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IMS-DB Information Management System DB Concepts & Programming

HOME. IMS-DB Information Management System DB Concepts & Programming. www.geocities.com/srcsinc. HOME. Basic Topics. Files Vs Databases Networked,Hierarchical & Relational structure Access types - HSAM, HISAM,HDAM,HIDAM,VSAM IMS DB - an Hierarchical Structure Database Definitions - DBD

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IMS-DB Information Management System DB Concepts & Programming

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  1. HOME IMS-DBInformation Management SystemDB Concepts & Programming www.geocities.com/srcsinc

  2. HOME Basic Topics • Files Vs Databases • Networked,Hierarchical & Relational structure • Access types - HSAM, HISAM,HDAM,HIDAM,VSAM • IMS DB - an Hierarchical Structure • Database Definitions - DBD • Program Specification Block ,Program Control Block • DL/I Calls - Data Retrieval and Manipulation • DL/I Functions • Qualified/ Unqualified Calls, SSAs, Command Codes • DL/I Status codes

  3. HOME Advanced Topics • Data Sensitivity - Segment Level & Field level • Checkpoint & Restart • IMS DB in CICS Environment • Secondary Indexing • Difference between MPP, BMP, DLI • Using ‘HFCTDLI’

  4. 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

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

  6. Access 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

  7. Basic IMS Terminologies 3 2 1 SRCS Units SRCS Information Database Segment Occurrence Root Segment Parent Segment Child Segment Segment Level Path Database Record Twins Sequential Processing Random Processing Clients Employ Client Info Projects Salary Project Info

  8. Definitions • 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

  9. Definitions (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

  10. IMS Control Blocks PCB for DB1 IMS PGM1 IMS PGM2 PSB PCB for DB2 PCB for DB3 DBDs DBD1 DBD2 DBD3 DL/I CONTROL UNIT IMS DBs DB1 DB2 DB3

  11. DBD : Database Description, describes physical Database DBDGEN : DBDGEN Utility, Describes the physical structure of the Database and creates DBD • 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

  12. Sample 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

  13. SEGM 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=C SEGM 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=C SEGM 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=C DBDGEN FINISH END

  14. PSB 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 Used PCB : 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=LS SENSEG : Define the name of the segments in the Database your program needs access to SENSEG NAME=CLIENT,PARENT=SRU SENFLD : 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=CLIENT PSBGEN PSBNAME=MYPSB,LANG=COBOL END

  15. 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 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

  16. DL/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.

  17. CALL 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 make PCB-mask Arguments tells DL/I which PCB to use for the call IO-Area Tells DL/I where to put the segment SSA Gives DL/I additional criteria to use in finding a particular Segment, Can be upto 15 SSA’s

  18. DL/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

  19. PCB 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

  20. I-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). 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). 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). EMPID BASIC HRA DA 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). PRJNAME TMSIZE PRJADDR PROJID 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).

  21. SEGMENT 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 • Example • 01 UNSRU-SSA. 01 QUALKBU-SSA. • 03 SRU-UNSSA-NM PIC X(8) Value ‘SRU ‘. 03 SEG-NAMEPIC 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 ‘)’.

  22. COMMAND CODES Command CodeDescription 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

  23. Data 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)

  24. Checkpointing & 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.

  25. Explosive Mix - IMS DB with CICS • Scheduling Call • CICS Region / Partition User Interface Block (UIB) User Task Program Communication Block (PCB) A DL/I task must establish addressability to UIB and one or more PCB

  26. IMS & CICS Continued CALL ‘CBLTDLI’ USING FUNC-INIT PSB-NAME ADDRESS OF DLIUIB SET ADDRESS OF PCB-ADDR-LIST TO UIBPCBAL SET ADDRESS OF PCB-1 TO PCB-1-ADR SET ADDRESS OF PCB-2 TO PCB-2-ADR …... User Interface Block Address of PCB List Address of PCB 1 PCB Address list Address of PCB 2 PCB1 PCB2

  27. Secondary Indexing Employee Index Database EMP..Seg Addr Employee ID SRU Index Target Segment Index Pointer Segment Index Source Segment CLIENTS EMPLOYEE PROJECTS Same index Source segment and index target segment

  28. Secondary Indexing Continued Employee Index Database SRU..Seg Addr Employee ID SRU Index Target Segment Index Pointer Segment Index Source Segment CLIENTS EMPLOYEE PROJECTS Different index Source segment and index target segment

  29. Secondary 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

  30. Secondary 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 …….

  31. Secondary 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=C DBDGEN FINISH END 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

  32. Difference 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.

  33. HOME A TUTORIAL Prepared By Mahesh Eluru from www.geocities.com/srcsinc

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