IMS-DB

Information Management SystemDB Concepts & Programming

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Files Vs DatabasesNetworked,Hierarchical & Relational structureAccess types - HSAM, HISAM,HDAM,HIDAM,VSAM IMS DB - an Hierarchical StructureDatabase Definitions - DBDProgram Specification Block ,Program Control Block DL/I Calls - Data Retrieval and ManipulationDL/I FunctionsQualified/ Unqualified Calls, SSAs, Command CodesDL/I Status codes

Basic TopicsHOME

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Advanced Topics

Data Sensitivity - Segment Level & Field levelCheckpoint & Restart IMS DB in CICS EnvironmentSecondary IndexingDifference between MPP, BMP, DLIUsing ‘HFCTDLI’

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File Vs Databases

Data more redundant Redundancy avoided Duplicate data Minimise Duplicates Data insecure Security provided No control over data Field level sensitivity Threat to Integrity Consistency of data Lack of inbuilt Data Logging, recovery features Commits & Rollbacks Lack of data Locks Automatic locks

HOMEDatabase Structures

Network Structures (e.g IDMS) Many to Many relationships Complex structure using Pointers Best for Keeping storageHierarchical Structures (e.g IMS DB) One to Many Relationships Inverted Tree like Structure Best for storing parent and child type entitiesRelational Structures (e.g DB2) One to Many, Many to One Best for ease of data retrieval

HOMEAccess Types

HSAM/SHSAM (Simple /Hierarchic sequential Access Method) The segments that make up the database record are related to one another by their physical locations (SHSAM has only root occurrences) HISAM/SHISAM (Simple / Hierarchic Indexed Sequential Access Method) The data is stored with hierarchic sequential organization along with an index for random processing (SHISAM has only index of root occurrences)

HDAM (Hierarchic Direct Access Method) The segment occurrences include prefixes that contain the direct address pointers to related segment - stores root segment occurrences HIDAM (Hierarchic Indexed Direct Access Method) Similar to HDAM but stores an index of the root segment occurrences

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IM S D B H ie ra rch ica l S tru c tu re

S R C SIn fo rm ationD a tab a se

S tra te rg ic B us in e ssU n its in fo

P ro je c t In fo

C lie n t In fo E m plo ye e d a ta

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P ro je c ts

C lie n ts

S a la ry

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S R C S u n its

HOMEBasic IMS Terminologies

SRCS Units

21

3

Clients Employ

Projects Salary

SegmentOccurrenceRoot SegmentParent SegmentChild SegmentSegment LevelPathDatabase RecordTwinsSequential ProcessingRandom Processing

SRCSInformationDatabase

Client Info

Project Info

HOMEDefinitions

Segment

- Unit of Information handled in IMS - Unit of data transferred from DL/I in an IO operation - Consists of fields, key fields & Search fields Occurrence - Specific segment of a particular type of segment - Contains actual user data Root Segment - Top of the hierarchy - All other segments are derived from the root Parent Segment - Segment that has dependent segments

HOMEDefinitions (contd) Child Segment - A dependent segment Segment Level - Depth of an IMS structure - Root is at Level 0, max 15 levels, max 255 segments Path - Series of segments from Root to the child Database record - Each occurrence of the Segment Plus all occurrence of the subordinate segments Twins - Segment occurrences of same type with same parent segment occurrence

HOMEIMS Control Blocks

IMS PGM1

IMSPGM2

DL/ICONTROL

UNIT

DBD1 DBD2 DBD3

PCB for DB1

PCB for DB2

PCB for DB3

PSB

DBDs

IMS DBsDB1 DB2 DB3

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DBD : Names the database and identifies the access method DBD Name = SRCS, ACCESS=(HIDAM,VSAM) DATASET : Specifies DD Name used in the JCL and other parameters DATASET DD1=DDSAT,DEVICE=3380,SIZE=(4096),FRSPC=(0,15) SEGM : Names the segment. Identifies the parent and establishes the length SEGM Name =SRU,PARENT=0,BYTES=40 LCHILD : Names the logical segment used in secondary Indexing and Logical database LCHILD NAME=(SRUNAME,SRCS1),PTR=INDX FIELD : Defines fields. And identifies search &key fields by SEQ parameter FIELD NAME=(SRUCODE,SEQ,U)BYTES=3,START=1,TYPE=C DBDGEN: Indicates the end of the DBDGEN process DBDGEN COMMENT: ‘*’ IN 3rd COLUMN for writing user comments

DBD : Database Description, describes physical DatabaseDBDGEN : DBDGEN Utility, Describes the physical structure of the Database and creates DBD

HOMESample DBD Listing for SRCS Info Database

DBD NAME=SRCS,ACCESS=(HIDAM,VSAM)DSG1 DATASET DD1=DDSAT,DEVICE=3380,SIZE=4096,FRSPC=0,15) SEGM NAME=SRU,PARENT=0,BYTES=40 FIELD NAME=(SRUCODE,SEQ,U),BYTES=3,START=1,TYPE=P FIELD NAME=SRUNAME,BYTES=5,START=4,TYPE=C FIELD NAME=SRULOC,BYTES=12,START=9,TYPE=C FIELD NAME=SRUHEAD,BYTES=20,START=21,TYPE=C SEGM NAME=CLIENT,PARENT=SRU,BYTES=45 FIELD NAME=(CLTID,SEQ,U),BYTES=4,START=1,TYPE=P FIELD NAME=CLTNAME,BYTES=10,START=5,TYPE=C FIELD NAME=CLTLOC,BYTES=11,START=15,TYPE=C FIELD NAME=CLTHEAD,BYTES=20,START=26,TYPE=C

HOMESEGM NAME=PROJECT,PARENT=CLIENT,BYTES=35 FIELD NAME=(PRJID,SEQ,U),BYTES=4,START=1,TYPE=P FIELD NAME=PRJNAME,BYTES=5,START=5,TYPE=C FIELD NAME=PRJTMSIZE,BYTES=4,START=10,TYPE=C FIELD NAME=PRJHEAD,BYTES=22,START=14,TYPE=CSEGM NAME=EMPLY,PARENT=SRU,BYTES=40 FIELD NAME=(EMPID,SEQ,U),BYTES=5,START=1,TYPE=P FIELD NAME=EMPNAME,BYTES=10,START=6,TYPE=C FIELD NAME=EMPPROJ,BYTES=5,START=16,TYPE=C FIELD NAME=EMPADDR,BYTES=20,START=21,TYPE=CSEGM NAME=SALARY,PARENT=EMPLY,BYTES=35 FIELD NAME=(SALEMPID,SEQ,U),BYTES=5,START=1,TYPE=P FIELD NAME=SALBASIC,BYTES=10,START=6,TYPE=C FIELD NAME=SALHRA,BYTES=5,START=16,TYPE=C FIELD NAME=SALDA,BYTES=5,START=21,TYPE=CDBDGENFINISHEND

HOMEPSB Program Specification Block,describes Logical structure of the Database that a program will use.It contains one or more PCB’s (Program Communication Block).PCB describes one Database.

PSBGEN PSBGEN Produces a load module stored in the PSBLIB library and creates PSB

Major Macros UsedPCB : Describes type (DB or DC), name of the DBD, Key length(length of the longest concatenated key the program can process) and processing Option (Defines how the segment may be accessed)PCB TYPE=DB,DBDNAME=SRCS,KEYLEN=20,PROCOPT=LSSENSEG : Define the name of the segments in the Database your program needs access toSENSEG NAME=CLIENT,PARENT=SRUSENFLD : Subordinate to the SENSEG macro, only fields that are defined by the SENFLD macro can be accessed from the I/O Area.SENFLD NAME=PROJECT,PARENT=CLIENTPSBGEN PSBNAME=MYPSB,LANG=COBOLEND

HOMESAMPLE PSB FOR SRCS INFO DB PROJECT REFERENCE PROGRAM

PCB TYPE=DB,DBDNAME=SRCS,KEYLEN=10,PROCOPT=LS SENSEG NAME=SRU,PARENT=0 SENSEG NAME=CLIENT,PARENT=SRU SENSEG NAME=PROJECT,PARENT=CLIENT PSBGEN PSBNAME=MYPSB,LANG=COBOL END

SAMPLE PSB FOR SRCS INFO DB PROJECT REFERENCE PROGRAM PCB TYPE=DB,DBDNAME=SRCS,KEYLEN=10,PROCOPT=LS SENSEG NAME=SRU,PARENT=0 SENSEG NAME=CLIENT,PARENT=SRU SENSEG NAME=PROJECT,PARENT=CLIENT SENSEG NAME=EMPLY,PARENT=SRU SENSEG NAME=SALARY,PARENT=EMPLY PSBGEN PSBNAME=MYPSB,LANG=COBOL END

HOMEDL/I INTERFACE

• DL/I passes control to your program• Uses ENRTY and CALL statement to code DL/I call in the Procedure Division

ENTRY ‘DLITCBL’ USING PCB-name1 PCB-name2 This DL/I tells entry of the program for Batch program & MPP program

CALL ‘CBLTDLI’ USING DLI-FUNCTION PCB-mask Segment-io-area [segment search arguments (s)]

This call is the name of the interface module that link edited with your program’s object module.

HOMECALL PARAMETERS

CALL ‘CBLDTLI’ USING DLI-FUNCTION PCB-mask Segment-io-area [segment search argument (s) ]

If we use PL/I language then CBLTDLI will be PLITDLI

Parameter Function

DL/I -Function A four byte code that tells DL/I what kind of call to makePCB-mask Arguments tells DL/I which PCB to use for the callIO-Area Tells DL/I where to put the segmentSSA Gives DL/I additional criteria to use in finding a particular Segment, Can be upto 15 SSA’s

HOMEDL/I FUNCTIONS

GU - Get Unique GN - Get Next GNP - Get Next within Parent GHU - Get Hold Unique GHN - Get Hold Next GHNP - Get Hold Next within Parent ISRT - To Insert REPL - To replace DLET - To Delete CHKP - To take a Checkpoint at a particular point XRST - To Restart from Particular point previous Checkpoint INIT - To Initialize SYNC - To commit

HOMEPCB MASK

Define in linkage Section and establishes correspondence between linkage Section PSB-mask and PSB’s with in your program.

SAMPLE PCB-MASK LAYOUT

VARIABLE DESCRIPTION

01 SRCS-PCB-MASK. 03 SR-DBD-NAME PIC X(8). Name of the Database being processed 03 SR-SEG-LEVEL PIC XX. Specifies current segment level in the DB 03 SR-STATUS-CODE PIC XX. Contains data yr program will evaluate after call 03 SR-PROC-OPT PIC X(4). Type of processing the program authorized to do 03 SR-SEG-NAME PIC X(8). Stores name of the segment just proceeded 03 SR-KEY-LENGTH PIC S9(5). Length of the concatenated key 03 SR-NUM-SENSEGS PIC S9(5). No of SENSEG macros subordinate to the PCB 03 SR-KEY-VALUE PIC X(20). Key value retrieved

HOMEI-O AREA LAYOUT FOR SEGMENTS

SRUCODE SRUNAME SRULOC SRUHEAD

01 SRU-AREA. 03 SRU-CODE PIC X(3). 03 SRU-NAME PIC X(5). 03 SRU-LOC PIC X(12) 03 SRU-HEAD PIC X(20).

CLTID CLTNAME CLTLOC CLT-HEAD

01 CLIENT-AREA. 03 CLT-CLTID PIC X(4). 03 CLT-CLTNAME PIC X(10). 03 CLT-CLTLOC PIC X(11) 03 CLT-CLTHEAD PIC X(20).

PROJID PRJNAME TMSIZE PRJADDR

01 PRJ-AREA. 03 PRJ-PROJID PIC X(4). 03 PRJ-PRJNAME PIC X(5). 03 PRJ-TMSIZE PIC X(4) 03 PRJ-HEAD PIC X(20).

EMPID EMPNAME EMPPROJ EMPADR

01 EMP-AREA. 03 EMP-ID PIC X(5). 03 EMP-NAME PIC X(10). 03 EMP-PROJ PIC X(5) 03 EMP-ADR PIC X(20).

01 SAL-AREA. 03 SAL-EMPID PIC X(5). 03 SAL-BASIC PIC X(10). 03 SAL-HRA PIC X(5). 03 SAL-DA PIC X(5).

EMPID BASIC HRA DA

HOMESEGMENT SEARCH ARGUMENT

• Identifies Segment Occurrence You want to access• You may have to code several SSA’s in a single DL/I CALL• There are two types of SSA’s Unqualified SSA & Qualified SSA

UNQUALIFIED QUALIFIED• Search for a Specific Segment type Searches for a specific occurrence of a specific segment type • Access the database Sequentially Access the database Randomly• Identify by segment name and space Identify by segment name and Seg-key

• Example01 UNSRU-SSA. 01 QUALKBU-SSA. 03 SRU-UNSSA-NM PIC X(8) Value ‘SRU ‘. 03 SEG-NAME PIC X(8) VALUE ‘SRU ‘. 03 FILLER PIC X Value Space. 03 COM-CODE PIC X(2) VALUE ‘*-’. 03 BEGIN-QUAL PIC X VALUE ‘(‘. 03 KEY-NAME PIC X(8) VALUE ‘SRUKEY’. 03 REL-OPR PIC X(2) VALUE ‘= ‘. 03 KEY-VALUE PIC X(20). 03 END-QUAL PIC X VALUE ‘)’.

HOMECOMMAND CODES

Command Code Description

D Retrieve Path F Access First Segment occurrence L Access Last Segment occurrence U Maintain current position at this level V Maintain current position at this level and higher levels Q Enqueue Segment N Do Not replace this Segment C Use a Concatenated Key P Establish Percentage at this level - Null command code / ignore

HOMEData Sensitivity

•DBA At a PSB level for SEGMENTS PROCOPT PCB TYPE=DB,DBDNAME-SRCS,,KEYLEN=11,PROCOPT SENSEG NAME =SRU,PARENT=0 SENSEG NAME =CLIENT,PARENT=SRU

Processing Options : G, I, R, D, A, P, O, N, T, E, L, GS, LS, H

At a PSB level for fields Done by DBA by use of SENFLD macro , specifying those fields that can be changed.

•Programmer At PROGRAM Level - Qualified SSA call with Command code N (No Replacement)

HOMECheckpointing & Restart• A point in the program where the database changes the program made are Considered complete and accurate -written to a DL/I log• Used for Recovery Process• Are of two types - Basic Checkpointing and Symbolic Checkpointing• Basic Checkpointing CALL ‘CBLTDLI’ USING DLI-CHKP, I-O-PCB-MASK, CHECKPOINT-ID.

• Symbolic Checkpointing Stores program data along with checkpoint records and retrieves that data when program restarts after failure. For extended Restart , an XRST call to be issued with the same fields as in CHKP call. It allows DL/I to retrieve the value in checkpoint record and restores the specified fields.

HOMEExplosive Mix - IMS DB with CICS

• Scheduling Call

CICS Region / Partition

User Task

User Interface Block(UIB)

Program Communication Block(PCB)

A DL/I task must establish addressability to UIB and one or more PCB

HOMEIMS & CICS Continued

CALL ‘CBLTDLI’ USING FUNC-INIT PSB-NAME ADDRESS OF DLIUIB

SET ADDRESS OF PCB-ADDR-LIST TO UIBPCBALSET ADDRESS OF PCB-1 TO PCB-1-ADRSET ADDRESS OF PCB-2 TO PCB-2-ADR…...

User Interface Block

Address of PCB List

Address of PCB 1

Address of PCB 2PCB Address list

PCB1

PCB2

HOMESecondary Indexing

Employee Index Database

EMP..Seg Addr

Employee ID

Index Pointer Segment

SRU

CLIENTS EMPLOYEE

PROJECTS

Index Source Segment

Index TargetSegment

Same index Source segment and index target segment

HOMESecondary Indexing Continued

Employee Index Database

SRU..Seg Addr

Employee ID

Index Pointer Segment

SRU

EMPLOYEE

Index Source Segment

Index TargetSegment

Different index Source segment and index target segment

CLIENTS

PROJECTS

HOMESecondary Indexing Continued

• Alternate sequencing is provided by storing pointers to Segments of the indexed Database in a separate secondary index data base

• Secondary index data base has only one segment type - the Index pointer segment which in turn contains a prefix element and a data element

• Prefix element points to the index target segment

• Secondary indexing is useful for accessing segments were both

Index source segment and index target segment are same Index source segment and index target segment are different

• Two DBDGENS are required as a secondary database involves two database: one for indexed database , the other for the secondary index database

HOMESecondary Indexing Continued

DBDGEN - The Secondary Index code for SRCS DB

DBD NAME=SRCS,ACCESS=(HIDAM,VSAM)DSG1 DATASET DD1=DDSAT,DEVICE=3380,SIZE=4096,FRSPC=0,15) SEGM NAME=SRU,PARENT=0,BYTES=40 FIELD NAME=(SRUCD,SEQ,U),BYTES=2,START=1,TYPE=P …… SEGM NAME=EMPLY,PARENT=SRU,BYTES=80 LCHILD NAME= (MYPNTR,MYDBD),POINTER=INDX FIELD NAME=(EMPID,SEQ,U),BYTES=5,START=1,TYPE=P XDFLD NAME=MYINDX,SRCH=EMPID FIELD NAME=EMPNAME,BYTES=25,START=6,TYPE=C FIELD NAME=EMPPROJ,BYTES=15,START=31,TYPE=C FIELD NAME=EMPADDR,BYTES=35,START=46,TYPE=C …….

HOMESecondary Indexing Continued

DBDGEN - The Secondary Index code for Secondary Index DB

DBD NAME=MYIDBD,ACCESS=(INDEX)DSG1 DATASET DD1=DDKAY,DEVICE=3380,SIZE=4096,FRSPC=0,15) SEGM NAME=MYPNTR,PARENT=0,BYTES=6 LCHILD NAME= (EMPID,SRCS), INDX=MYINDX FIELD NAME=(MYEMPID,SEQ,U),BYTES=6,START=1,TYPE=CDBDGENFINISHEND

PSB Requirements for Secondary Indexing. PCB TYPE=DB,DBDNAME=SRCS,KEYLEN=10,PROCOPT=LS, PROCSEQ=MYIDBD SENSEG NAME=EMPLY SENSEG NAME=SRU,PARENT=EMPLY PSBGEN PSBNAME=MYSBX,LANG=COBOL END

HOMEDifference Between MPP , BMP & DLI

• MPP (Message Processing Program) For Online programs( IMSDC) only. PSB used by a MPP program cannot be used by another programs simultaneously. Cannot run on Individual partitions.

• BMP (Batch message processing) For batch programs only PSB used by a BMP program cannot be used by another programs simultaneously. All partitions specified in PSB will be allocated whether used by program or not. Cannot run on Individual partitions. • DL/I It can be used as Interface between MPP and Database OR BMP and Database For batch DL/I job it can access database directly PSB of DL/I job can be used by another jobs simultaneously It can run on Individual partitions.

Prepared By

Mahesh Eluru

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