Post on 03-Jan-2016
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Information Management System DB Concepts & Programming
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
Basic Topics
Advanced Topics
Data Sensitivity - Segment Level & Field level
Checkpoint & Restart
IMS DB in CICS Environment
Secondary Indexing
Difference between MPP, BMP, DLI
Using ‘HFCTDLI’
File Vs Databases
Data more redundant Redundancy avoided
Duplicate data Minimize 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
Database 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
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
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
E m p loye e S a la ryD e ta ils
P ro je c ts
C lie n ts
S a la ry
E m p loy
S R C S u n its
Basic IMS Terminologies
SRCS Units
21
3
Clients Employ
Projects Salary
Root SegmentParent SegmentChild SegmentSegment LevelSegment OccurrencePathDatabase RecordTwinsSequential ProcessingRandom Processing
SRCSInformationDatabase
Client Info
Project Info
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
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
IMS 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
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
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
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=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
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 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
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
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.
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 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
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
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
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).
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
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
• 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 ‘)’.
COMMAND 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
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)
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.
Explosive 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
IMS & 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
Secondary 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
Secondary 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
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
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 …….
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=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
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.