Page : 1/128

IMS DBIMS DB

Page : 2/128

ObjectivesObjectives

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.

Page : 3/128

PrerequisitesPrerequisites

Knowledge of COBOL

Basic knowledge of data base management concepts

Page : 4/128

Course OutlineCourse Outline

1. An Introduction to DL/I Data Bases

2. DL/I Programs and Control Blocks

3. COBOL Basics for Processing a DL/I Data Base

4. Segment Search Arguments : How to use them

5. Data retrieval from an IMS Data Base

6. Adding and Updating Data to a Data Base

7. Secondary Indexing

8. Logical Data Bases

9. Recovery and Restart

10. DL/I Data Base Organizations

11. Advanced DL/I features

Page : 5/128

ReferencesReferences

IMS for the COBOL ProgrammerPart 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

Page : 6/128

Module 1Module 1An Introduction to DL/I Data An Introduction to DL/I Data

BasesBases

Hierarchical Structures

Why a Data Base Management System

Basic DL/I Terminology

Basic DL/I Data Base Processing

Page : 7/128

Hierarchical StructuresHierarchical 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.

Page : 8/128

Why a data base management Why a data base management system?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

Page : 9/128

Basic DL/I TerminologyBasic DL/I Terminology

SegmentA 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

ADDRESS

House Number

Street

Name

City State Country Zip Code

Fig 1.3 The ADDRESS segment with six fields

Segment TypeA category of data

There can be a maximum of 255 segment types and 15 levels in one data base

Segment OccurrenceOne 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 definition- but 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

Page : 10/128

Basic DL/I Terminology (contd.)Basic DL/I Terminology (contd.)

* 01 INVENTORY-VENDOR-SEGMENT. 05 IVS-VENDOR-CODE PIC X(3). 05 IVS-VENDOR-NAME PIC X(30). 05 IVS-VENDOR-ADDRESS PIC X(30). 05 IVS-VENDOR-CITY PIC X (17). 05 IVS-VENDOR-STATE PIC XX. 05 IVS-VENDOR-ZIP-CODE PIC X(9). 05 IVS-VENDOR-TELEPHONE PIC X(10).*  01 INVENTORY-ITEM-SEGMENT. 05 IIS-NUMBER PIC X(5). 05 IIS-DESCRIPTION PIC X(35). 05 IIS-UNIT-PRICE PIC S9(5)V99 COMP-3. 05 IIS-AVG-UNIT-COST PIC S9(5)V99 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.*

Fig 1.5 Segment layouts for the Inventory data base

Vendor

Item

Stock Location

Fig 1.4 The hierarchical structure of the Inventory data base with three segment types

Page : 11/128

Basic DL/I Terminology (contd.)Basic DL/I Terminology (contd.)

Root SegmentThe segment type at the top of a hierarchy

Data base recordEach occurrence of the root segment plus all the segment occurrences that are subordinate to it make up one data base record

Every data base record has one and only one root segment, although it may have any number of subordinate segment occurrences

Data base Record 1

Data base Record 2

Vendor 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Vendor 2

Item 1

Loc 2

Loc 1

Fig 1.6 Two data base records from the Inventory data base

Page : 12/128

Basic DL/I Terminology (contd.)Basic DL/I Terminology (contd.)

Dependent SegmentA segment other than the root segment in a data base record

Accessible only through one or more “parent” segments

Parent SegmentA segment that has one or more dependent segments

Child SegmentEvery dependent segment in a hierarchy

Twin SegmentTwo or more segment occurrences of the same type and with the same segment occurrence as their parent

PathSeries of segments leading from the root segment occurrence down to any specific segment occurrence

Must be continuous- intermediate levels can’t be skipped

Page : 13/128

Basic DL/I Terminology (contd.)Basic DL/I Terminology (contd.)

Key or Sequence FieldThe 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 fieldsUsed to search through the DB for particular values

Max 255 search fields in a segment

Concatenated fieldKey formed to access a particular segment

Concatenation of keys of root segment and all successive children down to the accessed segment

Undefined fieldsFields not defined to IMS

Format determined by the program loading the DB

Page : 14/128

Basic DL/I Terminology (contd.)Basic DL/I Terminology (contd.)

Logical data basesAdditional relationships within one physical data base

Fig 1.7 A logical relationship can connect two data bases

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

Customer

Ship-to

Buyer Receivable

Payment Adjustment Line ItemStock

Location

Item

Vendor

Page : 15/128

Basic DL/I Data Base ProcessingBasic DL/I Data Base Processing

Sequential ProcessingTop –> Down, Left -> Right

PositionAt 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

Data base Record 1

Data base Record 2

Vendor 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Vendor 2

Item 1

Loc 2

Loc 1

Fig 1.8 Sequential processing

Page : 16/128

Basic DL/I Data Base Processing Basic DL/I Data Base Processing (contd.)(contd.)

Random (Direct) ProcessingKey (sequence) field required

Concatenated KeyCompletely identifies the path from the root segment to the segment you want to retrieve.

Concatenated Key:

Vendor 2

Item 1

Location 1

Fig 1.9 Random Processing

Data base Record 1

Data base Record 2

Vendor 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Vendor 2

Item 1

Loc 2

Loc 1

Page : 17/128

Module 2Module 2DL/I Programs and Control DL/I Programs and Control

BlocksBlocks

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

Page : 18/128

The IMS Software EnvironmentThe IMS Software Environment

ApplicationPrograms

IMS ControlBlocks

DL/I

OS

Data Base

IMS DC RemoteTerminal

Fig 2.1 The IMS Software Environment

Page : 19/128

How DL/I relates toHow DL/I relates toyour application programsyour application programs

ApplicationProgram

Operating SystemAccess Method

(eg. VSAM)

FileData Set

Standard File Processing

ApplicationProgram

DL/I Data Base Processing

DL/I

Operating SystemAccess Method

(eg. VSAM)

Data BaseData Set

Fig 2.2 Standard file processing compared to DL/I data base processing

Page : 20/128

How DL/I relatesHow DL/I relatesto your application programs to your application programs

(contd.)(contd.)

Standard file processingStandard 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 processingDLI - 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.

Page : 21/128

Control BlocksControl 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

Page : 22/128

SAMPLE DBDGEN (Explained in next SAMPLE DBDGEN (Explained in next slide)slide)

STMT SOURCE STATEMENT1 PRINT NOGEN2 DBD NAME=INDBD,ACCESS=HIDAM3 DATASET DD1=IN,DEVICE=33804 **/ 3380 DISK STORAGE5 *6 SEGM NAME=INVENSEG, PARENT=0,POINTER=TB,BYTES=1317 LCHILD NAME=(INPXPNTR,INPXDBD),POINTER=INDX8 FIELD NAME=(INVENCOD,SEQ),BYTES=3,START=1,TYPE=C9 FIELD NAME=INVENNAM,BYTES=30,START=4,TYPE=C10 FIELD NAME=INVENADR,BYTES=30,START=34,TYPE=C11 FIELD NAME=INVENCIT,BYTES=17,START=64,TYPE=C12 FIELD NAME=INVENSTA,BYTES=2,START=81,TYPE=C13 FIELD NAME=INVENZIP,BYTES=9,START=83,TYPE=C14 FIELD NAME=INVENTEL,BYTES=10,START=92,TYPE=C15 FIELD NAME=INVENCON,BYTES=30,START=102,TYPE=C16 *17 SEGM NAME=INITMSEG,PARENT=INVENSEG,BYTES=4818 FIELD NAME=(INITMNUM,SEQ),BYTES=5,START=1,TYPE=C19 FIELD NAME=INITMDES,BYTES=35,START=6,TYPE=C20 FIELD NAME=INITMPRC,BYTES=4,START=41,TYPE=P21 FIELD NAME=INITMCST,BYTES=4,START=45,TYPE=P22 *23 SEGM NAME=INLOCSEG, PARENT=INITMSEG,BYTES=2124 FIELD NAME=(INLOCLOC,SEQ),BYTES=3,START=1,TYPE=C25 FIELD NAME=INLOCONH,BYTES=4,START=4,TYPE=P26 FIELD NAME=INLOCROP,BYTES=4,START=8,TYPE=P27 FIELD NAME=INLOCONO,BYTES=4,START=12,TYPE=P28 FIELD NAME=INLOCDAT,BYTES=6,START=16,TYPE=C29 *30 DBDGEN72 **/**************************************************************************73 **/ RECOMMENDED VSAM DEFINE CLUSTER PARAMETERS74 **/**************************************************************************75 **/* *NOTE276 **/* DEFINE CLUSTER (NAME(IN) NONINDEXED -77 **/* RECORDSIZE (2041,2041) -78 **/* COUNTERINTERVALSIZE (2048))79 **/* *NOTE2 - SHOULD SPECIFY DSNNAME FOR DD IN80 **/**************************************************************************162 **/***********SEQUENCE FIELD*************211 **/***********SEQUENCE FIELD*************325 FINISH

326 END Fig 2.3 Assembler source listing for the Inventory data base DBDGEN

Page : 23/128

SAMPLE DBDGEN (contd.)SAMPLE DBDGEN (contd.)

Explanation of Fig 2.3First 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

Page : 24/128

DBDGEN (contd.)DBDGEN (contd.)

FIELD macro defines a field in the DBSTART 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

SEQ parameter specifies a sequence fieldsegment occurrences are added in sequence by values in these fields

Fig 2.4 FIELD macro TYPE parameter codes

Page : 25/128

SAMPLE PSBGENSAMPLE PSBGEN

STMT SOURCE STATEMENT1 PRINT NOGEN2 PCB TYPE=DB,DBDNAME=INDBD,PROCOPT=LS3 SENSEG NAME=INVENSEG4 SENSEG NAME=INITMSEG,PARENT=INVENSEG5 SENSEG NAME=INLOCSEG,PARENT=INITMSEG6 PSBGEN PSBNAME=INLOAD,LANG=COBOL87 END

Fig 2.5 Assembler source listing for the Inventory data base load program’s PSBGEN

Explanation of Fig 2.5PCB (Program Communication Block) refers to one data base.

One PCB macro for each database accessed

Segment Level SensitivityA 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 sensitivityWhen the program accesses that segment, only sensitive fields are presented

Page : 26/128

PSBGEN (contd.)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 macroIndicates 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.

Page : 27/128

IMS Processing OptionsIMS Processing Options

Indicates to IMS the type of access allowed for a sensitive segment (SENSEG)

Commonly used Processing OptionsPROCOPT=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 !

Page : 28/128

ACB & ACBGENACB & 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.

Page : 29/128

Running an application program Running an application program under DL/I under DL/I

Batch program does not access IMS directlyJCL invokes the DL/I ‘batch initialization module’ DFSRRC00 which loads the application program and the required DL/I modulesThe program and DL/I modules execute togetherSample 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'

Page : 30/128

SAMPLE JCL (Contd.)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=*

Page : 31/128

Module 3Module 3COBOL Basics for Processing aCOBOL Basics for Processing a

DL/I Data BaseDL/I Data Base

The ENTRY and GO BACK Statements

The DL/I Call

The PCB Mask

Page : 32/128

ENTRY andENTRY andGO BACK StatementsGO 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 statementPCB masks should be listed on the ENTRY statement in the same sequence as they appear in your program’s PSBGEN

GO BACK StatementWhen a program ends, it passes control back to the DL/I

DL/I reallocates resources and closes the data base data sets

Use GO BACK and not a STOP RUN statement

Page : 33/128

The DL/I CallThe 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-functionPCB-masksegment-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

Page : 34/128

The DL/I Call (contd.)The DL/I Call (contd.)

The DL/I FunctionFirst parameter coded on any DL/I call

Four character working storage field containing the function code

01 DLI-FUNCTIONS. 05 DLI-GU PIC X(4) VALUE ‘GU ’. 05 DLI-GHU PIC X(4) VALUE ‘GHU ’. 05 DLI-GN PIC X(4) VALUE ‘GN ’. 05 DLI-GHN PIC X(4) VALUE ‘GHN ’. 05 DLI-GNP PIC X(4) VALUE ‘GNP ’. 05 DLI-GHNP PIC X(4) VALUE ‘GHNP’. 05 DLI-ISRT PIC X(4) VALUE ‘ISRT’. 05 DLI-DLET PIC X(4) VALUE ‘DLET’. 05 DLI-REPL PIC X(4) VALUE ‘REPL’. 05 DLI-CHKP PIC X(4) VALUE ‘CHKP’. 05 DLI-XRST PIC X(4) VALUE ‘XRST’. 05 DLI-PCB PIC X(4) VALUE ‘PCB ’.

Fig 3.3 DL/I function codes

COBOL doesn’t allow coding literals in a CALL statement

Page : 35/128

The DL/I Call (contd.)The DL/I Call (contd.)

Get functionsFirst 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 functionsUsed to change data in the data base

ISRT or the ‘insert’ function is used to add a new segment occurrence to a data base– whether it be change an existing data base or to load a new one

DLET or the ‘delete’ function is used to remove a segment from a data base

REPL or the ‘replace’ function is used to replace a segment occurrence

Page : 36/128

The DL/I Call (contd.)The DL/I Call (contd.)

Other functionsFunctions 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)

Page : 37/128

The DL/I Call (contd.)The DL/I Call (contd.)

PCB maskSecond 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 AreaThird parameter on the DL/I call

Name of the working storage field into which DL/I will return retrieved data or from which it will get data for an update operation

Page : 38/128

The DL/I Call (contd.)The DL/I Call (contd.)

Segment search argumentOptional 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 SSASupplies 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 SSACombines a segment name with additional information that specifies the segment occurrence to be processed

A GU call with a qualified SSA might request a particular occurrence of a named segment type by providing a key value

Page : 39/128

The PCB MaskThe 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 PIC X(8). 05 IPCB-SEGMENT-LEVEL PIC XX. 05 IPCB-STATUS-CODE PIC XX. 05 IPCB-PROC-OPTIONS PIC X(4). 05 FILLER PIC S9(5) COMP. 05 IPCB-SEGMENT-NAME PIC X(8). 05 IPCB-KEY-LENGTH PIC S9(5) COMP. 05 IPCB-NUMB-SENS-SEGS PIC S9(5) COMP. 05 IPCB-KEY PIC X(11).

Fig 3.4 PCB mask for an Inventory data base

Page : 40/128

The PCB Mask (contd.)The PCB Mask (contd.)

Data base nameThe name of the data base being processed

Segment levelSpecifies 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 codeContains 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 in the PCB

If a call is unsuccessful or raises some condition that isn’t normal, DL/I moves some non-blank value to the status code field

It is good programming practice to evaluate the status code after you issue a DL/I call

Processing options (would be elaborated later)Indicates the processing a program is allowed to do on the data base

Segment name feedback areaThe name of the segment is stored by DL/I in this field after each DL/I call.

Page : 41/128

The PCB Mask (contd.)The PCB Mask (contd.)

Key length feedback areaThe 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 segmentsContains the number of SENSEG macros subordinate to the PCB macro for this data base

Key feedback areaVaries 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 data base

After a data base operation, DL/I returns the concatenated key of he lowest level segment processed in this field, and it returns the key’s length in the key length feedback area

Page : 42/128

Module 4Module 4Segment Search ArgumentsSegment Search Arguments

Types of SSAs

Basic Unqualified SSA

Basic Qualified SSA

Command Codes

The Null Command Code

Path Call

Multiple Qualifications

Page : 43/128

Types of SSAsTypes of SSAs

SSA identifies the segment occurrence you want to access

It can be eitherQualified

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

You can code as many SSAs on a single call as you need

You can combine qualified and unqualified SSAs on a single call

Page : 44/128

Basic Unqualified SSABasic Unqualified SSA

01 UNQUALIFIED-SSA.* 05 UNQUAL-SSA-SEGMENT-NAME PIC X(8). 05 FILLER 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 kind of SSA you are providing

Page : 45/128

Basic Unqualified SSA (contd.)Basic Unqualified SSA (contd.)

To access a particular segment type, you must modify the segment name during program execution, by moving an appropriate eight-character segment name to the field UNQUAL-SSA-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

For example,

01 UNQUAL-VENDOR-SSA PIC X(9) VALUE ‘INVENSEG ’.* 01 UNQUAL-ITEM-SSA PIC X(9) VALUE ‘INITMSEG ’.* 01 UNQUAL-STOCK-LOC-SSA PIC X(9) VALUE ‘INVENSEG ’.

Page : 46/128

Basic Qualified SSABasic Qualified SSA

01 VENDOR-SSA.* 05 FILLER PIC X(9) VALUE ‘INVENSEG(’. 05 FILLER PIC X(10) VALUE ‘INVENCOD =’. 05 VENDOR-SSA-CODE PIC X(3). 05 FILLER PIC 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

Page : 47/128

Basic Qualified SSA (contd.)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 EQ = =Not equal to NE <>Greater Than GT > >Greater than or Equal to GE >= =>Less Than LT < <Less than or Equal to LE <= =< 

After the relational operator, you code a variable field into which you move the search value you want to use for the call

The length of the search value field can vary depending on the size of the field in the segment– it is the only part of a basic qualified SSA that doesn’t have a fixed length

The last character in the qualified SSA is a right parenthesis

Page : 48/128

Command CodesCommand Codes

Fig 4.4 Qualified SSA format with a single command code

Command are used in SSAs for three purposesTo extend DL/I functionality

To simplify programs by reducing the number of DL/I calls

For performance improvement resulting from the reduced number of DL/I calls

Fig 4.3 Unqualified SSA format with a single command code

Page : 49/128

Command Codes (contd.)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 PIC X(8). 05 FILLER PIC X VALUE “*”. 05 UNQUAL-SSA-COMMAND-CODE PIC X. 05 FILLER PIC X VALUE SPACE.*

Page : 50/128

Command Codes (contd.)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

Page : 51/128

The Null Command CodeThe 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 PIC X(8). 05 FILLER PIC X VALUE “*”. 05 UNQUAL-SSA-COMMAND-CODE PIC X VALUE “-”. 05 FILLER PIC X VALUE SPACE.*

Page : 52/128

Path CallPath 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 segmentConsider 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 programSuch 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.

Page : 53/128

Multiple QualificationsMultiple 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 itWhen 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 OREither of the two symbols shown in the table below may be used for AND or ORThe independent AND operator is used for special operations with secondary indexes and will be discussed later

Page : 54/128

Multiple Qualifications (contd.)Multiple Qualifications (contd.)

01 VENDOR-SSA.* 05 FILLER PIC X(9) VALUE ‘INVENSEG(’. 05 FILLER PIC X(10) VALUE ‘INVENCOD>=’. 05 VENDOR-SSA-LOW-CODE PIC X(3). 05 FILLER PIC X VALUE ‘&’. 05 FILLER PIC X(10) VALUE ‘INVENCOD<=’. 05 VENDOR-SSA-HIGH-CODE PIC X(3). 05 FILLER PIC X 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 the vendor code field must be less than or equal to a particular value; that is the high end of the range

To retrieve segments that fall within this range, you would first move values for low and high ends of the range to VENDOR-SSA-LOW-CODE and VENDOR-SSA-HIGH-CODE

Then you would execute GN calls that include VENDOR-SSA

Page : 55/128

Module 5Module 5Retrieving Data from a Data Retrieving Data from a Data

BaseBase

The GU Call

The GN Call

The GNP Call

Status Codes Expected during Sequential Processing

Using Command Codes with Retrieval Calls

Multiple Processing

Page : 56/128

The GU CallThe GU Call

Used for random processing

Applications of random processingWhen 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-GUINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTVENDOR-SSAITEM-SSASTOCK-LOCATION-SSA.

A typical GU call like the one above, wherein a complete set of qualified SSAs to retrieve a segment, includes one for each level in the hierarchical path to the segment you want to retrieve is called a ‘fully qualified call’

Page : 57/128

The GU Call (contd.)The GU Call (contd.)

Usually, GU processing is based on sequence (key) fields with unique valuesHowever, for some applications you may find it necessary to either

Access a segment whose sequence field allows non-unique valuesAccess a segment based on a field that is not the segment’s key fieldIn 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

3. If you omit some SSAs for intermediate levels in a hierarchical path, the action DL/I takes depends on your current position and on the SSAs that are missing

DL/I either uses the established position or defaults to an unqualified SSA for the segment

Recommended style of codingCode a qualified or unqualified SSA for each level in the path from the root segment to the segment you want to retrieve

Page : 58/128

The GU Call (contd.)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

Page : 59/128

The GN CallThe GN Call

CALL ‘CBLTDLI’ USING DLI-GNINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTSTOCK-LOCATION-SSA.

Used for basic sequential processingAfter any successful data base call, your data base position is immediately before the next segment occurrence in the normal hierarchical sequenceBefore your program issues any calls, position is before the root segment of the first data base recordThe GN call moves forward through the data base from the position established by the previous callIf 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 sequenceIf a GN call includes SSAs– qualified or unqualified– DL/I retrieves only segments that meet requirements of all SSAs you specifyIf 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 callBut when you specify a qualified SSA, DL/I selects only those segment occurrences that meet the criteria you specify

Page : 60/128

The GNP CallThe GNP Call

CALL ‘CBLTDLI’ USING DLI-GNPINVENTORY-PCB-MASKINVENTORY-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

Page : 61/128

The GNP Call (contd.)The GNP Call (contd.)

Established Parent

Vendor 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Established

ParentVendor 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1Fig 5.1 Sequential retrieval with GNP call

Page : 62/128

Status Codes you can expect duringStatus Codes you can expect duringSequential ProcessingSequential Processing

Page : 63/128

Using Command Codes with Using Command Codes with Retrieval CallsRetrieval Calls

The F command codeWhen 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 qualificationsCan 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 callsMeaningless with GU calls, because GU normally retrieves the first segment occurrence that meets the criteria you specify

The L command codeWhen you issue a call with an SSA that includes the L command code, the call processes the last occurrence of the segment named by the SSA, subject to the call’s other qualifications

The D command codeUsed to retrieve more than one segment occurrence using just one callNormally DL/I operates on the lowest level segment you specify in an SSA, but in many cases, you want data not just from the lowest level in the call, but from other levels as wellMakes it easy to retrieve an entire path of segments

Page : 64/128

Using Command Codes with Using Command Codes with Retrieval CallsRetrieval Calls

(contd.)(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-GUINVENTORY-PCB-MASKPATH-CALL-I-O-AREAVENDOR-SSAITEM-SSA

LOCATION-SSA.

Page : 65/128

Using Command Codes with Using Command Codes with Retrieval CallsRetrieval Calls

(contd.)(contd.)

The C command codeIf 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 pathInstead you can use a single SSA with the C command codeThen, rather than coding a field name, relational operator, and search value, you specify the concatenated key for the segment you are interested inAn illustration of the use of the C command code is shown below

* 01 LOCATION-SSA.*

05 FILLER PIC X(11) VALUE ‘INLOCSEG*C(‘. 05 LOCATION-SSA-VENDOR PIC X(3). 05 LOCATION-SSA-ITEM PIC X(5). 05 LOCATION-SSA-LOCATION PIC X(3). 05 FILLER PIC X VALUE ‘)’.

* . . .

CALL ‘CBLTDLI’ USING DLI-GUINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTLOCATION-SSA.

Page : 66/128

Using Command Codes with Using Command Codes with Retrieval CallsRetrieval Calls

(contd.)(contd.)

The P command codeWhen 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 codeWhen 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 dependents of the segments with the U command code

Has the same effect as a call which contains a qualified SSA for the current position

Is ignored if used with a qualified SSA

The V command codeEffect is same as coding the U command code at that level and all levels above it in the hierarchy

Is ignored if used with a qualified SSA

Page : 67/128

Using Command Codes with Using Command Codes with Retrieval CallsRetrieval Calls

(contd.)(contd.)

The Q command codeThis 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

Page : 68/128

Multiple ProcessingMultiple 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 PCBsThe 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 in the ENTRY statement

It is up to the program’s logic to decide when to use a particular PCB to access the data base

This method for implementing multiple processing, though flexible, is inefficient because of the overhead imposed by the extra PCBs

Page : 69/128

Multiple Processing (contd.)Multiple Processing (contd.)

Multiple positioningLets 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 hierarchical path the program processes

Most of the time, multiple positioning is used to access segments of two or more types sequentially at the same time

Fig 5.2 Two data base records to illustrate multiple positioning

A1

B13

B12

B11

Data base Record 1

C13

C12

C11

A2

B22

B21

Data base Record 2

C22

C21

Page : 70/128

Multiple Processing (contd.)Multiple Processing (contd.)

MOVE ‘SEGB ’ TO UNQUAL-SSA-SEGMENT-NAME.CALL ‘CBLTDLI’ USING DLI-GN

SAMPLE-DB-PCBSEGMENT-B-I-O-AREAUNQUALIFIED-SSA.

 MOVE ‘SEGC ’ TO UNQUAL-SSA-SEGMENT-NAME.CALL ‘CBLTDLI’ USING DLI-GN

SAMPLE-DB-PCBSEGMENT-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

It is the DBA who decides whether single or multiple positioning will be in effect in the program’s PSB

As a result multiple positioning is not the characteristic of the data base but instead, it’s how DL/I allows a program to view a data base

The same program can be processed with either single or multiple positioning by different programs

The technique a program uses is determined by the program’s PSB

Page : 71/128

Module 6Module 6Adding and Updating DataAdding and Updating Data

to a Data Baseto a Data Base

The ISRT Call

The Get Hold Calls

The REPL Call

The DLET Call

Common IMS Status Codes

IMS Abends

Sample IMS Program

Page : 72/128

The ISRT CallThe 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-ISRTINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTUNQUALIFIED-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

Page : 73/128

The ISRT Call (contd.)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-ISRTINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTVENDOR-SSAITEM-SSAUNQUALIFIED-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

Page : 74/128

The ISRT Call (contd.)The ISRT Call (contd.)

Where inserted segments are storedIf 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 rule determines how the new segment is positioned relative to existing twin segments

If the rule is “first”, the new segment is added before any existing twins

If the rule is “last”, the new segment is added after all existing twins

If the rule is “here”, it is added at the current position relative to existing twins, which may be first, last, or anywhere in the middle

For a segment with non-unique sequence fields, the rules are similar, but they determine where the new segment is positioned relative to existing twin segments that have the same key value

Page : 75/128

The ISRT Call (contd.)The ISRT Call (contd.)

Status codes you can expect during insert processingGE 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

Page : 76/128

The Get Hold CallsThe 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

Page : 77/128

The REPL CallThe 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-GHUINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTVENDOR-SSAITEM-SSALOCATION-SSA.

ADD TRANS-RECEIPT-QTY TO ISLS-QUANTITY-ON-HAND.SUBTRACT TRANS-RECEIPT-QTY FROM ISLS-QUANTITY-ON-ORDER.CALL ‘CBLTDLI’ USING DLI-REPL

INVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENT.

Page : 78/128

The REPL Call (contd.)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

Page : 79/128

The DLET CallThe DLET Call

The DLET call works much like REPLYou must first issue a get hold call to indicate that you intend to make a change to the segment you are retrievingThen you issue a DLET call to delete the segment occurrence from the data baseFor 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 DLI-GHUINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENTVENDOR-SSAITEM-SSALOCATION-SSA.

CALL ‘CBLTDLI’ USING DLI-DLETINVENTORY-PCB-MASKINVENTORY-STOCK-LOC-SEGMENT.

Notice that the DLET call does not include any SSAsThere 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 itThe status codes you might get after a DLET call are the same as those you can get after an REPL call

Page : 80/128

Common IMS Status CodesCommon IMS Status Codes

Returned by IMS after each DB callField STATUS-CODE X(02) in the PCB-MASK definitionAcceptable 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, GBAK – Invalid field name in SSA

ISRT – AB, AC, AD, AJ, AK, IIAC – Segment not foundAD – Wrong PCB used II -- Segment occurrence already exists in the DB

REPL -- AB, AC, AD, DJ

DLET – AB, AJ, DJAB – I/O area not specified in the callAJ – Invalid SSA format (invalid command code etc)DJ – Segment not in ‘HOLD’ status

Page : 81/128

IMS AbendsIMS 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

Page : 82/128

Sample IMS ProgramSample 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 PIC X VALUE '1'. 77 GET-UNIQUE PIC X(4) VALUE 'GU'.

01 HOSPITAL-SSA. 05 FILLER PIC X(19) VALUE 'HOSPITAL(HOSPNAME ='. 05 HOSPNAME-SSA PIC X(20). 05 FILLER PIC X VALUE ')'. 01 WARD-SSA. 05 FILLER PIC X(19) VALUE 'WARD (WARDNO ='. 05 WARDNO-SSA PIC X(04). 05 FILLER PIC X VALUE ')'. 01 PATIENT-SSA. 05 FILLER PIC X(19) VALUE 'PATIENT (PATNAME ='. 05 PATNAME-SS PIC X(20). 05 FILLER PIC X VALUE ')'. 01 UNQUAL-HOSPITAL-SSA PIC X(9) VALUE 'HOSPITAL '. 01 UNQUAL-WARD-SSA PIC X(9) VALUE 'WARD '. 01 UNQUAL-PATIENT-SSA PIC X(9) VALUE 'PATIENT '.

01 WS-ISRT PIC X(4) VALUE 'ISRT'. 01 WS-GHU PIC X(4) VALUE 'GHU '. 01 HOSP-I-O-AREA. 05 HOSP-NAME PIC X(20). 05 HOSP-ADDRESS PIC X(30). 05 HOSP-PHONE PIC X(10).

01 WARD-I-O-AREA. 03 WARD-NO PIC X(04). 03 TOT-ROOMS PIC 9(03). 03 TOT-BEDS PIC XXX. 03 BEDAVAIL PIC X(3). 03 WARD-TYPE PIC X(20).

Page : 83/128

Sample Program (contd.)Sample Program (contd.)

01 PATIENT-I-O-AREA. 03 PATIENT-NAME PIC X(20). 03 PATIENT-ADDRESS PIC X(30). 03 PATIENT-PHONE PIC X(10). 03 BEDINDENT PIC X(4). 03 DATEADMT PIC X(8). 03 PREV-STAY-FLAG PIC X. LINKAGE SECTION. 01 PCB-MASK. 02 DBD-NAME-1 PIC X(8). 02 SEG-LEVEL-1 PIC XX. 02 STATUS-CODE-1 PIC XX. 02 PROCESS-OPTIONS-1 PIC X(4). 02 KEY-LENGTH PIC S9(5) COMP. 02 SEG-NAME-FDBK-1 PIC X(8). 02 LENGTH-FB-KEY-1 PIC S9(5) COMP. 02 NUMB-SENS-SEGS-1 PIC S9(5) COMP. 02 KEY-FB-AREA-1 PIC 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.

Page : 84/128

Sample Program (contd.)Sample Program (contd.)

IF STATUS-CODE-1 NOT EQUAL SPACES EXIT.INSERT-HOSP-EXIT.

EXIT.INSERT-WARD-01-PARA. MOVE '01' TO WARD-NO. MOVE 10 TO TOT-ROOMS. MOVE 20 TO TOT-BEDS. MOVE '03' TO BEDAVAIL MOVE 'INTENSIVE' TO WARD-TYPE. CALL 'CBLTDLI' USING WS-ISRT 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' TO WARDNO-SSA. MOVE 'JOHN SMITH' TO PATIENT-NAME. MOVE '123 HAMILTON STR' TO PATIENT-ADDRESS. MOVE '12345 ' TO PATIENT-PHONE. MOVE '1111' TO BEDINDENT. MOVE '02021999' TO DATEADMT. MOVE 'N' TO PREV-STAY-FLAG. CALL 'CBLTDLI' USING WS-ISRT PCB-MASK PATIENT-I-O-AREA

HOSPITAL-SSA WARD-SSA

UNQUAL-PATIENT-SSA.

IF STATUS-CODE-1 NOT EQUAL SPACES EXIT. INSERT-PATIENTS-EXIT.EXIT.

Page : 85/128

Module 7Module 7Secondary IndexingSecondary 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

Page : 86/128

The Need for Secondary IndexingThe 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

Page : 87/128

A Customer Data BaseA Customer Data Base

Customer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Fig 7.1 The customer data base

Page : 88/128

The Customer Data Base (contd.)The Customer Data Base (contd.)

01 CUSTOMER-SEGMENT. 05 CS-CUSTOMER-NUMBER PIC X(6). 05 CS-CUSTOMER-NAME PIC X(31). 05 CS-ADDRESS-LINE-1 PIC X(31). 05 CS-ADDRESS-LINE-2 PIC X(31). 05 CS-CITY PIC X(18). 05 CS-STATE PIC XX. 05 CS-ZIP-CODE PIC X(9).* 01 SHIP-TO-SEGMENT. 05 STS-SHIP-TO-SEQUENCE PIC XX. 05 STS-SHIP-TO-NAME PIC X(31). 05 STS-ADDRESS-LINE-1 PIC X(31). 05 STS-ADDRESS-LINE-2 PIC X(31). 05 STS-CITY PIC X(18). 05 STS-STATE PIC XX. 05 STS-ZIP-CODE PIC X(9).* 01 BUYER-SEGMENT. 05 BS-BUYER-NAME PIC X(31). 05 BS-TITLE PIC X(31). 05 BS-TELEPHONE PIC X(10).* 01 RECEIVABLE-SEGMENT. 05 RS-INVOICE-NUMBER PIC X(6). 05 RS-INVOICE-DATE PIC X(6). 05 RS-PO-NUMBER PIC X(25). 05 RS-PRODUCT-TOTAL PIC S9(5)V99COMP-3. 05 RS-CASH-DISCOUNT PIC S9(5)V99COMP-3. 05 RS-SALES-TAX PIC S9(5)V99COMP-3. 05 RS-FREIGHT PIC S9(5)V99COMP-3. 05 RS-BALANCE-DUE PIC S9(5)V99COMP-3.*

Fig 7.2 Segment Layouts for the Customer Data Base (Part 1 of 2)

Page : 89/128

The Customer Data Base (contd.)The Customer Data Base (contd.)

01 PAYMENT-SEGMENT. 05 PS-CHECK-NUMBER PIC X(16). 05 PS-BANK-NUMBER PIC X(25). 05 PS-PAYMENT-DATE PIC X(6). 05 PS-PAYMENT-AMOUNT PIC S9(5)V99 COMP-3.* 01 ADJUSTMENT-SEGMENT. 05 AS-REFERENCE-NUMBER PIC X(16). 05 AS-ADJUSTMENT-DATE PIC X(6). 05 AS-ADJUSTMENT-TYPE PIC X. 05 AS-ADJUSTMENT-AMOUNT PIC S9(5)V99 COMP-3.* 01 LINE-ITEM-SEGMENT. 05 LIS-ITEM-KEY. 10 LIS-ITEM-KEY-VENDOR PIC X(3). 10 LIS-ITEM-KEY-NUMBER PIC X(3). 05 LIS-UNIT-PRICE PIC S9(5)V99 COMP-

3. 05 LIS-QUANTITY PIC S9(7) COMP-

3.*

Fig 7.2 Segment Layouts for the Customer Data Base (Part 2 of 2)

Page : 90/128

Secondary IndexesSecondary Indexes

Customer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Prefix Data

Rec. Seg. Addr.

InvoiceNo.

IndexPointerSegment

Invoice number index data base

Secondary IndexData Base

Customer Data Base

Indexed Data Base

Index TargetSegment

Index SourceSegment

Fig 7.3 Secondary Indexing Example in which the Index Source Segment and the Index Target Segment are the same

Page : 91/128

Secondary Indexes (contd.)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 updates the index

That can also result in performance degradation

Page : 92/128

Secondary Indexes (contd.)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

Page : 93/128

Secondary KeysSecondary 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

Page : 94/128

Secondary Data StructuresSecondary 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

Customer

Receivable

Ship-to Payment Adjustment Line Item

Buyer

Fig 7.4 Secondary Data Structure for the Secondary Index

Page : 95/128

Secondary Data Structures (contd.)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

Page : 96/128

DBDGEN Requirements forDBDGEN Requirements forSecondary IndexesSecondary Indexes

Because a secondary index relationship involves two data bases, two DBDGENs are 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

Page : 97/128

DBDGEN Requirements forDBDGEN Requirements forSecondary Indexes (contd.)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

Page : 98/128

DBDGEN Requirements forDBDGEN Requirements forSecondary Indexes (contd.)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

Page : 99/128

PSBGEN Requirements forPSBGEN Requirements forSecondary IndexingSecondary Indexing

Just because a secondary index exists for a data base doesn’t mean DL/I will 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

Page : 100/128

PSBGEN Requirements forPSBGEN Requirements forSecondary Indexing (contd.)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

Page : 101/128

Indexing a SegmentIndexing a Segmentbased on a Dependent Segmentbased on a Dependent Segment

Fig 7.8 Secondary Indexing Example in which the Index Source Segment and the Index Target Segment are different

Customer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Prefix Data

Cust. Seg. Addr.

ItemNo.

IndexPointerSegment

Invoice number index data base

Secondary Index Data Base

Customer Data Base

Indexed Data Base

Index TargetSegment

Index SourceSegment

Page : 102/128

Indexing a SegmentIndexing a Segmentbased on a Dependent Segment based on a Dependent Segment

(contd.)(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 be possible to index the buyer segment based on values in the line item segment, because the line item segment isn’t dependent on the buyer segment

Similarly , you couldn’t index the line item segment based on the customer segment, because the customer segment is superior to the line item segment

Page : 103/128

The Independent AND OperatorThe 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 PIC X(9) VALUE ‘CRCUSSEG(’. 05 FILLER PIC X(10) VALUE ‘CRLINXNO =’. 05 SSA-ITEM-KEY-1 PIC X(8). 05 FILLER PIC X VALUE ‘#’. 05 FILLER PIC X(10) VALUE ‘CRLINXNO =’. 05 SSA-ITEM-KEY-2 PIC X(8). 05 FILLER PIC X VALUE ‘)’.

Page : 104/128

Sparse SequencingSparse 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 indexSparse sequencing can improve performance when some occurrences of the index source segment must be indexed but others need not beDL/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 segmentThe suppression routine is a user-written program that evaluates the segment and determines whether or not it should be indexedNote:

When sparse indexing is used, its functions are handled by DL/IYou don’t need to make special provisions for it in your application program

Page : 105/128

Duplicate Data FieldsDuplicate 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

Page : 106/128

Module 8Module 8Logical Data BasesLogical Data Bases

Introduction to Logical Data Bases

Logical Data Base Terminology

DBDGENs for Logical Data Bases

Page : 107/128

An Introduction to Logical Data An Introduction to Logical Data BasesBases

Inter related databases.Inter related databases

A logical child segment has 2 parent segments

One physical parent and one logical parent

DB1

DB2

Logical Parent

Physical Parent

Logical relationship

Virtual Logical Child

C2

SEG-1

LP

VLC

Real Logical Child

SEG-a SEG-b RLC

PP

Page : 108/128

Logical Data Base TerminologyLogical Data Base Terminology

Real Logical ChildThe child under consideration

Physical ParentOriginal parent of the child

Logical ParentThe parent in the other data base

Virtual Logical ChildThe child as seen from the other data base

Three types of Logical data basesUnidirectional.

The child accesses logical parent’s data but the reverse is not allowed.

Bi-directional virtual.Accesses in both the directions, but the child exists only in the physical DB.

Bi-directional physical.Accesses in both the directions, but the child exists both in the physical DB as well as the logical DB.

Page : 109/128

DBDGENs for a Logical Data BaseDBDGENs 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=********************************

Page : 110/128

Module 9Module 9Recovery and RestartRecovery and Restart

Introduction to Data Base Recovery

Introduction to Checkpointing

Types of Checkpointing

Extended Restart

Database Image Copy

Page : 111/128

Introduction to Data Base RecoveryIntroduction 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 recoveriesForward recovery

Backward recovery

Forward RecoveryData 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 forward recovery

Used when a data base is physically damaged

Backward RecoveryData base changes due to the failed program is reverted directly in the data base

Program log records are read backwards and their effects are reversed in the data base

When back out is complete data base is in the former state that was before the failure

Normally applied when the program ends in a controlled fashion and no data base damage

Page : 112/128

Introduction to CheckpointingIntroduction 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

Page : 113/128

Types of CheckpointingTypes of Checkpointing

Types of checkpointingBasic checkpointing

Symbolic checkpointing

Basic checkpointingSimple form of checkpointing.

Issues checkpoint calls that the DL/I recovery utilities use during recovery processing

Symbolic checkpointingMore advanced type of checkpointing

Used in combination with extended restart

Programs resume from the point following the checkpoint, in case of a failure

Store program data and CHKP records and retrieve them at the time of restart

Along with symbolic CHKP call you must use the XRST (Extended Restart) call too.

Page : 114/128

Extended Restart (XRST)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 waysIn the I/O area pointed to by the XRST call

Specifying ID in the CKPTID= field of EXEC statement in the program's JCL

Page : 115/128

Database Image CopyDatabase 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

Advantage :

Simple, Fast, Automated procedure

Page : 116/128

Module 10Module 10 DL/I Data Base Organizations DL/I Data Base Organizations

DL/I Organizations & Access Methods

Hierarchical Sequential Organization

Hierarchical Direct Organization

Additional IMS Access Methods

Page : 117/128

DL/I Organizations & Access DL/I Organizations & Access MethodsMethods

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.

Page : 118/128

Hierarchic Sequential Organizations Hierarchic Sequential Organizations Access MethodsAccess 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 Method):Similar to HSAM but used to support databases that consist only of root segments.

SHISAM(Simple Hierarchic Indexed Sequential Access Method ) : Similar to HISAM and used in cases in which the database consist of only root segments.

SHSAM & SHISAM are used primarily for converting standard files to DL/I data bases.

Page : 119/128

Hierarchic Direct Organization Hierarchic Direct Organization Access MethodAccess 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.

In HIDAM, unlike HDAM root segment is located through an index.

Root segments can be retrieved in sequence.

Page : 120/128

Additional IMS Access MethodsAdditional 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.

Since files are considered by IMS to be databases, IMS recovery facilities can be used.

Fast Path data bases:Fast Path data bases provide fast processing of simple data structures.

Two types of Fast Path databases : MSDB(Main Storage Data Base ) & DEDB( Data Entry Data Base ).

MSDB(Main Storage Data Base) : It is used to store an application’s most intensively used data and resides in virtual storage.

It provides fast access to data and it contains only a small amount of data.

These are root-segment-only data bases.

Page : 121/128

Additional IMS Access Methods Additional IMS Access Methods (contd..)(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.

Page : 122/128

Module 11Module 11Advanced DL/I featuresAdvanced DL/I features

Variable Length Segments

DBD for GSAMs

PCB for GSAMs

Page : 123/128

Variable Length SegmentsVariable 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 asSEGM 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)

The I-O area should be large enough to accommodate the Maximum variable length segment + Length field

Before an ISRT / REPLACE / DELETE call is issued we have to move the actual length to the length field in the I/O area

Page : 124/128

Variable Length Segments (contd.)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 performance drops

Page : 125/128

DBD for GSAMsDBD 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 belowDBD NAME=CARDS,ACCESS=(GSAM,BSAM)

DATASET D1=ICARDS,DD2=OCARDS,RECFM=F,RECORD=80

DBDGEN

FINISH

END

In GSAM DBD's you can't specifySEGM 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 accommodate the ZZ field.

Page : 126/128

DBD for GSAMs (contd.)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.

Page : 127/128

PCB for GSAMsPCB 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 belowPCB 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

Page : 128/128

Thank YouThank You