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IMS DB

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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.

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Prerequisites

Knowledge of COBOL

Basic knowledge of data base management concepts

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Course 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 Base6. Adding and Updating Data to a Data Base

7. Secondary Indexing

8. Logical Data Bases

9. Recovery and Restart

10. DL/I Data Base Organizations11. Advanced DL/I features

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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

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Module 1

An Introduction to DL/I Data

BasesHierarchical StructuresWhy a Data Base Management System

Basic DL/I TerminologyBasic DL/I Data Base Processing

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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 hierarch ical struc ture

DL/I sup po rts hierarchies that are dif f icu l t to implement w ith standard f i les.

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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

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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

ADDRESS

House

Number

Street

Name

City State Country Zip Code

Fig 1.3 The ADDRESS segment w ith six fields

Segment Type

A category of data

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

Segment Occurrence

One speci f ic segment o f a particu lar type contain ing user data

Note:-

Within a data base there is only one of each segment type- its part of the data bases definition-

but there can be an unl imited number of occ urrences 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 con text

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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 Locat ion

Fig 1.4 The hierarchical structu re of the Inventory

data base with three segment types

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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 thesegment 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 subordinatesegment occurrences

Data base

Record 1

Data base Record

2

Vendo r 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Vendo r 2

Item 1

Loc 2

Loc 1

Fig 1.6 Two data base records from the Inventory data base

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Dependent Segment

A segment other than the root segment in a data

base record

Accessible only through one or more parentsegments

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

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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

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Basic DL/I Terminology (contd.) Logical data bases

Additional 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 Locat ion

Item

Vendor

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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

Data base

Record 1

Data base Record 2

Vendo r 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 proc essing

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Basic DL/I Data Base Processing

(contd.) Random (Direct) Processing Key (sequence) field required

Concatenated Key Completely 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

Vendo r 1

Item 1

Item 2

Loc 5Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Vendor 2

Item 1

Loc 2

Loc 1

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Module 2

DL/I Programs and Control BlocksThe IMS Software Environment

How DL/I relates to your application programs

Control Blocks

DBDGEN

PSBGENIMS Processing Options

ACB & ACBGEN

Running an application program under DL/I

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The IMS Software EnvironmentAppl icat ion

Programs

IMS Contr ol

B locks

DL/I

OS

Data Base

IMS DC Remote

Terminal

Fig 2.1 The IMS Software Envir onm ent

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How DL/I relates to

your application programsAppl icat ion

Program

Operating System

Access Method

(eg. VSAM)

File

Data Set

Standard File Process ing

Appl icat ion

Program

DL/I Data Base Processing

DL/I

Operating Sys tem

Access Method

(eg. VSAM)

Data Base

Data SetFig 2.2 Standard fi le proc essing c ompared to DL/I data base proc essing

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How DL/I relates

to your application programs (contd.) Standard file processing

Standard COBOL statements (like READ / WRITE) invoke theappropriate access method (like VSAM)

Format of the record as processed by the program should be the sameas 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 database data on disk

Format of records in a data base data set need not match the layoutsof the segments that make up the data base

The way the program sees the data base is different from the way theaccess method sees it.

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Control Blocks Physical structure of a DL/I data base isnt specified in an application program

DL/I uses a set of control blocks(DBDs and PSBs) to define a data bases 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 programs 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 baseprocessing requirements can share a PSB

Data Base Administrator (DBA) has to create DL/I control blocks

DBDGEN and PSBGEN Control Statements

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slide)STMT SOURCE STATEMENT1 PRINT NOGEN

2 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

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SAMPLE DBDGEN (contd.)

Explanation of Fig 2.3

First macroDBDidentifies the data base and specifies theDL/I access method

Second macroDATASET- identifies the file that would containthe data base

Symbolic name (IN) identifies the data set in the JCL atexecution time

Segment types are defined using the SEGM macro

Segment hierarchical relationships are specified by the PARENTparameter on a SEGM macro

PARENT= 0 or absence of PARENT parameter specifies root segment

POINTER parameter and LCHILD macro are needed for HIDAMDatabases

Only search fields need be specified in the DB

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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 decim al

Z Zoned decim al

X Hexadecimal

H Half word Binary

F Ful l word Binary

SEQ parameter specif ies a sequenc e fieldsegment oc currences are added in sequence by v alues in these f ields

Fig 2.4 FIELD macro TYPE parameter codes

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SAMPLE PSBGENSTMT SOURCE STATEMENT1 PRINT NOGEN2 PCB TYPE=DB,DBDNAME=INDBD,PROCOPT=LS

3 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 programs PSBGEN

Explanation of Fig 2.5

PCB (Program Communication Block) refers to one database.

One PCB macro for each database accessed

Segment Level Sensitivity A programs 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

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PSBGEN (contd.)

DBDNAME parameter on the PCB macro specifies the name ofthe DBD

KEYLEN parameter specifies the length of the longestconcatenated key the program can process in the data base

PROCOPT parameter specifies the programs processing options

For each PCB macro, subordinate SENSEG macros identify thesensitive segments in the data base

Names specified in the SENSEG macros must be segment namesfrom the DBDGEN for the data base named in the DBDNAMEparameter 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 bewritten.

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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 theload

The PROCOPT given for a Sensitive segment would override the one given forthe 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 !

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ACB & ACBGEN

ACB(Application Control Blocks) : It is created by merging and expanding PSBs and

DBDs 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 ACBs either dynamically or it can prebuild them using ACBmaintenance utility.

ACBs cannot be prebuilt for GSAM DBDs.

ACBs can be prebuild for PSBs that reference GSAM databases.

ACBs save instruction, execution and direct-access wait time and improves

performance in application scheduling. ACBs are maintained in IMS.ACBLIB library.

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Running an application program under

DL/I Batch program does not access IMS directly

JCL invokes the DL/I batch initialization module DFSRRC00 which loadsthe application program and the required DL/I modules

The program and DL/I modules execute together

Sample JCL :

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//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'

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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=*

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Module 3

COBOL Basics for Processing a

DL/I Data BaseThe ENTRY and GO BACK Statements

The DL/I Call

The PCB Mask

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ENTRY and

GO BACK StatementsENTRY 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 programs 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 ENTRYstatement

PCB masks should be listed on the ENTRY statement in the same sequence as they appear in

your programs 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

Use GO BACK and not a STOP RUN statement

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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-functionPCB-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 yourprograms object module

PLITDLI, ASMTDLI are other options

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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 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 .

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Get functions First six 05-level items in Fig 3.3

Used to retrieve segments from a DL/I data base

GUget unique function causes DL/I to retrieve a specific segment

occurrence based on field values that you specify GNget next function used to retrieve segment occurrences in

sequence

GNPget 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

U date functions

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Other functions Functions CHKP (the checkpoint function) and XRST (the restart

function) are used in programs to take advantage of IMSs 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)

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PCB mask

Second parameter on the DL/I call

The name of the PCB mask defined in the

programs Linkage Section ENTRY statement establishes a correspondence

between PCB masks in the Linkage Section and

the PCBs within the programs 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 arameter on the DL I call

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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 SSAsunqualified 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

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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 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

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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

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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 programs view of the

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Module 4

Segment Search ArgumentsTypes of SSAs

Basic Unqualified SSA

Basic Qualified SSA

Command Codes

The Null Command Code

Path Call

Multiple Qualifications

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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

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Basic 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

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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

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Basic 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

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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

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Command Codes

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

Fig 4.3 Unqual i fied SSA format with a single command code

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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 FILLER PIC X VALUE *.

05 UNQUAL-SSA-COMMAND-CODE PIC X.

05 FILLER PIC X VALUE SPACE.

*

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Command Codes (contd.)Command Code Meaning

C Concatenated Key

D Path Call

F First Occurr ence

L Last Occurrence

N Path Call Ignore

P Set Parentage

Q Enqueue Segment

U Maintain pos it ion at this level

V Maintain pos it ion at this and all

super ior levels

Nul l comm and code

Fig 4.5 SSA Comm and Codes

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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 FILLER PIC X VALUE *.

05 UNQUAL-SSA-COMMAND-CODE PIC X VALUE -.

05 FILLER PIC X VALUE SPACE.*

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Path Call

A DB call with an SSA that includes the 'D' Command code is a "PATH CALL . Its afacility 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-SSAITEM-SSA

STOCK-LOC-SSA

Normally, DL/I operates on the lowest level segment that is specified in anSSA(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 ofthe 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 specifiedin 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.

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Multiple Qualifications There are two cases in which you would use multiple qualification

When you want to process a segment based on thecontents of two or more fields within it

When you want to process a segment based on arange of possible values for a single field

To use multiple qualification, you connect two or more qualification statements (a fieldname, a relational operator, and a comparison value) within the parentheses of theSSA.

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 indexesand will be discussed later

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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

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Module 5

Retrieving Data from a Data BaseThe GU Call

The GN Call

The GNP Call

Status Codes Expected during Sequential Processing

Using Command Codes with Retrieval Calls

Multiple Processing

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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.

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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 non-unique values

Access a segment based on a field that is not thesegments key field

In the above cases, DL/I returns the first segmentoccurrence 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/Iaccesses the first segment occurrence in the database that meets the criteria you specify

2.If you issue a GU call without any SSAs, DL/I returnsthe first occurrence of the root segment in the database

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The GU Call (contd.)

Status codes you can expect during random processing with GU calls

Only two status code values need to be

consideredspaces and GE

Spaces means the call was successful and therequested segment was returned in your

programs segment I/O area

A GE status code indicates that DL/I couldnt find a

segment that met the criteria you specified in thecall

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The GN Call

CALL CBLTDLI USING DLI-GNINVENTORY-PCB-MASK


STOCK-LOCATION-SSA.

Used for basic sequential processing

After any successful data base call, your data base position is immediately beforethe next segment occurrence in the normal hierarchical sequence

Before your program issues any calls, position is before the root segment of thefirst data base record

The GN call moves forward through the data base from the position established bythe previous call

If a GN call is unqualified (that is, if it does not employ an SSA), it returns the nextsegment occurrence in the data base regardless of type, in hierarchical sequence

If a GN call includes SSAsqualified or unqualifiedDL/I retrieves only segmentsthat 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 occurrencesthat meet the criteria ou s ecif

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The GNP Call

CALL CBLTDLI USING DLI-GNPINVENTORY-PCB-MASK


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 returnsGE as the status code

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The GNP Call (contd.)

Established

Parent

Vendo r 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1

Established

ParentVendo r 1

Item 1

Item 2

Loc 5

Loc 4

Loc 3

Loc 2

Loc 1

Loc 2

Loc 1Fig 5.1 Sequential retr ieval with GNP call

Status Codes you can expect during

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Status Codes you can expect during

Sequential Processing

Using Command Codes with

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Using Command Codes with

Retrieval Calls The F command code

When you issue a call with an SSA that includesthe F command code, the call processes the firstoccurrence of the segment named by the SSA,

subject to the calls other qualifications Can be used when you are doing sequential

processing and you need to back up in the database, or in other words, the F command code can

be used for sequential retrieval using GN and GNPcalls

Meaningless with GU calls, because GU normallyretrieves the first segment occurrence that meets

the criteria you specify

Us ng Comman Co es w t

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gRetrieval 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).


*

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).


*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-MASK


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gRetrieval Calls

(contd.) The C command code

If you are developing a program that retrieves justlower-level segment occurrences from a database, you dont 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 theconcatenated key for the segment you areinterested in

An illustration of the use of the C command code

is shown below


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gRetrieval 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


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gRetrieval 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 andthe time you are finished with it

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Multiple Processing

Multiple processing is a general term that means a program can have more thanone 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

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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

hierarchical path the program processes

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

the same time

Fig 5.2 Two d ata base records to il lustrate mult iple po sit ion ing

A1

B13B12

B11

Data base Record 1

C13C12

C11

A2

B22

B21

Data base

Record 2

C22

C21

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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

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Module 6

Adding and Updating Data

to a Data BaseThe ISRT Call

The Get Hold CallsThe REPL Call

The DLET Call

Common IMS Status Codes

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The ISRT Call

The ISRT call is used to add a segment occurrence to a data base, either duringupdate 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: anunqualified SSA for the segment type you want to add

Consider the example below

CALL CBLTDLI USING DLI-ISRT

INVENTORY-PCB-MASK

INVENTORY-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

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The ISRT Call (contd.)

A safer technique is to specify a qualified SSA for each hierarchical level above theone where you want to insert the segment, as illustrated below

CALL CBLTDLI USING DLI-ISRT

INVENTORY-PCB-MASK


VENDOR-SSAITEM-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 isnt 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

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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 dont have sequence fields at all

When thats the case, where the segmentoccurrence 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 se ment is

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Status codes you can expect during insert processing

GEWhen you use multiple SSAs and DL/I

cannot satisfy the call with the specified path

I IWhen 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 exacthierarchical sequence

That means there is an error in your program or the files from which you

are loading the data base contain incorrect data

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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

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The REPL Call

After you have retrieved a segment with one of the get hold calls, you can makechanges 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 cant change the length of the segment

2.You cant 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 belowCALL CBLTDLI USING DLI-GHU

INVENTORY-PCB-MASK


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

h ll ( d )

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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 segments

key field before issuing the REPL call, DL/I returnsa DA status code

h ll

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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, youd code a seriesof statements like the ones below

CALL CBLTDLI USING DLI-GHUINVENTORY-PCB-MASK


VENDOR-SSA

ITEM-SSA

LOCATION-SSA.

CALL CBLTDLI USING 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 DLETcallwhen you delete a segment, you automatically delete all segmentoccurrences subordinate to it

The status codes you might get after a DLET call are the same as those you can get

C S S C d

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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, GUAB, AK, GE, GB

AKInvalid field name in SSA

ISRTAB, AC, AD, AJ, AK, II

ACSegment not found

IMS Ab d

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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 IMScheck the job log for IMS return code

Check the JCLif 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

S l IMS P

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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 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).


01 PATIENT-SSA.

05 FILLER PIC X(19) VALUE 'PATIENT (PATNAME ='.

05 PATNAME-SS PIC X(20).


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).

S l P ( d )

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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.

S l P ( td )

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Sample Program (contd.)

IF STATUS-CODE-1 NOT EQUAL SPACESEXIT.

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.


PCB-MASKWARD-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.


PCB-MASK

PATIENT-I-O-AREA

HOSPITAL-SSA

WARD-SSA

UNQUAL-PATIENT-SSA.

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Module 7

Secondary Indexing

The Need for Secondary Indexing

A Customer Data Base

Secondary Indexes

Secondary Keys

Secondary Data Structures

DBDGEN Requirements for Secondary IndexesPSBGEN Requirements for Secondary Indexing

Indexing a Segment based on a Dependent Segment

The Independent AND Operator

Sparse Sequencing

Duplicate Data Fields

Th N d f S d I d i

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The Need for Secondary Indexing

Often you need to be able to access a data base in an order other than its primaryhierarchical 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 C t D t B

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A Customer Data BaseCustomer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Fig 7.1 The customer data base

Th C t D t B ( td )

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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)V99 COMP-3.

- - -

Th C t D t B ( td )

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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)

S d I d

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Secondary IndexesCustomer

Ship-to

Buyer Receivable


Prefix Data

Rec. Seg.

Addr.

Invoice

No.

Index

PointerSegment

Invoice number index data base

Secondary Index

Data BaseCustomer Data Base

Indexed Data Base

Index Target

SegmentIndex Source

Segment

Fig 7.3 Secon dary Indexin g Examp le in which t he Index Sour ce Segment and the Index Target Segment are the same

Secondary Indexes (contd )

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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 pointersegment

The index pointer segment contains two main elementsa 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

segmentthe 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 basethough 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 )

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Secondary Indexes (contd.)

If multiple access paths are required into the same data base, the DBA can defineas many different secondary indexes as necessaryeach 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

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Secondary Keys

The field in the index source segment over which the secondary index is built iscalled the secondary key

The secondary key need not be the segments sequence fieldany 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

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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 isnt 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 Second ary Index

Secondary Data Structures (contd )

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Secondary Data Structures (contd.)

Secondary data structures dont change the way the data base segments arestored 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 secondaryindex, you must consider how the secondary data structure affects your programs

logic

DBDGEN Requirements for

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Secondary Indexes Because a secondary index relationship involves two data bases, two DBDGENs arerequiredone for the indexed data base and the other for the secondary index data

base

Fig 7.5 Part ial DBDGEN outpu t for the custom er data base showing the code to implem ent the secondary index


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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


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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 fieldCRRECXNO

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

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Secondary Indexing Just because a secondary index exists for a data base doesnt mean DL/I willautomatically 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 processingsequence for the data base on the PROCSEQ parameter of the PSB macro

If it doesnt, 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 Outp ut

PSBGEN Requirements for

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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 programs PSBGEN will contain more than one PCB

macro, each specifying a different value for the PROCSEQ parameter

Indexing a Segment

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based on a Dependent Segment

Fig 7.8 Secondary Indexing Ex ample in which the Index Source Segment and th e Index Target

Segment are different

Customer

Ship-to

Buyer Receivable


Prefix Data

Cust. Seg.Addr.

ItemNo.

IndexPointer

Segment

Invoice number index data base

Secondary Index Data BaseCustomer Data Base

Indexed Data Base

Index Target

Segment

Index Source

Segment

In ex ng a Segmentbased on a Dependent Segment

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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 acustomer 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 wouldnt


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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).


Sparse Sequencing

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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 theindex

Sparse sequencing can improve performance when some occurrences of the indexsource segment must be indexed but others need not be

DL/I uses a suppression value, a suppression routine, or both to determine whether asegment should be indexed (either when inserting a new segment or processing anexisting one)

If the value of the sequence field(s) in the index source segment matches a suppressionvalue specified by the DBA, no index relationship is established (for an insert) orexpected (for any other call)

The DBA can also specify a suppression routine that DL/I invokes to determine the indexstatus for the segment

The suppression routine is a user-written program that evaluates the segment anddetermines whether or not it should be indexed

Note:

When sparse indexing is used, its functions arehandled by DL/I

You dont need to make special provisions for it in


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For some applications, it might be desirable to store user data from the indexsource 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 aseparate data base

Note:

Duplicate data fields impose extra DL/I overhead

and require extra DASD storage

It is the DBAs responsibility to decide whether the

advantages of using duplicate data fields outweigh

the extra DL/I overhead and DASD storage

requirements mentioned above

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Module 8

Logical Data BasesIntroduction to Logical Data Bases

Logical Data Base Terminology

DBDGENs for Logical Data Bases

An Introduction to Logical Data

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Bases

Inter related databases.

Inter related databases

A logica l chi ld s egment has 2 parent segments

One physical parent and on e log ical parent

DB1

DB2

Logic al Parent

Physical

Parent

Virtual

Logical Chi ld

C2

SEG-1

LP

VLC

Real

Logical

Child

SEG-a SEG-b RLC

PP


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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

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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=********************************

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Module 9

Recovery and RestartIntroduction to Data Base Recovery

Introduction to Checkpointing

Types of Checkpointing

Extended Restart

Database Image Copy

Introduction to Data Base Recovery

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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


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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 theprogram

CHKP creates a checkpoint record on DL/I log which prevents recovery before that

point


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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)

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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

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Database Image Copy

Job which is run to take backup copies of IMS database datasets at periodicintervals

Traditionally, batch cycle starts at 7 pm and ends

at 7 am

Image Copy jobs are usually run before and after abatch cycle

If abend occurs, revert to the DB generated by

image copy job and rerun

Commonly used image copy utility is BMC

Softwares ICPUMAIN

Database and Image copy DD names specified in

the ICPSYSIN card

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Module 10

DL/I Data Base OrganizationsDL/I Organizations & Access Methods

Hierarchical Sequential Organization

Hierarchical Direct Organization

Additional IMS Access Methods

DL/I Organizations & Access

h d

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Methods

File Organization is a description of how a file is processed & Access Method is thesoftware 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

h d

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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 deletesegments 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

A M h d

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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


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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.


( d )

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(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.

DEBDs use a complicated storage scheme that

involves separating the data base into as many as

240 areas and this allows very large data bases.

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Module 11

Advanced DL/I featuresVariable Length Segments

DBD for GSAMs

PCB for GSAMs

Variable Length Segments

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g g

When a field length that is stored in a segment type varies, for exampleDescription 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 thevariable 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.)

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g g ( )

Variable Length Segments are appropriate when segment occurrence length varybut once created and made stabilized.

Disadvantage:

If the occurrence of the segment type grows inlength 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

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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 specify

SEGM and FIELD statements

The use of logical or index relationships between

segments IMS adds 2 b tes to the record len th value s ecified in the DBD in order to

DBD for GSAMs (contd.)

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( )

Whenever the database is GSAM/BSAM and the records are variable (V or VB), IMSadds 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

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The PCB for a GSAM database is coded as shown belowPCB 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

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