)
Equal to
Not equal to
Greater Than
Greater than or Equal to
Less Than
Less than or Equal to
•
EQ
NE
GT
GE
LT
LE
=
<>
>
>=
<
<=
=
>
=>
<
=<
After the relational operator, you code a variable field into which you move the
Command Codes
Fig 4.3 Unqualified SSA format with a single command code
Fig 4.4 Qualified SSA format with a single command code
•
Command are used in SSAs for three purposes
– To extend DL/I functionality
– To simplify programs by reducing the number of DL/I
calls
Command Codes (contd.)
•
•
•
•
•
•
To use command codes, code an asterisk in position 9 of the SSA
Then code your command codes starting from position 10.
When DL/I finds an asterisk in position 9, it knows command codes will follow
From position 10 onwards, DL/I considers all characters to be command codes
until it encounters a space (for an unqualified SSA) or a left parenthesis (for a
qualified SSA)
It is unusual to use more than one command code in a single SSA
A basic unqualified SSA with a single variable command code is shown below
01 UNQUALIFIED-SSA.
*
05 UNQUAL-SSA-SEGMENT-NAME
05 FILLER
05 UNQUAL-SSA-COMMAND-CODE
05 FILLER
*
PIC
PIC
PIC
PIC
X(8).
X
VALUE “*”.
X.
X
VALUE SPACE.
Command Codes (contd.)
Command Code
Meaning
C
Concatenated Key
D
Path Call
F
First Occurrence
L
Last Occurrence
N
Path Call Ignore
P
Set Parentage
Q
Enqueue Segment
U
Maintain position at this level
V
Maintain position at this and all
superior levels
–
Null command code
Fig 4.5 SSA Command Codes
The Null Command Code
•
•
•
•
Value is a hyphen (–)
Although command code position is present, DL/I ignores it
Particularly useful if you would like to use the same SSA with and without
command codes
An SSA with the null command code is shown below
01 UNQUALIFIED-SSA.
*
05 UNQUAL-SSA-SEGMENT-NAME
05 FILLER
05 UNQUAL-SSA-COMMAND-CODE
05 FILLER
*
PIC
PIC
PIC
PIC
X(8).
X
VALUE “*”.
X
VALUE “-”.
X
VALUE SPACE.
Path Call
•
•
A DB call with an SSA that includes the 'D' Command code is a "PATH CALL“ . It’s a
facility where in we can retrieve an entire path of the segment
Consider a sample GU call
CALL 'CBLTDLI' USING
•
•
•
•
DLI-GU
INVEN-PCB-MASK
INVEN-STOCK-LOC-SEG
VENDOR-SSA
ITEM-SSA
STOCK-LOC-SSA
Normally, DL/I operates on the lowest level segment that is specified in an
SSA(STOCK-LOC-SSA in the above E.g.)
In case if we need data from not just from the lowest level but from other levels as
well we normally have to give 3 separate GU calls.This will reduce the efficiency of
the program
Such a call operates on two or more segments rather than just one segment.
If a program has to use "Path call" then "P" should be one of the values specified
in the PROCOPT parameter of the PCB in the programs PSBGEN.
If path call is not explicitly enabled in the PSBGEN job there will be an 'AM' status
code.
•
Multiple
Qualifications
There are two cases in which you would use multiple qualification
– When you want to process a segment based on the
contents of two or more fields within it
– When you want to process a segment based on a
range of possible values for a single field
•
•
•
•
To use multiple qualification, you connect two or more qualification statements (a field
name, a relational operator, and a comparison value) within the parentheses of the
SSA.
To connect them, you use the Boolean operators AND and OR
Either of the two symbols shown in the table below may be used for AND or OR
The independent AND operator is used for special operations with secondary indexes
and will be discussed later
Multiple Qualifications (contd.)
01 VENDOR-SSA.
*
05 FILLER
05 FILLER
05 VENDOR-SSA-LOW-CODE
05 FILLER
05 FILLER
05 VENDOR-SSA-HIGH-CODE
05 FILLER
•
PIC
PIC
PIC
PIC
PIC
PIC
PIC
X(9)
X(10)
X(3).
X
X(10)
X(3).
X
VALUE ‘INVENSEG(’.
VALUE ‘INVENCOD>=’.
VALUE ‘&’.
VALUE ‘INVENCOD<=’.
VALUE ‘)’.
The above SSA, which uses multiple qualifications can be used to retrieve vendor
segments whose vendor codes fall within a certain range
– The first qualification statement specifies that the
vendor code field must be greater than or equal to
a particular value; that is the low end of the range
– The second qualification statement specifies that
Module 5
Retrieving Data from a Data Base
The GU Call
The GN Call
The GNP Call
Status Codes Expected during Sequential Processing
Using Command Codes with Retrieval Calls
Multiple Processing
The GU Call
•
•
Used for random processing
Applications of random processing
– When a relatively small number of updates are
posted to a large data base
– To establish position in a data base for subsequent
sequential retrieval
•
•
You know what data you want to retrieve and you want to get to it directly
Independent of the position established by the previous calls
CALL ‘CBLTDLI’ USING
DLI-GU
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
VENDOR-SSA
ITEM-SSA
STOCK-LOCATION-SSA.
•
•
The
GU
Call
(contd.)
Usually, GU processing is based on sequence (key) fields with unique values
However, for some applications you may find it necessary to either
– Access a segment whose sequence field allows nonunique values
– Access a segment based on a field that is not the
segment’s key field
– In the above cases, DL/I returns the first segment
occurrence with the specified search value
•
Special considerations for GU calls without a full set of qualified SSAs
1. When you use an unqualified SSA in a GU call, DL/I
accesses the first segment occurrence in the data
base that meets the criteria you specify
2. If you issue a GU call without any SSAs, DL/I returns
the first occurrence of the root segment in the data
base
The GU Call (contd.)
•
Status codes you can expect during random processing with GU calls
– Only two status code values need to be
considered– spaces and GE
– Spaces means the call was successful and the
requested segment was returned in your
program’s segment I/O area
– A GE status code indicates that DL/I couldn’t find a
segment that met the criteria you specified in the
call
The GN Call
CALL ‘CBLTDLI’ USING
•
•
•
•
•
•
•
•
DLI-GN
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
STOCK-LOCATION-SSA.
Used for basic sequential processing
After any successful data base call, your data base position is immediately before
the next segment occurrence in the normal hierarchical sequence
Before your program issues any calls, position is before the root segment of the
first data base record
The GN call moves forward through the data base from the position established by
the previous call
If a GN call is unqualified (that is, if it does not employ an SSA), it returns the next
segment occurrence in the data base regardless of type, in hierarchical sequence
If a GN call includes SSAs– qualified or unqualified– DL/I retrieves only segments
that meet requirements of all SSAs you specify
If you include an unqualified SSA or omit an SSA altogether for a segment type,
DL/I allows any occurrence of that segment type to satisfy the call
But when you specify a qualified SSA, DL/I selects only those segment occurrences
The GNP Call
CALL ‘CBLTDLI’ USING
DLI-GNP
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
UNQUALIFIED-SSA.
•
•
•
Used for sequential processing within parentage
Works like the GN call, except it retrieves only segments that are subordinate to
the currently established parent
To establish parentage, your program MUST issue either a GU call or a GN call, and
the call must be successful
– Parentage is never automatically established, in
spite of the hierarchical structure of the data base
•
•
•
The segment returned by the call becomes the established parent
Subsequent GNP calls return only segment occurrences that are dependent on
that parent
When there are no more segments within the established parentage DL/I returns
GE as the status code
The GNP Call (contd.)
Vendor 1
Item 2
Established 
Parent
Item 1
Loc 2
Loc 1
Loc 5
Loc 4
Loc 3
Loc 2
Loc 1
Vendor 1
Established
 Parent
Item 2
Item 1
Loc 2
Loc 1
Fig 5.1 Sequential retrieval with GNP call
Loc 5
Loc 4
Loc 3
Loc 2
Loc 1
Status Codes you can expect during
Sequential Processing
Using Command Codes with
Retrieval Calls
•
The F command code
– When you issue a call with an SSA that includes
the F command code, the call processes the first
occurrence of the segment named by the SSA,
subject to the call’s other qualifications
– Can be used when you are doing sequential
processing and you need to back up in the data
base, or in other words, the F command code can
be used for sequential retrieval using GN and GNP
calls
– Meaningless with GU calls, because GU normally
retrieves the first segment occurrence that meets
the criteria you specify
–
Using Command Codes with
Retrieval Calls
(contd.)
The usage of the D command code is illustrated below
01 VENDOR-SSA.
05 FILLER
PIC X(11) VALUE “INVENSEG*D(”.
05 FILLER
PIC X(10) VALUE “INVENCOD =”.
05 VENDOR-SSA-CODE
PIC X(3).
05 FILLER
PIC X
VALUE “)”.
*
01 ITEM-SSA.
05 FILLER
PIC X(11) VALUE “INITMSEG*D(”.
05 FILLER
PIC X(10) VALUE “INITMNUM =”.
05 ITEM-SSA-NUMBER
PIC X(5).
05 FILLER
PIC X
VALUE “)”.
*
01 LOCATION-SSA.
05 FILLER
PIC X(11) VALUE “INLOCSEG*D(”.
05 FILLER
PIC X(10) VALUE “INLOCLOC =”.
05 LOCATION-SSA-CODE PIC X(3).
05 FILLER
PIC X
VALUE “)”.
*
01 PATH-CALL-I-O-AREA.
05 INVENTORY-VENDOR-SEGMENT
PIC X(131).
05 INVENTORY-ITEM-SEGMENT
PIC X(48).
05 INVENTORY-STOCK-LOC-SEGMENT
PIC X(21).
*
. . .
*
CALL “CBLTDLI” USING
DLI-GU
INVENTORY-PCB-MASK
•
Using Command Codes with
Retrieval Calls
(contd.)
The C command code
– If you are developing a program that retrieves just
lower-level segment occurrences from a data
base, you don’t have to code separate SSAs for
each level in the hierarchical path
– Instead you can use a single SSA with the C
command code
– Then, rather than coding a field name, relational
operator, and search value, you specify the
concatenated key for the segment you are
interested in
– An illustration of the use of the C command code
is shown below
•
Using Command Codes with
Retrieval Calls
(contd.)
The P command code
– When you issue a GU or GN call, DL/I normally
establishes parentage at the lowest level segment
that is retrieved
– However, if you want to override that and cause
parentage to be established at a higher-level
segment in the hierarchical path, you can use the
P command code in its SSA
•
The U command code
– When you use an unqualified SSA that specifies
the U command code in a GN call, DL/I restricts
the search for the segment you request to
•
Using Command Codes with
Retrieval Calls
(contd.)
The Q command code
– This command code is used to enqueue, or
reserve for exclusive use, a segment or path of
segments
– You only need to use the Q command code in an
interactive environment where there is a chance
that another program might make a change to a
segment between the time you first access it and
the time you are finished with it
Multiple Processing
•
•
Multiple processing is a general term that means a program can have more than
one position in a single physical data base at the same time
DL/I lets the programmer implement multiple processing in two ways
1.Through multiple PCBs
2.Through multiple positioning
•
Multiple PCBs
– The DBA can define multiple PCBs for a single data
base
– Then, the program has two (or more) views of the
data base
– As with PCBs for different data bases, each has its
own mask in the Linkage Section and is specified
•
Multiple Processing (contd.)
Multiple positioning
– Lets a program maintain more than one position
within a data base using a single PCB
– To do that, DL/I maintains a distinct position for each
A1
hierarchical path Data
thebaseprogram
processes
Record 1
– Most of the time, multiple
positioning is used to
C13
C12
A2
access
segments
of
two
or
more types sequentially at
B13
C11
B12
Data base
the
same time
B11
Record 2
C22
B22
B21
Fig 5.2 Two data base records to illustrate multiple positioning
C21
Multiple Processing (contd.)
MOVE ‘SEGB
’ TO UNQUAL-SSA-SEGMENT-NAME.
CALL ‘CBLTDLI’ USING
DLI-GN
SAMPLE-DB-PCB
SEGMENT-B-I-O-AREA
UNQUALIFIED-SSA.
MOVE ‘SEGC
’ TO UNQUAL-SSA-SEGMENT-NAME.
CALL ‘CBLTDLI’ USING
DLI-GN
SAMPLE-DB-PCB
SEGMENT-C-I-O-AREA
UNQUALIFIED-SSA.
– When you use multiple positioning, DL/I maintains
its separate positions based on segment type
– As a result you include an unqualified SSA in the
call that names the segment type whose position
you want to use
Module 6
Adding and Updating Data
to a Data Base
The ISRT Call
The Get Hold Calls
The REPL Call
The DLET Call
Common IMS Status Codes
The ISRT Call
•
•
•
•
The ISRT call is used to add a segment occurrence to a data base, either during
update processing of an existing data base or during load processing of a new data
base
Before an ISRT call is issued, you should first build the segment occurrence by
moving data to the fields of the segment description
After formatting the segment, you issue the ISRT call with at least one SSA: an
unqualified SSA for the segment type you want to add
Consider the example below
CALL ‘CBLTDLI’ USING
•
•
•
DLI-ISRT
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
UNQUALIFIED-SSA.
Here UNQUALIFIED-SSA specifies the segment name
Because the SSA is unqualified, DL/I tries to satisfy the call based on the current
position in the data base
As a result, you need to be careful about position when you issue an ISRT call that
specifies only a single unqualified SSA
The ISRT Call (contd.)
•
A safer technique is to specify a qualified SSA for each hierarchical level above the
one where you want to insert the segment, as illustrated below
CALL ‘CBLTDLI’ USING
•
•
•
•
DLI-ISRT
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
VENDOR-SSA
ITEM-SSA
UNQUALIFIED-SSA.
If SSAs for vendor and item are initialized with the proper key values, DL/I inserts
the new segment occurrence in the correct position in the data base
When you issue a fully qualified ISRT call like this, DL/I returns a status code of GE
if any segment occurrence you specify in an SSA isn’t present in the data base
As a result, you can issue an ISRT call with qualified SSAs instead of first issuing GU
calls to find out if higher-level segments in the path are present
By issuing one call instead of two (or more), you can save system resources
The ISRT Call (contd.)
•
Where inserted segments are stored
– If the new segment has a unique sequence field,
as most segment types do, it is added in its proper
sequential position
– However, some lower-level segment types in
some data bases have non-unique sequence fields
or don’t have sequence fields at all
– When that’s the case, where the segment
occurrence is added depends on the rules the DBA
specifies for the data base
– For a segment without a sequence field, the insert
The ISRT Call (contd.)
•
Status codes you can expect during insert processing
– GE  When you use multiple SSAs and DL/I
cannot satisfy the call with the specified path
– I I  When you try to add a segment occurrence
that is already present in the data base
– For load processing you might get status codes LB,
LC, LD or LE.
• In most cases they indicate that you are not inserting segments in exact
hierarchical sequence
• That means there is an error in your program or the files from which you
are loading the data base contain incorrect data
The Get Hold Calls
•
There are three get hold functions you can specify in a DL/I call:
1.GHU (Get hold unique)
2.GHN (Get hold next), and,
3.GHNP (Get hold next within parent)
•
•
•
These calls parallel the three retrieval calls earlier discussed
Before you can replace or delete a segment, you must declare your intent to do so,
by retrieving the segment with one of these three calls
Then you must issue the replace or delete call before you do another DL/I
processing in your program
The REPL Call
•
•
After you have retrieved a segment with one of the get hold calls, you can make
changes to the data in that segment, then issue an REPL call to replace the original
segment with the new data
There are two restrictions on the changes you can make:
1.You can’t change the length of the segment
2.You can’t change the value of the sequence field
(if the segment has one)
•
•
Never code a qualified SSA on an REPL call: if you do, the call will fail
An example of a typical replace operation is shown below
CALL ‘CBLTDLI’ USING
DLI-GHU
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
VENDOR-SSA
ITEM-SSA
LOCATION-SSA.
ADD TRANS-RECEIPT-QTY TO ISLS-QUANTITY-ON-HAND.
SUBTRACT TRANS-RECEIPT-QTY FROM ISLS-QUANTITY-ON-ORDER.
CALL ‘CBLTDLI’ USING
DLI-REPL
The REPL Call (contd.)
•
Status codes you can expect during replace processing
– If you try to use a qualified SSA on an REPL call,
you will get an AJ status code
– If your program issues a replace call without an
immediately preceding get hold call, DL/I returns a
DJ status code
– If your program makes a change to the segment’s
key field before issuing the REPL call, DL/I returns
a DA status code
The DLET Call
•
•
•
•
The DLET call works much like REPL
You must first issue a get hold call to indicate that you intend to make a change to
the segment you are retrieving
Then you issue a DLET call to delete the segment occurrence from the data base
For example, to delete a stock location that is no longer active, you’d code a series
of statements like the ones below
CALL ‘CBLTDLI’ USING
CALL ‘CBLTDLI’ USING
•
•
•
DLI-GHU
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT
VENDOR-SSA
ITEM-SSA
LOCATION-SSA.
DLI-DLET
INVENTORY-PCB-MASK
INVENTORY-STOCK-LOC-SEGMENT.
Notice that the DLET call does not include any SSAs
There is one important point you must keep in mind whenever you use the DLET
call– when you delete a segment, you automatically delete all segment
occurrences subordinate to it
The status codes you might get after a DLET call are the same as those you can get
Common IMS Status Codes
•
Returned by IMS after each DB call
– Field STATUS-CODE X(02) in the PCB-MASK definition
– Acceptable and unacceptable status codes
– ‘GE’ – record occurrence not found
– ‘GB’ – End of DB reached
•
Status codes relate to the type of IMS call
•
GHN, GHNP, GHU, GU – AB, AK, GE, GB
– AK – Invalid field name in SSA
•
ISRT – AB, AC, AD, AJ, AK, II
– AC – Segment not found
IMS Abends
•
•
•
•
•
U0456 -- PSB stopped
U0456 -- IMS Compile option ‘DLITCBL’ not set to ‘Y’
U0458 -- DB Stopped
U0844 -- DB being updated is full
S013 -- Error opening the DB
A few tips on resolving IMS abends:
• Confirm that the Abend is caused by IMS – check the job log for IMS return code
•
•
•
Check the JCL – if modified from another JCL, verify that changes are correct
Check the SYSOUT dump for IMS diagnostic messages
Use MVS/QW to get further information on the abend
Sample IMS Program
IDENTIFICATION DIVISION.
PROGRAM-ID. PATGET2.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. IBM-370.
OBJECT-COMPUTER. IBM-370.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
DATA DIVISION.
FILE SECTION.
WORKING-STORAGE SECTION.
77 TOP-PAGE
77 GET-UNIQUE
01 HOSPITAL-SSA.
05 FILLER
05 HOSPNAME-SSA
05 FILLER
01 WARD-SSA.
05 FILLER
05 WARDNO-SSA
05 FILLER
01 PATIENT-SSA.
05 FILLER
05 PATNAME-SS
05 FILLER
01 UNQUAL-HOSPITAL-SSA
01 UNQUAL-WARD-SSA
01 UNQUAL-PATIENT-SSA
01 WS-ISRT
01 WS-GHU
01 HOSP-I-O-AREA.
05 HOSP-NAME
PIC X
VALUE '1'.
PIC X(4) VALUE 'GU'.
PIC X(19) VALUE 'HOSPITAL(HOSPNAME ='.
PIC X(20).
PIC X VALUE ')'.
PIC X(19) VALUE 'WARD
PIC X(04).
PIC X VALUE ')'.
(WARDNO
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
(PATNAME ='.
X(19) VALUE 'PATIENT
X(20).
X VALUE ')'.
X(9) VALUE 'HOSPITAL
X(9) VALUE 'WARD
X(9) VALUE 'PATIENT
X(4) VALUE 'ISRT'.
X(4) VALUE 'GHU '.
PIC X(20).
'.
'.
'.
='.
Sample Program (contd.)
01 PATIENT-I-O-AREA.
03 PATIENT-NAME
03 PATIENT-ADDRESS
03 PATIENT-PHONE
03 BEDINDENT
03 DATEADMT
03 PREV-STAY-FLAG
LINKAGE SECTION.
01 PCB-MASK.
02 DBD-NAME-1
02 SEG-LEVEL-1
02 STATUS-CODE-1
02 PROCESS-OPTIONS-1
02 KEY-LENGTH
02 SEG-NAME-FDBK-1
02 LENGTH-FB-KEY-1
02 NUMB-SENS-SEGS-1
02 KEY-FB-AREA-1
PIC
PIC
PIC
PIC
PIC
PIC
X(20).
X(30).
X(10).
X(4).
X(8).
X.
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
PIC
X(8).
XX.
XX.
X(4).
S9(5) COMP.
X(8).
S9(5) COMP.
S9(5) COMP.
X(26).
PROCEDURE DIVISION.
ENTRY 'DLITCBL' USING PCB-MASK.
PERFORM INSERT-HOSP-PARA THRU INSERT-HOSP-EXIT.
PERFORM INSERT-WARD-01-PARA THRU INSERT-WARD-01-EXIT.
PERFORM INSERT-PATIENTS-PARA THRU INSERT-PATIENTS-EXIT.
GOBACK.
INSERT-HOSP-PARA.
MOVE 'MACNEAL
‘
TO HOSP-NAME.
MOVE 'ABC DDDD'
TO HOSP-ADDRESS.
MOVE '12345'
TO HOSP-PHONE.
CALL 'CBLTDLI' USING
WS-ISRT
PCB-MASK
HOSP-I-O-AREA
UNQUAL-HOSPITAL-SSA.
Sample Program (contd.)
IF STATUS-CODE-1 NOT EQUAL SPACES
EXIT.
INSERT-HOSP-EXIT.
EXIT.
INSERT-WARD-01-PARA.
MOVE '01'
MOVE 10
MOVE 20
MOVE '03'
MOVE 'INTENSIVE'
CALL 'CBLTDLI' USING WS-ISRT
TO
TO
TO
TO
TO
WARD-NO.
TOT-ROOMS.
TOT-BEDS.
BEDAVAIL
WARD-TYPE.
PCB-MASK
WARD-I-O-AREA
UNQUAL-HOSPITAL-SSA
UNQUAL-WARD-SSA.
IF STATUS-CODE-1 NOT EQUAL SPACES
EXIT.
INSERT-WARD-01-EXIT.
EXIT.
INSERT-PATIENTS-PARA.
MOVE 'MACNEAL'
MOVE 'JOHN SMITH'
MOVE '123 HAMILTON STR'
MOVE '12345
'
MOVE '1111'
MOVE '02021999'
MOVE 'N'
CALL 'CBLTDLI' USING WS-ISRT
PCB-MASK
PATIENT-I-O-AREA
HOSPITAL-SSA
WARD-SSA
UNQUAL-PATIENT-SSA.
TO
TO
TO
TO
TO
TO
TO
WARDNO-SSA.
PATIENT-NAME.
PATIENT-ADDRESS.
PATIENT-PHONE.
BEDINDENT.
DATEADMT.
PREV-STAY-FLAG.
Module 7
Secondary Indexing
The Need for Secondary Indexing
A Customer Data Base
Secondary Indexes
Secondary Keys
Secondary Data Structures
DBDGEN Requirements for Secondary Indexes
PSBGEN Requirements for Secondary Indexing
Indexing a Segment based on a Dependent Segment
The Independent AND Operator
Sparse Sequencing
Duplicate Data Fields
The Need for Secondary Indexing
•
•
•
Often you need to be able to access a data base in an order other than its primary
hierarchical sequence
Or, you may need to access a segment in a data base directly, without supplying its
complete concatenated key
With secondary indexing both are possible
A Customer Data Base
Customer
Ship-to
Buyer
Payment
Fig 7.1 The customer data base
Receivable
Adjustment
Line Item
The Customer Data Base (contd.)
01 CUSTOMER-SEGMENT.
05 CS-CUSTOMER-NUMBER
05 CS-CUSTOMER-NAME
05 CS-ADDRESS-LINE-1
05 CS-ADDRESS-LINE-2
05 CS-CITY
05 CS-STATE
05 CS-ZIP-CODE
*
01 SHIP-TO-SEGMENT.
05 STS-SHIP-TO-SEQUENCE
05 STS-SHIP-TO-NAME
05 STS-ADDRESS-LINE-1
05 STS-ADDRESS-LINE-2
05 STS-CITY
05 STS-STATE
05 STS-ZIP-CODE
*
01 BUYER-SEGMENT.
05 BS-BUYER-NAME
05 BS-TITLE
05 BS-TELEPHONE
*
01 RECEIVABLE-SEGMENT.
05 RS-INVOICE-NUMBER
05 RS-INVOICE-DATE
05 RS-PO-NUMBER
05 RS-PRODUCT-TOTAL
PIC
PIC
PIC
PIC
PIC
PIC
PIC
X(6).
X(31).
X(31).
X(31).
X(18).
XX.
X(9).
PIC
PIC
PIC
PIC
PIC
PIC
PIC
XX.
X(31).
X(31).
X(31).
X(18).
XX.
X(9).
PIC X(31).
PIC X(31).
PIC X(10).
PIC
PIC
PIC
PIC
X(6).
X(6).
X(25).
S9(5)V99
COMP-3.
The Customer Data Base (contd.)
01 PAYMENT-SEGMENT.
05 PS-CHECK-NUMBER
05 PS-BANK-NUMBER
05 PS-PAYMENT-DATE
05 PS-PAYMENT-AMOUNT
*
01 ADJUSTMENT-SEGMENT.
05 AS-REFERENCE-NUMBER
05 AS-ADJUSTMENT-DATE
05 AS-ADJUSTMENT-TYPE
05 AS-ADJUSTMENT-AMOUNT
*
01 LINE-ITEM-SEGMENT.
05 LIS-ITEM-KEY.
10 LIS-ITEM-KEY-VENDOR
10 LIS-ITEM-KEY-NUMBER
05 LIS-UNIT-PRICE
05 LIS-QUANTITY
*
PIC
PIC
PIC
PIC
X(16).
X(25).
X(6).
S9(5)V99
COMP-3.
PIC
PIC
PIC
PIC
X(16).
X(6).
X.
S9(5)V99
COMP-3.
PIC
PIC
PIC
PIC
X(3).
X(3).
S9(5)V99
S9(7)
COMP-3.
COMP-3.
Fig 7.2 Segment Layouts for the Customer Data Base (Part 2 of 2)
Customer Data Base
Secondary Indexes
Secondary Index
Data Base
Invoice number index data base
Prefix
Data
Invoice
Rec. Seg.
Index
No.
Addr.
Pointer
Segment
Customer
Ship-to
Index Target
Segment
Buyer
Payment
Index Source
Segment
Receivable
Adjustment
Line Item
Indexed Data Base
Fig 7.3 Secondary Indexing Example in which the Index Source Segment and the Index Target Segment are the same
•
•
•
•
•
•
•
Secondary
Indexes
(contd.)
DL/I maintains the alternate sequence by storing pointers to segments of the indexed
data base in a separate index data base
A secondary index data base has just one segment type, called the index pointer
segment
The index pointer segment contains two main elements– a prefix element and a data
element
The data element contains the key value from the segment in the indexed data base
over which the index is built, called the index source segment
The prefix part of the index pointer segment contains a pointer to the index target
segment– the segment that is accessible via the secondary index
The index source and target segments need not be the same
After a secondary index has been set up, DL/I maintains it automatically as changes are
made to the indexed data base– though the index is transparent to application
programs that use it
– So, even if a program that is not sensitive to a
secondary index updates a data base record in a way
that would affect the index, DL/I automatically
Secondary Indexes (contd.)
•
If multiple access paths are required into the same data base, the DBA can define
as many different secondary indexes as necessary– each stored in a separate index
data base
– In practice, the number of secondary indexes for a
given data base is kept low because each imposes
additional processing overhead on DL/I
Secondary Keys
•
•
•
The field in the index source segment over which the secondary index is built is
called the secondary key
The secondary key need not be the segment’s sequence field– any field can be
used as a secondary key
Though usually, a single field within the index source segment is designated as the
secondary key for a secondary index, the DBA can combine as many as five fields in
the source segment to form the complete secondary key
– These fields need not even lie adjacent to each
other
•
Secondary key values do not have to be unique
•
•
•
•
Secondary
Data
Structures
A secondary index changes the apparent hierarchical structure of the data base
The index target segment is presented to your program as if it were a root segment,
even if it isn’t actually the root segment
As a result, the hierarchical sequence of the segments in the path from the index target
segment to the root segment is inverted: those segments appear to be subordinate to
the index target segment, even though they are actually superior to it
The resulting rearrangement of the data base structure is called a secondary data
structure
Receivable
Ship-to
Customer
Payment
Buyer
Fig 7.4 Secondary Data Structure for the Secondary Index
Adjustment
Line Item
Secondary Data Structures (contd.)
•
Secondary data structures don’t change the way the data base segments are
stored on disk
– They just alter the way DL/I presents those
segments to application programs
•
When you code an application program that processes a data base via a secondary
index, you must consider how the secondary data structure affects your program’s
logic
•
DBDGEN Requirements for
Because a secondary index relationship involves two data bases, two DBDGENs are
Secondary
Indexes
required– one for the indexed data base and the other for the secondary index data
base
Fig 7.5 Partial DBDGEN output for the customer data base showing the code to implement the secondary index
DBDGEN Requirements for
Secondary Indexes (contd.)
Fig 7.6 DBDGEN output for the Secondary Index Data Base
•
•
In the DBDGEN for the indexed data base, an LCHILD macro relates an index target segment to its
associated secondary index data base
In the DBDGEN for the secondary index data base, an LCHILD macro relates the index pointer
segment to the index target segment
DBDGEN Requirements for
Secondary Indexes (contd.)
•
•
•
ACCESS=INDEX in the DBD macro in Fig 7.6 tells DL/I that an index data base is
being defined
The INDEX parameter of the LCHILD macro in Fig 7.6 specifies the name of the
secondary key field– CRRECXNO
The XDFLD macro in Fig 7.5 supplies a field name (CRRECXNO) that is used to
access the data base via the secondary key
– This key field does not become a part of the
segment
– Instead, its value is derived from up to five fields
defined within the segment with FIELD macros
•
The SRCH parameter defines the field(s) that constitute the secondary index
•
•
•
•
PSBGEN Requirements for
Just because a secondary index exists for a data base doesn’t mean DL/I will
Secondary
Indexing
automatically use it when one of your programs issues calls for that data base
You need to be sure that the PSBGEN for the program specifies the proper processing
sequence for the data base on the PROCSEQ parameter of the PSB macro
If it doesn’t, processing is done using the normal hierarchical sequence for the data
base
For the PROCSEQ parameter, the DBA codes the DBD name for the secondary index
data base that will be used
Fig 7.7 PSBGEN Output
PSBGEN Requirements for
Secondary Indexing (contd.)
•
•
•
The SENSEG macros in Fig 7.7 reflect the secondary data structure imposed by the
secondary index
When the PROCSEQ parameter is present, processing is done based on the
secondary index sequence
If a program needs to access the same indexed data base using different
processing sequences, the program’s PSBGEN will contain more than one PCB
macro, each specifying a different value for the PROCSEQ parameter
Indexing a Segment
based on a Dependent Segment
Secondary Index Data Base
Invoice number index data base
Customer Data Base
Index Target
Segment
Customer
Prefix
Cust. Seg.
Addr.
Data
Item
No.
Ship-to
Buyer
Index
Pointer
Segment
Receivable
Index Source
Segment
Payment
Adjustment
Line Item
Indexed Data Base
Fig 7.8 Secondary Indexing Example in which the Index Source Segment and the Index Target
Segment are different
•
•
Indexing a Segment
based on a Dependent Segment
(contd.)
The Index Source Segment and the Index Target Segment need not be the same
Some applications require that a particular segment be indexed by a value that is
derived from a dependent segment
– In such a case, the Index Target Segment and the
Index Source Segment are different
– For example, in Fig 7.8, you can retrieve customers
based on items they have purchased
– In other words, the SSA for a get call would specify
an item number, but the call would retrieve a
customer segment
•
The only restriction you need to be aware of here is that the Index Source Segment
must be a dependent of the Index Target Segment
– Thus, in the example shown in Fig 7.8, it wouldn’t
The Independent AND Operator
•
•
•
•
•
•
When used with secondary indexes, AND ( * or & ) is called the dependent AND operator
The independent AND (#) lets you specify qualifications that would be impossible with the
dependent AND
This operator can be used only for secondary indexes where the index source segment is a
dependent of the index target segment
Then, you can code an SSA with the independent AND to specify that an occurrence of the
target segment be processed based on fields in two or more dependent source segments
In contrast, a dependent AND requires that all fields you specify in the SSA be in the same
segment occurrence
An SSA that uses the independent AND operator is shown below
01 ITEM-SELECTION-SSA.
*
05 FILLER
05 FILLER
05 SSA-ITEM-KEY-1
05 FILLER
05 FILLER
05 SSA-ITEM-KEY-2
05 FILLER
PIC X(9) VALUE ‘CRCUSSEG(’.
PIC X(10) VALUE ‘CRLINXNO =’.
PIC X(8).
PIC X
VALUE ‘#’.
PIC X(10) VALUE ‘CRLINXNO =’.
PIC X(8).
PIC X
VALUE ‘)’.
•
•
•
•
•
•
•
Sparse
Sequencing
When the DBA implements a secondary index data base with sparse sequencing (also
called sparse indexing), it is possible to omit some index source segments from the
index
Sparse sequencing can improve performance when some occurrences of the index
source segment must be indexed but others need not be
DL/I uses a suppression value, a suppression routine, or both to determine whether a
segment should be indexed (either when inserting a new segment or processing an
existing one)
If the value of the sequence field(s) in the index source segment matches a suppression
value specified by the DBA, no index relationship is established (for an insert) or
expected (for any other call)
The DBA can also specify a suppression routine that DL/I invokes to determine the index
status for the segment
The suppression routine is a user-written program that evaluates the segment and
determines whether or not it should be indexed
Note:
– When sparse indexing is used, its functions are
handled by DL/I
– You don’t need to make special provisions for it in
Duplicate Data Fields
•
•
•
•
•
For some applications, it might be desirable to store user data from the index
source segment in the index pointer segment
When the DBA specifies that some fields are duplicate data fields, this is possible
Up to five data fields can be stored in the index data base, and DL/I maintains
them automatically
Duplicate data fields are useful only when the index data base is processed as a
separate data base
Note:
– Duplicate data fields impose extra DL/I overhead
and require extra DASD storage
– It is the DBA’s responsibility to decide whether the
advantages of using duplicate data fields outweigh
the extra DL/I overhead and DASD storage
requirements mentioned above
Module 8
Logical Data Bases
Introduction to Logical Data Bases
Logical Data Base Terminology
DBDGENs for Logical Data Bases
An Introduction to Logical Data
Inter related databases
Bases
A logical child segment has 2 parent segments
• One
Inter
related databases.
physical
parent and one logical parent
DB2
SEG-1
DB1
PP
Physical
Parent
LP
SEG-a
SEG-b
Logical Parent
RLC
Real
Logical
Child
C2
VLC
Virtual
Logical Child
Logical Data Base Terminology
•
Real Logical Child
– The child under consideration
•
Physical Parent
– Original parent of the child
•
Logical Parent
– The parent in the other data base
•
Virtual Logical Child
– The child as seen from the other data base
•
Three types of Logical data bases
– Unidirectional.
DBDGENs for a Logical Data Base
******DBD1******
.
.
.
6
SEGM NAME=RLC,
7
PARENT=(PP,PTR), (LP,DBD2),
8
POINTER=(TWIN,LTWIN), RULES=(LLV,LAST),BYTES=16
9
FIELD NAME=********************************
10 FIELD NAME=********************************
.
.
.
******DBD2*******
.
.
.
6
SEGM NAME=LP, PARENT=SEG-1, BYTES=48
7
LCHILD NAME= (RLC,DBD1), POINTER=PTR, PAIR=VLC
8
FIELD NAME=********************************
9
FIELD NAME=********************************
10
FIELD NAME=********************************
Module 9
Recovery and Restart
Introduction to Data Base Recovery
Introduction to Checkpointing
Types of Checkpointing
Extended Restart
Database Image Copy
Introduction to Data Base Recovery
•
•
•
The process of recovering the data base in case of application program failure
Back out changes made by the abended program, correct the error and rerun the
program.
Types of recoveries
– Forward recovery
– Backward recovery
•
Forward Recovery
– Data base changes for a time period is
accumulated
– A copy of the data base is created
– The changes are applied to this data base copy
– DL/I uses change-data stored in DL/I logs for
Introduction to Checkpointing
•
•
•
•
•
•
•
Synonyms: synchronization point, sync point, commit point and point of integrity
Program execution point at which the DB changes are complete and accurate
DB changes made before the most recent checkpoint are not reversed by recovery
Normally the start of the pgm is considered as a default checkpoint
In case of a number of DB updates, explicit checkpoints can be specified
Explicit checkpoints can be established using checkpoint call(CHKP) inside the
program
CHKP creates a checkpoint record on DL/I log which prevents recovery before that
point
Types of Checkpointing
•
Types of checkpointing
– Basic checkpointing
– Symbolic checkpointing
•
Basic checkpointing
– Simple form of checkpointing.
– Issues checkpoint calls that the DL/I recovery
utilities use during recovery processing
•
Symbolic checkpointing
– More advanced type of checkpointing
– Used in combination with extended restart
– Programs resume from the point following the
Extended Restart (XRST)
•
•
•
•
•
•
•
•
•
The XRST call is used in connection with the symbolic checkpoint call
It is used to restart your program
The XRST call precedes a symbolic checkpoint call
The XRST call must be issued only once
It should be issued early in the execution of the program
It must precede any CHKP call
The program is restarted from a symbolic CHKP taken during a previous execution
of the program
The CHKP used to perform the restart can be identified by entering the checkpoint
ID
CHKP ID can be specified in 2 ways
– In the I/O area pointed to by the XRST call
– Specifying ID in the CKPTID= field of EXEC
statement in the program's JCL
Database Image Copy
•
Job which is run to take backup copies of IMS database datasets at periodic
intervals
– Traditionally, batch cycle starts at 7 pm and ends
at 7 am
– Image Copy jobs are usually run before and after a
batch cycle
– If abend occurs, revert to the DB generated by
image copy job and rerun
– Commonly used image copy utility is BMC
Software’s ICPUMAIN
– Database and Image copy DD names specified in
the ICPSYSIN card
Module 10
DL/I Data Base Organizations
DL/I Organizations & Access Methods
Hierarchical Sequential Organization
Hierarchical Direct Organization
Additional IMS Access Methods
DL/I Organizations & Access
Methods
•
•
File Organization is a description of how a file is processed & Access Method is the
software used to implement that processing.
DL/I provides two basic data base organizations :
– Hierarchic Sequential: In this the segments that
make up the database record are related to one
another by their physical locations.
– Hierarchic Direct : In this the segment occurrences
include prefixes that contain direct pointers to
related segments.
Hierarchic Sequential Organizations
Access Methods
•
HS Organizations provide four types of Access Methods
– HSAM ( Hierarchic Sequential Access Method) :
The program in HSAM database works through it
sequentially from beginning to end.The
application programs cannot replace or delete
segments without copying the entire database.
– HISAM (Hierarchic Indexed Sequential Access
Method): In HISAM the data is stored with
hierarchic sequential organization. An index is also
maintained to allow random access to any
database record.
– SHSAM( Simple Hierarchical Sequential Access
Hierarchic Direct Organization
Access Method
•
HDAM ( Hierarchic Direct Access Method ):
– HDAM stores root segment occurrences based on
a randomizing routine.
– Occurrences of dependent segments are related
to root and one another by a system of pointers
the HD Organization is based upon.
– HDAM databases are not appropriate for
sequential processing.
•
HIDAM (Hierarchic Indexed Direct Access Method) :
– Segment data in HIDAM is stored in the same way
like that in HDAM.
Additional IMS Access Methods
•
GSAM( Generalized Sequential Access Methods):
– GSAM lets application files to be treat OS
sequential files as databases.
– Data is processed on a record to record to basis
but through DL/I calls.
– Processing of database is sequential , ISRT add
data only at the end of database & REPL and DLET
calls are not supported.
– They are typically used during conversion from a
system that uses standard files to one that uses
data bases.
Additional IMS Access Methods
(contd..)
•
DEDB( Data Entry Data Base ) :
– DEBD is stored in disk and has a hierarchical
structure
– They are organized in typical DL/I fashion, as
direct dependent segment types.
– DEBD’s use a complicated storage scheme that
involves separating the data base into as many as
240 areas and this allows very large data bases.
Module 11
Advanced DL/I features
Variable Length Segments
DBD for GSAMs
PCB for GSAMs
Variable Length Segments
•
•
•
•
When a field length that is stored in a segment type varies, for example
Description or Explanatory text, then we define those fields as variable length
fields
The segment with such a field defined in it is called Variable Length Segment
For description and explanatory fields, if we define them long enough to
accommodate the longest possible text, then a lot of space is wasted in cases
where it contains shorter strings.
The SEGM macro in DBD is defined as
SEGM
•
•
NAME=INVENSEG,PARENT=0,POINTER=TR,BYTES=m,n
• m=maximum length of the segment + 2 bytes
• n=minimum length of the segment + 2 bytes
The extra two bytes is used to store the length field of the occurrence of the
variable length segment
In Application Program :
– The length field has to be included in the I-O Area
for the segment. Length PIC S 9(4)
Variable Length Segments (contd.)
•
Variable Length Segments are appropriate when segment occurrence length vary
but once created and made stabilized.
•
Disadvantage:
– If the occurrence of the segment type grows in
length then Variable length segment will drop
performance
– When segment type occurrences grow in size then
it split's into 2 parts which are not stored in the
same physical record, so we require two I/O
operations to fetch the segment therefore the
DBD for GSAMs
•
•
•
During DBD generation for a GSAM database we should specify one dataset group
The DD name of the input dataset that is used when the application retrieves data
from the database
The DD name of the output dataset used when loading the database.
•
The DBD for a GSAM is shown below
DBD NAME=CARDS,ACCESS=(GSAM,BSAM)
DATASET D1=ICARDS,DD2=OCARDS,RECFM=F,RECORD=80
DBDGEN
FINISH
END
•
In GSAM DBD's you can't specify
– SEGM and FIELD statements
– The use of logical or index relationships between
segments
•
IMS adds 2 bytes to the record length value specified in the DBD in order to
DBD for GSAMs (contd.)
•
•
•
•
Whenever the database is GSAM/BSAM and the records are variable (V or VB), IMS
adds 2 bytes.
The record size of the GSAM database is 2 bytes greater than the longest segment
that is passed to IMS by the application program.
A database if defined as GSAM has the advantage of the usage of CHECKPOINT and
RESTART
Disadvantage of GSAM database : Only inserts can be done to the DB which is
defined as GSAM, no delete operation can be performed on GSAM Database.
PCB for GSAMs
•
•
The PCB for a GSAM database is coded as shown below
PCB
TYPE=GSAM,DBDNAME=REPORT,PROCOPT=LS
The GSAM PCB statement must follow the PCB statements with TYPE=TP or DB if
any exist in the PSB generation, the rule is:
– TP PCBs First
– DB PCBs Second
– GSAM PCBs Last
•
A sample PSB is shown below
PCB TYPE=TP,NAME=OUTPUT1
PCB TYPE=DB,DBDNAME=PARTMSTR,PROCOPT=A,KEYLEN=100
SENSEG NAME=PARTMAST,PARENT=0,PROCOPT=A
SENSEG NAME=CPWS,PARENT=PARTMAST,PROCOPT=A
PCB TYPE=GSAM,DBDNAME=REPORT,PROCOPT=LS
PSBGEN LANG=COBOL,PSBNAME=APPLPGM3
END
Thank You