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IMS DBIMS DBCourse Code:

Version No: 1.1

Date of Release: April 3, 2002

Authors:

Deepak Madhusoodanan

Prasad Krishna Murthy Rajagopa Balakrishnan

Tinu J Punnoor

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ObjectivesObjectives

To create awareness among trainees about the IMS DBtechnology and how it is used to perform data base

operations.

The target audience consists of people who are new or

relatively new to the IMS DB Technology.

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Course OutlineCourse Outline

1. An Introduction to DL/I Data Bases

2. An Introduction to DL/I Programs and Control Blocks

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

4. Using Segment Search Arguments

5. Retrieving Data from a Data Base

6. Adding and Updating Data in a Data Base7. Secondary Indexing

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ReferencesReferences

IMS for the COBOL Programmer Part 1: Data base processing with IMS/VS and DL/I DOS/VS

By Steve Eckols

IBM IMS Primer

By Rick Long, Mark Harrington, Robert Hain, Geoff Nicholls

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

Hierarchical Structures

Why a Data Base Management System

Basic DL/I Terminology

Basic DL/I Data Base Processing

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Hierarchical StructuresHierarchical Structures

In a DL/I data base, data elements are organized in ahierarchical 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.

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W hy a data base manag ement system? W hy a data base manag ement 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 Terminolog yBasic DL/I Terminolog y

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

HouseNumber

Street

Name

City State Country ZipCode

Fig 1.3 The ADDRESS segment with six fields

Segment Type

A category of data

There can be a maximum of 255 segment types and 15

levels in one data base

Segment Occurrence

One specific segment of a particular type containing user

data

Note:-

Within a data base there is only one of each segment type- it¶s part of

the data base¶s definition- but there can be an unlimited number of

occurrences of each segment type.

The word µsegment¶ is used to mean either µsegment type¶ or µsegment

occurrence¶ and usually the meaning is clear from the context

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Basic DL/I Terminolog y (contd.)Basic DL/I Terminolog y (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).

05 IVS-VENDOR-CONTACT PIC X(30).

*

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.

05 ISLS-LAST-REORDER-DAT PIC X(6).

*

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

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Basic DL/I Terminolog y (contd.)Basic DL/I Terminolog y (contd.)

R oot Segment The segment type at the top of a hierarchy

Data base record

Each occurrence of the root segment plus all the

segment occurrences that are subordinate to it make up

one data base record

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

subordinate segment occurrences

Data baseR ecord 1

Data baseR ecord 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

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

Sequential Processing When you retrieve segments from a data basesequentially, DL/I follows a predictable pattern: down thehierarchy, then right.

Position

At any point, a program has a position in the data base.

Position can affect not only how segments are retrieved, but

how new segments are inserted as well

Data baseR ecord 1

Data base

R ecord 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

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

R andom (Direct) Processing Many applications require that a data base be processed

randomly rather than sequentially

Segments that you need to access randomly normally

contain a key field (or sequence field)

Concatenated Key

Completely identifies the path from the root segment to thesegment you want to retrieve.

Concatenated Key:

Vendor 2 Item 1

Location 1

Fig 1.9 R andom Processing

Data baseR ecord 1

Data baseR ecord 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

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Module 2Module 2An Introduction to DL/I Prog rams and An Introduction to DL/I Prog rams and

Control BlocksControl Blocks

The IMS Software Environment

How DL/I relates to your application programs

Control Blocks

DBDGEN

PSBGEN

How to run an application program that uses DL/I

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The IMS Software EnvironmentThe IMS Software Environment

Application

Programs

IMS Control

Blocks

DL/I

OS

Data

Base

IMS DC Remote

Terminal

Fig 2.1 The IMS Software Environment

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How DL/I relatesHow DL/I relatesto your application prog rams (contd.)to your application prog rams (contd.)

Standard file processing Application programs issue standard COBOL statementslike R EAD and W R ITE

These statements invoke the appropriate access method,like VSAM to transfer data between records if necessary

The format of the record that is processed by your program is the same as the format of the record on disk

DL/I data base processing DL/I acts as an interface between an application programand the access method

To perform an operation on a DL/I data base, a programdoesn¶t issue a standard COBOL file I/O statement

Instead it executes a CALL statement to invoke DL/I

The parameters passed by the call tell DL/I what operation to perform

Then, DL/I, not the application program, invokes theaccess method

DL/I uses a standard access method- usually VSAM- tostore data base data on disk

In fact, the access method doesn¶t know that a particular data set contains a data base instead of a standard file

Format of records in a data base data set probably doesn¶t match the layouts of the segments that make upthe data base

As a result, the way the program sees the data basediffers from the way the access method sees it.

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Control BlocksControl Blocks

The physical structure of a DL/I data base isn¶t specified in application programs

Instead, DL/I uses a set of control blocks to define adata base¶s structure

In particular, DL/I uses two types of control blocks:DBDs and PSBs

Data Base Description (DBD)Describes the complete structure of a data base

An installation must create one DBD for each DL/I database

Program Specification Block (PSB)

Although each data base has a single physical structurethat is defined by a DBD, the application programs that

process it can have different views of it These views, also called application data structures,specify

The data bases (one or more) a program can access,

The data elements the program can ³see´ in those databases, and,

The processing the program can do.

This information is specified in a PSB Although each application program can have its ownPSB, it is not uncommon for application programs that have similar data base processing requirements to sharea PSB

Creating DL/I control blocks is the responsibility of aData Base Administrator (DBA)

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DBDGENDBDGENSTMT SOURCE STATEMENT

1 PRINT NOGEN

2 DBD NAME=INDBD,ACCESS=HIDAM

3 DATASET DD1=IN,DEVICE=3380

4 **/ 3380 DISK STORAGE

5 *

6 SEGM NAME=INVENSEG, PARENT=0,POINTER=TB,BYTES=131

7 LCHILD NAME=(INPXPNTR,INPXDBD),POINTER=INDX

8 FIELD NAME=(INVENCOD,SEQ),BYTES=3,START=1,TYPE=C

9 FIELD NAME=INVENNAM,BYTES=30,START=4,TYPE=C

10 FIELD NAME=INVENADR,BYTES=30,START=34,TYPE=C

11 FIELD NAME=INVENCIT,BYTES=17,START=64,TYPE=C

12 FIELD NAME=INVENSTA,BYTES=2,START=81,TYPE=C

13 FIELD NAME=INVENZIP,BYTES=9,START=83,TYPE=C

14 FIELD NAME=INVENTEL,BYTES=10,START=92,TYPE=C

15 FIELD NAME=INVENCON,BYTES=30,START=102,TYPE=C

16 *

17 SEGM NAME=INITMSEG,PARENT=INVENSEG,BYTES=48

18 FIELD NAME=(INITMNUM,SEQ),BYTES=5,START=1,TYPE=C

19 FIELD NAME=INITMDES,BYTES=35,START=6,TYPE=C

20 FIELD NAME=INITMPRC,BYTES=4,START=41,TYPE=P

21 FIELD NAME=INITMCST,BYTES=4,START=45,TYPE=P

22 *

23 SEGM NAME=INLOCSEG, PARENT=INITMSEG,BYTES=21

24 FIELD NAME=(INLOCLOC,SEQ),BYTES=3,START=1,TYPE=C

25 FIELD NAME=INLOCONH,BYTES=4,START=4,TYPE=P

26 FIELD NAME=INLOCROP,BYTES=4,START=8,TYPE=P

27 FIELD NAME=INLOCONO,BYTES=4,START=12,TYPE=P

28 FIELD NAME=INLOCDAT,BYTES=6,START=16,TYPE=C

29 *

30 DBDGEN

72 **/**************************************************************************

73 **/ RECOMMENDED VSAM DEFINE CLUSTER PARAMETERS

74 **/**************************************************************************

75 **/* * NOTE2

76 **/* DEFINE CLUSTER (NAME(IN) NONINDEXED -

77 **/* RECORDSIZE (2041,2041) -

78 **/* COUNTERINTERVALSIZE (2048))

79 **/* * NOTE2 - SHOULD SPECIFY DSNNAME FOR DD IN

80 **/**************************************************************************

162 **/***********SEQUENCE FIELD*************

211 **/***********SEQUENCE FIELD*************

236 **/***********SEQUENCE FIELD*************

325 FINISH

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

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DBDGEN (contd.)DBDGEN (contd.)

Explanation of Fig 2.3The first macro± DBD± identifies the data base

The DBD macro names the data base (NAME=INDBD) and specifies the DL/I access method that will be used for it (ACCESS=HIDAM)

The second macro, DATASET, identifies the file that will contain the data base

In this case, its symbolic name will be IN (DD1=IN), and it will reside on a 3380 disk unit (DEVICE=3380)

The symbolic name is used in the JCL to identify the dataset at execution time

Lines 72 through 80 are produced at assembly time and give recommendations for the VSAM file that will containthe inventory data base

The segment types are defined using the SEGM macroThe hierarchical relationships among the segments arespecified by coding the PAR ENT parameter on eachSEGM macro

PAR ENT= 0 or absence of PAR ENT parameter specifies root segment

The POINTE R parameter in the first SEGM macro and the

LCHILD macro that follows are required because the DBAspecified HIDAM in the DBD macro

DBA does not have to define each field in the segment,because application programs identify fields within it in asegment layout.

Only search fields need to be specified

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DBDGEN (contd.)DBDGEN (contd.)

To define a field in the DBD, the DBA codes a FIELDmacro, which can contain the following parameters

NAME name of the field (1 to 8 characters long)

START position of field within segment

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

The SEQ parameter is used to specify a sequence field

When occurrences of these segments are added to the data

base, they are added in sequence by values in these fields

Fig 2.4 FIELD macro TYPE parameter codes

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PSBGENPSBGEN

STMT SOURCE STATEMENT

1 PRINT NOGEN

2 PCB TYPE=DB,DBDNAME=INDBD,PROCOPT=LS

3 SENSEG NAME=INVENSEG

4 SENSEG NAME=INITMSEG,PARENT=INVENSEG

5 SENSEG NAME=INLOCSEG,PARENT=INITMSEG

6 PSBGEN PSBNAME=INLOAD,LANG=COBOL

87 END

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

Explanation of Fig 2.5

The first macro in the PSBGEN job stream is PCB

PCB (Program Communication Block) describes one database.

A PSBGEN job contains one PCB macro for each data

base the application program can access.The PSB in the figure is one for a program that accessesa single data base with segment level sensitivity

Segment Level Sensitivity

The program¶s access to parts of the data base is identified at the segment level

Within the segments to which it is sensitive, the program has

access to all fields A program can also have field level sensitivity

Within sensitive segments, only specific fields are identified as sensitive fields

When the program accesses that segment, only sensitivefields are presented

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PSBGEN (contd.)PSBGEN (contd.)

The DBDNAME parameter on the PCB macro specifiesthe name of the DBD for the data base to which the PCB

corresponds

The KEYLEN parameter specifies the length of the

longest concatenated key the program can process in the

data base

The P R OCOPT parameter specifies the program¶s

processing optionsIndicate what processing the program is allowed to perform

on the data base

LS The program can perform only load operations

Other values can authorize programs to retrieve, insert,

replace, and delete segments

This parameter can be used by the DBA to control access to

the database more selectively than is possible at the database level

For each PCB macro, subordinate SENSEG macros

identify the segments in the data base to which the

application program is sensitive

The 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

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How to run anHow to run an

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How to run an How to run an application prog ram that uses DL/Iapplication prog ram that uses DL/I

A batch program that processes a DL/I data base is not run directly

Instead, the programmer supplies JCL to invoke the

DL/I µbatch initialization module¶, which in turn loads

the application program and the DL/I modules required

to service it.

Under IMS, the batch initialization module isDFS RR C00

The program and DL/I modules execute together

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The ENTRY andThe ENTRY and

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The ENTRY andThe ENTRY andGO BACK StatementsGO BACK Statements

ENTRY µDLITCBL¶ USING PCB-name1

[PCB-name2...]

Fig 3.1 Format of the DL/I ENT R Y Statement

The application program is invoked under the control of the

batch initialization module

DL/I first loads the appropriate control blocks and modules,

then loads the application program and passes control to it

DLITCBL, which stands for µDL/I to COBOL¶ is declared as the

entry point to the program by coding the ENT R Y statement

When DL/I passes control to the program, it also supplies the

address of each PCB defined in the program¶s PSB, in much

the same way as parameters are passed to a called subprogram

Since these PCBs reside outside the program they must be

defined in the Linkage Section, just like passed parameters

would be defined in a subprogram

The Linkage Section definition of a PCB is called a µPCB

Mask¶

Addressability to PCBs- that is, the way the programmer

relates PCB masks in your program¶s Linkage Section to

actual PCBs in storage- is established by listing the PCB

Masks on the ENT R Y statement

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The DL/I CallThe DL/I Call

CALL statements are used to request DL/I servicesThe parameters you code on the CALL statement

specify, among other things, the operation you want

DL/I to perform

CALL µCBLTDLI¶ USING DLI-function

PCB-mask

segment-io-area

[segment-search-argument(s)]

Fig 3.2 Format of the DL/I call

CBLTDLI, which stands for µCOBOL to DL/I¶, is thename of an interface module that is link edited with

your program¶s object module.

If you work on PL/I, you would specify PLITDLI and for

assembler language, you would specify ASMTDLI

Th DL/I C ll ( d )Th DL/I C ll ( d )

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

The DL/I FunctionThe first parameter coded on any DL/I call

For this parameter, you supply the name of a four character working storage field that contains the code for the function you want

01 DLI-FUNCTIONS.

05 DLI-GU PIC X(4) VALUE µGU ¶.05 DLI-GHU PIC X(4) VALUE µGHU ¶.

05 DLI-GN PIC X(4) VALUE µGN ¶.

05 DLI-GHN PIC X(4) VALUE µGHN ¶.

05 DLI-GNP PIC X(4) VALUE µGNP ¶.

05 DLI-GHNP PIC X(4) VALUE µGHNP¶.

05 DLI-ISRT PIC X(4) VALUE µISRT¶.

05 DLI-DLET PIC X(4) VALUE µDLET¶.

05 DLI-REPL PIC X(4) VALUE µREPL¶.

05 DLI-CHKP PIC X(4) VALUE µCHKP¶.

05 DLI-XRST PIC X(4) VALUE µXRST¶.

05 DLI-PCB PIC X(4) VALUE µPCB ¶.

Fig 3.3 DL/I function codes

For specifying the DL/I function, the programmer would code one of the 05 level data names (like DLI-GN) in aDL/I call, since COBOL doesn¶t let you code literals on aCALL statement

Th DL/I C ll ( td )Th DL/I C ll ( td )

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Get functionsThe first six 05-level items in Fig 3.3 are get functions

They are used to retrieve segments from a DL/I data base

GU µget unique¶ function causes DL/I to retrieve a specific

segment occurrence based on field values that you specify.

GN µget next¶ function used to retrieve segment

occurrences in sequence

GNP

µget next within parent¶ function lets you retrievesegment occurrences in sequence, but only subordinate to

an established parent segment

The three get function codes that contain an H are µget hold

functions¶ and are used to specify an intent to update a

segment after you retrieve it

GHU or the µget hold unique¶ function corresponds to GU

GHN or the µget hold next¶ function corresponds to GN

GHNP or the µget hold next within parent¶ function

corresponds to GNP

Update functions

Used to change data in the data base

IS R T or the µinsert¶ 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 µdelete¶ function is used to remove a segment

from a data base

R EPL or the µreplace¶ function is used to replace a segment

occurrence

Th DL/I C ll ( td )Th DL/I C ll ( td )

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Other functionsFunctions CHKP (the µcheckpoint¶ function) and X R ST (the

µrestart¶ function) are used in programs to take advantage of

IMS¶s recovery and restart features

The last function code PCB is used in CICS programs

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

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The PCB mask The second parameter on the DL/I call

The name of the PCB mask defined in the program¶s

Linkage Section

The ENT R Y statement establishes a correspondence

between PCB masks in the Linkage Section and the PCBs

within the program¶s PSB

So, when you code a particular PCB mask on a DL/I call,

you tell DL/I which data base to use for the operation you

are requesting

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 AreaThe third parameter on the DL/I call

The 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

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

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Segment search argumentsOptional parameter on the DL/I call

An SSA identifies the segment occurrence you want to

access

Depending on the call you are issuing and the structure

of the data base, you may have to code several SSAs on

a single DL/I call

The structure of the SSAs can vary from simple to

complex

You can code as many SSAs as required

There are two kinds of SSAs± unqualified and qualified

An unqualified SSA

Supplies the name of the next segment type that you want to

operate on

For instance, 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 segment occurrence to be processed

For example, a GU call with a qualified SSA might request a

particular occurrence of a named segment type by providing

a key value

The PCB MaskThe PCB Mask

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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)

You define masks for those areas of storage in the

Linkage Section of your program

Then, after establishing the proper linkage to them at

the start of your program, you can evaluate data DL/I stores there for information about the data bases your

program can process

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 the Inventory data base

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

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

Data base nameThe 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 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

On the other hand, 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

Indicates the processing a program is allowed to do on

the data baseSegment name feedback area

The name of the segment is stored by DL/I in this field

after each DL/I call.

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Types of SSAsTypes of SSAs

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ypyp

An SSA identifies the segment occurrence you want toaccess

It can be either

Qualified, or,

Unqualified

An unqualified SSA simply names the type of segment

you want to use A qualified SSA, on the other hand, 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

Basic Unqualified SSABasic Unqualified SSA

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qq

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 blanksThe 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

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

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q ( )q ( )

Unqualified SSA shown in Fig 4.1 was generalized

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 µINVENSEG¶ TO UNQUAL-SSA-SEGMENT-NAME

MOVE µINITMSEG¶ 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 µINVENSEG ¶.

*

01 UNQUAL-ITEM-SSA PIC X(9) VALUE µINITMSEG ¶.

*

01 UNQUAL-STOCK-LOC-SSA PIC X(9) VALUE µINVENSEG ¶.

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Command CodesCommand Codes

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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

Command Codes (contd.)Command Codes (contd.)

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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 variablecommand code is shown below

01 UNQUALIFIED-SSA.

*


05 FILLER PIC X VALUE ³*´

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


*

Command Codes (contd.)Command Codes (contd.)

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Command Code Meaning

C Concatenated Key

D Path Call

F First Occurrence

L Last OccurrenceN 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 codes

Fig 4.5 SSA Command Codes

The Null Command CodeThe Null Command Code

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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 ³*´.

05 UNQUAL-SSA-COMMAND-CODE PIC X VALUE ³-´.


*

Multiple QualificationsMultiple Qualifications

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There are two cases in which you would use multiple

qualificationWhen 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 a rangeof 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 ANDand O R

Either of the two symbols shown in the table below may be used for AND or O R

The independent AND operator is used for special operations with secondary indexes and will bediscussed later

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

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01 VENDOR-SSA.

*

05 FILLER PIC X(9) VALUE µINVENSEG(¶.

05 FILLER PIC X(10) VALUE µINVENCOD>=¶.

05 VENDOR-SSA-LOW-CODE PIC X(3).

05 FILLER PIC X VALUE µ&¶.

05 FILLER PIC X(10) VALUE µINVENCOD<=¶.

05 VENDOR-SSA-HIGH-CODE PIC X(3).

05 FILLER PIC X VALUE µ)¶.

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 therange to VENDOR-SSA-LOW-CODE and VENDOR-SSA-HIGH-CODE

Then you would execute GN calls that include VENDOR-SSA

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The GU CallThe GU Call

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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 µCBLTDLI¶ USING DLI-GU

INVENTORY-PCB-MASK

INVENTORY-STOCK-LOC-SEGMENT

VENDOR-SSA

ITEM-SSA

STOCK-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 µfully

qualified call¶

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

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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 asegment that met the criteria you specified in the call

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The GNP CallThe GNP Call

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CALL µCBLTDLI¶ USING DLI-GNP

INVENTORY-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 theestablished parentage DL/I returns GE as the status

code

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Status Codes you can expect during Status Codes you can expect during Sequential Processing Sequential Processing

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Using Command Codes with Retrieval CallsUsing Command Codes with Retrieval Calls

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The F command code

When you issue a call with an SSA that includes the F command code, the call processes the first occurrence of the segment named by the SSA, subject to the call¶sother qualifications

Can be used when you are doing sequential processing and you need to back up in the data base, or in other words, the F command code can be used for sequential

retrieval using GN and GNP callsMeaningless with GU calls, because GU normally retrieves the first segment occurrence that meets thecriteria you specify

The L command code

When you issue a call with an SSA that includes the Lcommand code, the call processes the last occurrence of

the segment named by the SSA, subject to the call¶sother qualifications

The D command code

Used to retrieve more than one segment occurrenceusing just one call

Normally 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 levelsas well

Makes it easy to retrieve an entire path of segments

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Using Command Codes with Retrieval CallsUsing Command Codes with Retrieval Calls(contd.)(contd.)

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The C command code

If you are developing a program that retrieves just lower- level segment occurrences from a data base, you don¶t have to code separate SSAs for each level in thehierarchical path

Instead you can use a single SSA with the C command code

Then, rather than coding a field name, relational operator,

and search value, you specify the concatenated key for the segment you are interested in

An illustration of the use of the C command code isshown below

*

01 LOCATION-SSA.

*

05 FILLER PIC X(11) VALUE µINLOCSEG*C(µ.

05 LOCATION-SSA-VENDOR PIC X(3).

05 LOCATION-SSA-ITEM PIC X(5).

05 LOCATION-SSA-LOCATION PIC X(3).


*

.

.

.CALL µCBLTDLI¶ USING DLI-GU

INVENTORY-PCB-MASK


LOCATION-SSA.

Using Command Codes with Retrieval CallsUsing Command Codes with Retrieval Calls(contd.)(contd.)

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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 SSAThe 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 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 code

Effect 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

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Multiple Processing Multiple Processing

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Multiple processing is a general term that means a

program can have more than one position in a single physical data base at the same time

DL/I lets the programmer implement multiple

processing in two ways

1. Through multiple PCBs

2. Through multiple positioning

Multiple PCBs

The DBA can define multiple PCBs for a single data base

Then, the program has two (or more) views of the data

base

As with PCBs for different data bases, each has its own

mask in the Linkage Section and is specified in the

ENT R Y 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

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

M lti l iti i

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Multiple positioning

Lets a program maintain more than one position within adata 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

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Module 6Module 6Adding and Updating DataAdding and Updating Data

in a Data Basein a Data Base

The IS R T Call

The Get Hold Calls

The R EPL Call

The DLET Call

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

A f t h i i t if lifi d SSA f h

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A safer technique is to specify a qualified SSA for each

hierarchical level above the one where you want toinsert the segment, as illustrated below

CALL µCBLTDLI¶ USING DLI-ISRT

INVENTORY-PCB-MASK


VENDOR-SSA ITEM-SSA

UNQUALIFIED-SSA.

If SSAs for vendor and item are initialized with the

proper key values, DL/I inserts the new segment

occurrence in the correct position in the data base

When you issue a fully qualified IS R T 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 IS R T call with qualified

SSAs instead of first issuing GU calls to find out if

higher-level segments in the path are present By issuing one call instead of two (or more), you can

save system resources

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

Wh i t d t t d

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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 don¶t have

sequence fields at all

When that¶s the case, where the segment occurrence isadded 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 ³first´, the new segment is added before any

existing twinsIf the rule is ³last´, the new segment is added after all

existing twins

If the rule is ³here´, 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

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The Get Hold CallsThe Get Hold Calls

There are three get hold functions you can specify in a

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There are three get hold functions you can specify in a

DL/I call:1. GHU (Get hold unique)

2. GHN (Get hold next), and,

3. GHNP (Get hold next within parent)

These calls parallel the three retrieval calls earlier

discussed

Before you can replace or delete a segment, you must

declare your intent to do so, by retrieving the segment

with one of these three calls

Then you must issue the replace or delete call before

you do another DL/I processing in your program

The REPL CallThe REPL Call

After you have retrieved a segment with one of the get

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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 R EPL 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 R EPL call: if you do,

the call will fail

An example of a typical replace operation is shown

below CALL µCBLTDLI¶ 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 µCBLTDLI¶ USING DLI-REPL

INVENTORY-PCB-MASK

INVENTORY-STOCK-LOC-SEGMENT.

The REPL Call (contd.)The REPL Call (contd.)

Status codes you can expect during replace

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Status codes you can expect during replace

processing If you try to use a qualified SSA on an R EPL 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 R EPL call, DL/I returns a DA

status code

The DLET CallThe DLET Call

The DLET call works much like R EPL

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You must first issue a get hold call to indicate that you intend to make a change to the segment you areretrieving

Then you issue a DLET call to delete the segment occurrence from the data base

For example, to delete a stock location that is no

longer active, you¶d code a series of statements likethe ones below CALL µCBLTDLI¶ USING DLI-GHU

INVENTORY-PCB-MASK


VENDOR-SSA

ITEM-SSA

LOCATION-SSA.CALL µCBLTDLI¶ 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 DLET call± when you delete a

segment, you automatically delete all segment occurrences subordinate to it

The status codes you might get after a DLET call arethe same as those you can get after an R EPL call

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Module 7Module 7Secondary Indexing Secondary Indexing

The Need for Secondary Indexing

A Customer Data Base

Secondary Indexes

Secondary Keys

Secondary Data Structures

DBDGEN R equirements for Secondary Indexes

PSBGEN R equirements for Secondary Indexing

Indexing a Segment based on a Dependent Segment

The Independent AND Operator

Sparse Sequencing

Duplicate Data Fields

The Need for Secondary Indexing The Need for Secondary Indexing

Often you need to be able to access a data base in an

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y

order other than its primary hierarchical sequenceOr, you may need to access a segment in a data base

directly, without supplying its complete concatenated

key

With secondary indexing both are possible

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

01 CUSTOMER-SEGMENT.

05 CS-CUSTOMER-NUMBER PIC X(6).

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( )

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.

05 RS-CASH-DISCOUNT PIC S9(5)V99 COMP-3.

05 RS-SALES-TAX PIC S9(5)V99 COMP-3.

05 RS-FREIGHT PIC S9(5)V99 COMP-3.

05 RS-BALANCE-DUE PIC S9(5)V99 COMP-3.

*

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

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

01 PAYMENT-SEGMENT.

05 PS-CHECK-NUMBER PIC X(16).

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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)

Secondary IndexesSecondary Indexes

Invoice number index data base

Secondary Index

Data BaseCustomer Data Base

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Customer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Prefix DataRec. Seg.

Addr.

Invoice

No.Index

Pointer

Segment

Indexed Data

Base

Index Target

SegmentIndex Source

Segment

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

Secondary Indexes (contd.)Secondary Indexes (contd.)

DL/I maintains the alternate sequence by storing

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pointers to segments of the indexed data base in aseparate 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

Secondary Indexes (contd.)Secondary Indexes (contd.)

If multiple access paths are required into the same

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data base, the DBA can define as many different secondary indexes as necessary± each stored in a

separate index data base

In practice, the number of secondary indexes for a given

data base is kept low because each imposes additional

processing overhead on DL/I

Secondary KeysSecondary Keys

The field in the index source segment over which the

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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 asfive 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 StructuresSecondary Data Structures

A secondary index changes the apparent hierarchical

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structure of the data baseThe 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 besubordinate 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

Secondary Data Structures (contd.)Secondary Data Structures (contd.)

Secondary data structures don¶t change the way the

d t b t t d di k

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data base segments are stored on disk They just alter the way DL/I presents those segments to

application programs

When you code an application program that processes

a data base via a secondary index, you must consider

how the secondary data structure affects your

program¶s logic

DBDGEN Requirements forDBDGEN Requirements forSecondary IndexesSecondary Indexes

Because a secondary index relationship involves two

d t b t DBDGEN i d f th

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data bases, two DBDGENs are required± one for theindexed 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 toimplement the secondary index

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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

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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±

C RR ECXNO

The XDFLD macro in Fig 7.5 supplies a field name

(C RR ECXNO) 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 S R CH parameter defines the field(s) that

constitute the secondary index

PSBGEN Requirements forPSBGEN Requirements forSecondary Indexing Secondary Indexing

Just because a secondary index exists for a data base

doesn¶t mean DL/I will automatically use it when one of

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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 P R OCSEQ parameter of the PSB macro

If it doesn¶t, processing is done using the normal

hierarchical sequence for the data baseFor the P R OCSEQ parameter, the DBA codes the DBD

name for the secondary index data base that will be

used

Fig 7.7 PSBGEN Output

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

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data structure imposed by the secondary index When the P R OCSEQ 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 theP R OCSEQ parameter

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

C tInvoice number index data base

Secondary Index Data Base

Customer Data Base

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Customer

Ship-to

Buyer Receivable

Payment Adjustment Line Item

Prefix Data

Cust. Seg.Addr.

ItemNo.

IndexPointer

Segment

Indexed Data Base

Index TargetSegment

Index SourceSegment

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

Indexing a SegmentIndexing a Segmentbased on a Dependent Segment (contd.)based on a Dependent Segment (contd.)

The Index Source Segment and the Index Target

Segment need not be the same

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Segment need not be the sameSome 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 customersbased 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 in the customer segment, because the customer segment is superior to the line item segment

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

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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 µCRCUSSEG(¶.

05 FILLER PIC X(10) VALUE µCRLINXNO =¶.

05 SSA-ITEM-KEY-1 PIC X(8).

05 FILLER PIC X VALUE µ#¶.

05 FILLER PIC X(10) VALUE µCRLINXNO =¶.

05 SSA-ITEM-KEY-2 PIC X(8).


Sparse Sequencing Sparse Sequencing

When the DBA implements a secondary index database with sparse sequencing (also called sparseindexing), it is possible to omit some index source

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g), psegments from the index

Sparse sequencing can improve performance whensome occurrences of the index source segment must be indexed but others need not be

DL/I uses a suppression value, a suppression routine,

or both to determine whether a segment should beindexed (either when inserting a new segment or processing an existing one)

If the value of the sequence field(s) in the index sourcesegment matches a suppression value specified by theDBA, 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 thesegment

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

Note:

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

You don¶t need to make special provisions for it in your application program

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Module 8Module 8Log ical Data BasesLog ical Data Bases

Introduction to Logical Data Bases

Logical Data Base Terminology

DBDGENs for Logical Data Bases

An Introduction to Log ical Data BasesAn Introduction to Log ical Data Bases

Inter related databases.

A logical child segment having 2 parent segments.One physical parent and one logical parent

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One physical parent and one logical parent.

SEG-a SEG-b RLC

PP

C2

SEG-1

LP

VLC

Virtual Logical Child

R eal Logical Child

DB1

DB2

Logical Parent

Physical Parent

Log ical Data Base Terminolog yLog ical Data Base Terminolog y

R eal Logical Child

The child under consideration

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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.The child accesses logical parent¶s data but the reverse isnot allowed.

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

Bi-directional physical.

Accesses in both the directions, but the child exists both inthe physical DB as well as the logical DB.

DBDGENs for a Log ical Data BaseDBDGENs for a Log ical Data Base

******DBD1******

.

.

.

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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 9Module 9Recovery and RestartRecovery and Restart

Introduction to Data Base R ecovery

Introduction to Checkpointing

Types of Checkpointing

Extended R estart

Introduction to Data Base RecoveryIntroduction to Data Base Recovery

The process of recovering the data base in case of

application program failureBack out changes made by the abended program,

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g y p g

correct the error and rerun the program.

Types of recoveries

Forward recovery

Backward recovery

Forward R ecovery 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 forward

recovery

Used when a data base is physically damaged

Backward R ecovery

Data 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 backout 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

Introduction to Checkpointing Introduction to Checkpointing

Synonyms: synchronization point, sync point, commit

point and point of integrity Program execution point at which the DB changes are

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complete and accurate

DB changes made before the most recent checkpoint

are not reversed by recovery

Normally the start of the pgm is considered as a

default checkpoint In case of a number of DB updates, explicit

checkpoints can be specified

Explicit checkpoints can be established using

checkpoint call(CHKP) inside the program

CHKP creates a checkpoint record on DL/I log which

prevents recovery before that point

Types of Checkpointing Types of Checkpointing

Types of checkpointing

Basic checkpointing Symbolic checkpointing

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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

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 X R ST

(Extended R estart) call too.

Extended Restart (XRST)Extended Restart (XRST)

The X R ST call is used in connection with the symbolic

checkpoint call It is used to restart your program

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The X R ST call precedes a symbolic checkpoint call

The X R ST 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 X R ST call

Specifying ID in the CKPTID= field of EXEC statement in

the program's JCL

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Module 10Module 10Advanced DL/I featuresAdvanced DL/I features

Variable Length Segments

DBD for GSAMs

PCB for GSAMs

Variable Leng th SegmentsVariable Leng th 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

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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 longest possible

text then 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 IS R T / R EPLACE / DELETE call is issued we

have to move the actual length to the length field in the

I/O area

Variable Leng th Segments (contd.)Variable Leng th Segments (contd.)

Variable Length Segments are appropriate when

segment occurrence length vary but once created and

made stabilized.

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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

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

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the application retrieves data from the database

The DD name of the output dataset used when loading

the database.

The DBD for a GSAM is shown below DBD NAME=CARDS,ACCESS=(GSAM,BSAM)

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

DBDGEN

FINISH

END

In GSAM DBD's you can't specify SEGM and FIELD statements

The use of logical or index relationships between

segments

IMS adds 2 bytes to the record length value specified

in the DBD in order to accommodate the ZZ field that is

needed to make up the BSAM R DW.

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

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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 R ESTAR T

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 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

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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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Module 11Module 11DL/I Data Base OrganizationsDL/I Data Base Organizations

DL/I Organizations & Access Methods

Hierarchical Sequential Organization

Hierarchical Direct Organization

Additional IMS Access Methods

DL/I Organization & Access MethodsDL/I Organization & Access Methods

File Organization is a description of how a file is

processed & access method is the software used to

implement that processing.

DL/I provides two basic data base organizations :

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p g

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.

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Hierarchic Direct OrganizationHierarchic Direct OrganizationAccess 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

d th b t f i t th HD

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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.

R oot segments can be retrieved in sequence.

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

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through DL/I calls.

Processing of database is sequential , IS R T add data only

at the end of database & R EPL and DLET calls are not

supported.

They are typically used during conversion from a systemthat 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 provides 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 asmall amount of data.

These are root-segment-only data bases.

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

DEDB( Data Entry Data Base ) :

DEBD is stored in a disk and has a hierarchical structure

They are organized in typical DL/I fashion, as direct

dependent segments types.

DEBD li t d t h th t i l

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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

ACB & ACBGENACB & 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 b ilding ACB is called Block

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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 ACB maintenance 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.

Sample JCLSample JCL

//JOBNAME JOB (ACCT),'PGMR NAME',

// CLASS=J,

//MSGCLASS=Z,

// NOTIFY=&SYSUID

//JOBLIB DD DSN=YOUR.PROGRAM.LOAD.LIBRARY,

// DISP=SHR

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// DD DSN=YOUR.SYSTEM.RESLIB.LIBRARY,

// DISP=SHR

//PROC EXEC PROCNAME, SYMBOLIC PARAMETERS

//****************************************************************

//PROCNAME PROC//****************************************************************

//* THIS STEP LOADS INTO AN IMS VSAM DATABASE

//* A COBOL PROGRAM 'LOAD' IS USED FOR THIS

//*PURPOSE

//* THE PSB USED FOR LOADING IS LOADPSB

//****************************************************************

//LOAD EXEC PGM=DFSRRC00,

// PARM='DLI,LOAD,LOADPSB'

//*

//DFSRESLB DD DSN=YOUR.DFRESLIB.LIBRARY,

// DISP=SHR

//IMS DD DSN=YOUR.DBD.LIBRARY,

// DISP=SHR

// DD DSN=YOUR.PSB.LIBRARY,

//DISP=SHR

//*

Sample JCL (contd.)Sample JCL (contd.)

//IMSLOGR DD DSN=YOUR.IMSRLOG.DATASET,

// DISP=SHR

//*

//IEFRDER DD DSN=YOUR.IEFRDER.DATASET,

// DISP=(,DELETE,DELETE),UNIT=&UNITDA,

// CB=(RECFM=&RECFM,LRECL=&LRECL,

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// BLKSIZE=&BLKSIZE), SPACE=&SPACE

//*

//* DD NAMES ARE AS SPECIFIED IN THE DATABASE

//* DBD

//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 12Module 12Miscellaneous TopicsMiscellaneous Topics

Data base image copy

Path Call

IMS Processing Options

IMS Status Codes

IMS Abends

Key, search and concatenated key fields

Data Base Imag e CopyData Base Imag e 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

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y

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

Path CallPath Call

A DB call with an SSA that includes the 'D' Command code is a "PATH CALL³ . It¶s a facility where in we can

retrieve an entire path of the segment Consider a sample GU call

CALL 'CBLTDLI' USING DLI-GU

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INVEN-PCB-MASK

INVEN-STOCK-LOC-SEG

VENDO R -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 theabove E.g.)

In case if we need data from not just from the lowest level but from other levels as well we normally have to

give 3 separate GU calls.This will reduce the efficiency of the program

Such a call operates on two or more segments rather than just one segment.

If a program has to use "Path call" then "P" should beone of the values specified in the P R OCOPT

parameter of the PCB in the programs PSBGEN.If path call is not explicitly enabled in the PSBGEN jobthere will be an 'AM' status code.

Sample Prog ramSample Prog ram

IDENTIFICATION DIVISION.

PROGRAM-ID. PATGET2.

ENVIRONMENT DIVISION.

CONFIGURATION SECTION.

SOURCE-COMPUTER. IBM-370.

OBJECT-COMPUTER. IBM-370.

INPUT-OUTPUT SECTION.

FILE-CONTROL.

DATA DIVISION.

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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).

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).

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Sample Prog ram (contd.)Sample Prog ram (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

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MOVE INTENSIVE TO WARD-TYPE.

CALL 'CBLTDLI' USING WS-ISRT

PCB-MASK

WARD-I-O-AREA

UNQUAL-HOSPITAL-SSA

UNQUAL-WARD-SSA.


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.


EXIT.

INSERT-PATIENTS-EXIT.EXIT.

IMS Processing OptionsIMS Processing Options

Indicates to IMS the type of access allowed for a

sensitive segment (SENSEG)

Commonly used Processing Options

P R OCOPT=G means only read only access

P R OCOPT=R means read/replace access

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P R OCOPT=I means insert access allowed

P R OCOPT=D means R ead/Delete access

P R

OCOPT=A means all the above options present For GSAM DBs P R OCOPT=LS for output and GS (Get

Sequential) for input

P R OCOPT=L allows a 'load' into the DB. If VSAM DB, it

should be empty prior to the load

The P R OCOPT given for a Sensitive segment would

override the one given for the DB

Example : -

PCB

TYPE=DB,NAME=LDB42F,P R OCOPT=G,KEYLEN=200

SENSEG NAME=SEGL4201,PAR ENT=0,P R OCOPT=A

WAR NING : Indiscriminate use of P R OCOPTS might lead

to inexplicable results !

IMS Status CodesIMS Status Codes

R eturned by IMS after each DB call Field STATUS-CODE X(02) in the PCB-MASK definition

Acceptable and unacceptable status codesµGE¶ ± record occurrence not found

µGB¶ ± End of DB reached

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Status codes relate to the type of IMS call

DLET ± AB, AJ, DJ AB ± I/O area not specified in the call

AJ ± Invalid SSA format (invalid command code etc)

DJ ± Segment not in µHOLD¶ status

GHN, GHNP, GHU, GU ± AB, AK, GE, GB

AK ± Invalid field name in SSA

IS R T ± AB, AC, AD, AJ, AK, II

AC ± Segment not found

AD ± Wrong PCB used

II -- Segment occurrence already exists in the DB

R EPL -- AB, AC, AD, DJ

IMS AbendsIMS Abends

U0456 -- PSB stopped

U0456 -- IMS Compile option µDLITCBL¶ not set to µY¶

U0458 -- DB Stopped

U0844 -- DB being updated is full

S013 -- Error opening the DB

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S013 Error opening the DB

A few tips on resolving IMS abends:

Confirm that the Abend is caused by IMS ± check the

joblog for IMS return code

Check the JCL ± if modified from another JCL, verify

that changes are correct

Check the SYSOUT dump for IMS diagnostic

messagesUse MVS/QW to get further information on the abend

Key, Search and Concatenated Key FieldsKey, Search and Concatenated Key Fields

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

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If in a root segment, key field uniquely identifies the

record

Additional Search fields

Used to search through the DB for particular values

Max 255 search fields in a segment

Concatenated field

Key formed to access a particular segment Concatenation of keys of root segment and all

successive children down to the accessed segment

Undefined fields

Fields not defined to IMS

Format determined by the program loading the DB

8/6/2019 IMS DB-Apr2002


Apr 3, 2002 IMS DB Page : 132/132

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ims db-apr2002

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