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IMS DC
IMS DC Slide: 1
Pre-Requisite: IMS DB knowledge
An Introduction
IMS DC Slide: 2
• IMS: Which is a Hierarchical DBMS, supplied by IBM & runs on Mainframe Computers. It has 2 main components:Data Base (DB) Processing Data Communication (DC) Processing.
Note: DL/I DOS/VS does not support Data Communication Component.
Interactive Programs
IMS DC Slide: 3
• Major Kinds of Online Programs that can be written:
– Inquiry Programs– Data Entry Programs– Maintenance Programs– Menu Programs
COMPARISON BETWEEN ONLINE AND BATCH PROGRAMS
IMS DC Slide: 4
BATCH ONLINE
Pre-Determined Scheduling Intervals
Arbitrary Scheduling by Users
Necessary creation of Input Files
Processing of Data as it occurs
Lack of Access to current Data Data up-to-date and current and available for Inquiry
Delay in Processing Erroneous Data
Immediate error correction
Databases cannot be shared with other updating programs
Database can be shared with other updating programs
Software Components of an IMS DC system
Data base & datasets
CommunicationControl
Editing Modules(MFS)
Queue ManagerQPOOL
Message Queue Overflowdatasets
VTAM Terminals
MVS addressSpace
VTAM
Non VTAMTerminals
MVS Address space
IMS / VS controlregion
Logging
DLI
MVS addressSpace
MPP region
MVS addressSpace
MPP region
MVS addressSpace
MPP region
MVS addressSpace
BMP region
Logging data sets
VTAM Terminals
IMS DC Slide: 5
IMS-DC OFFERS:
IMS DC Slide: 6
1. A way to improve customer and internal service by providingcurrent and consistent information
2. A way to interact with users with critical response times
3. A way to distribute processing function to different locations
4. A way to improve productivity for online applications
Features of IMS:
IMS DC Slide: 7
1. Manages IMS-DC Terminal Network
2. Routes Messages for various destinations
3. Scheduling of messages
4. Manages resources allocated to IMS
5. Provides restart, recovery facilities
6. Interacts with Databases for data retrieval and updation
ELEMENTS OF AN IMS-DC ONLINE SYSTEM
TERMINALS
MESSAGES
REGIONS
PROGRAMS
DATABASES
IMS CONTROL BLOCKS
IMS LOGS
IMS DC Slide: 8
IMS STANDS BETWEEN THE TERMINAL AND THE APPLICATION PROGRAM
TERMINAL
DATABASE
IMS
INPUTMESSAGE
OUTPUTMESSAGE
INPUTMESSAGE
OUTPUTMESSAGE
PROCESS
IMS DCPROGRAM
IMS DC Slide: 9
IMS DC
IMS DC Slide: 10
• DC handles information in the form of messages that flow between remote terminals and application programs.
• Programs & Databases that will run under the control of IMS must be defined in the IMS system definition.
• Two main Categories of Resources:Application Resources & Data communication Resources
• Types of IMS DC Application Programs:BMP: Batch Message Processing, Scheduled by System operatorMPP: Message Processing Program, scheduled by IMS
IMS DC Slide: 11
• IMS/VS forms a layer in between the Terminal and the IMS-DC programs, this helps in asynchronous mode of communication. This type of program is called Message Processing Programs(MPPs)
• Message - is a unit of Data that gets transmitted between a program and a Terminal
• Primary Inputs to and outputs from DC programs are messages.• For each Input message, DC program does predictable
processing against its databases and sends an output message that to User’s screen.
How IMS uses MVS regions
IMS DC Slide: 12
Regions in IMS.
IMS/VS CONTROL REGION
TERMINAL TERMINAL
LOG DATASETS
MPPREGION
MPPREGION
MPPREGIONBMP
REGION
DATABASE DATASETS
Control Region
IMS DC Slide: 13
– The main function of this region is that, all terminal, Database, and Logging Operations associated with IMS-DC programs are performed through this Region.
MPP Region
IMS DC Slide: 14
• MPP Region
– is where IMS schedules & executes Message Processing Programs.
– The Number of MPP Regions determines the number of MPPs that can be active at any one time.
– A program that occupies an MPP Region runs until it has processed all of the input messages that IMS has received for it. Then it ends, and the MPP region in which it was running is freed and made available for another Application Program.
Batch Message Program
IMS DC Slide: 15
• BMP (Batch Message Processing) Region
– A BMP program is much like MPP, except that the terminal response is not required for each input Message. The Database Processing and input message requires does not have to be done immediately.
– These are typically Batch Programs.– The main Advantage is, it can access Data Bases
that are allocated to the IMS Control Region, for use by MPPs at the same time.
Terminals & Security under IMS
IMS DC Slide: 16
• LTERM: For Application Functions, IMS uses logical terminal names rather than Physical names. Note: Within IMS, each LTERM name is associated with one and only one physical terminal. Ex: LDPAYR01
• LTERM names are limited to 8 chars• Master Terminal
Terminals & Security under IMS
IMS DC Slide: 17
• SMU Security Maintenance UtilityRACF Resource Allocation & Control Facility
• Transaction Security
• SIGN ON verification
• LTERM security
How IMS Manages Input messages
IMS DC Slide: 18
• Three kinds of IMS input messages:a. Transactionsb. Terminal to Terminal messagec. IMS commands
• IMS uses first 8 bytes of an input message to identify the message’s type.
• How IMS handles the three kinds of Input messages ??? • Input message Editing
Input Message Editing
IMS DC Slide: 19
• Two types of common Editing :
IMS basic edit: Remove communication control characters from input message and add them to output messages.
Message Format Service edit: Provides more extensive editing functions.
MFS builds the input message that the application program will receive. Part of building that message, it can insert the eight character transaction code at the beginning of the message.
How IMS supports an Application Program
IMS DC Slide: 20
After editing, IMS has to store the transaction temporarily.
Queue manager stores the transactions in the message queue, QPOOL.
If multiple transaction types are queued but too few dependent regions are available for all of them, IMS makes scheduling decisions.
IMS DC & CICS
IMS DC Slide: 21
• Many users are running an application, the IMS system funnels all of their messages through one program.
• CICS treats each user separately, it treats each terminal user separately.
• Many users are entering data of the same program, all the messages they enter are routed to same application program by IMS. IMS Keeps track of where each message came from and where each output message should go.
IMS DC Slide: 22
IMS-DC Processing
Programming Elements for IMS-DC Processing
– DL/I Calls for DC Operation– PCB mask for DC Operation– Message Handling.
DL/I calls for DC operations
IMS DC Slide: 23
• Basic unit of I/O for data communication DL/I call is segment• Most messages consist of just one segment occurrence, some
may contain multiple segments.• Message segments are not arranged hierarchically, they just
represent parts of a message.
•A Data Base Call
•CALL ‘CBLTDLI’ USING
DLI-GU
DB-PCB-MASK
RSEGMENT
INV-SSA.
•A Data communication Call
•CALL ‘CBLTDLI’ USING
DLI-GU
IO-PCB-MASK
RSEGMENT.
DL/I calls for DC Operation
IMS DC Slide: 24
• CALL ‘CBLTDLI’ USING DLI-GU IO-PCB-MASKINPUT-MESSAGE-SEG.
• First argument is the Function Code• GU: Issue a GU call to retrieve the first segment of an Input
Message. • GN is issued to retrieve the subsequent Messages. • ISRT call is issued for each segment, to send an Output
Message.
PCB Mask for DC operation
IMS DC Slide: 25
• A DC call must specify a Linkage Section PCB Mask, which is a special one that’s just for Message Processing. It’s called I/O PCB.
• To provide address to this PCB, the program must name its Linkage section mask definition on the ENTRY statement at the beginning of the Procedure Division.
• I/O PCB must be the first PCB listed on the ENTRY statement.• Format of a I/O PCB is different from a data base PCB’s format.
Cobol Code for an I/O PCB mask.
IMS DC Slide: 26
• 01 IO-PCB-MASK.05 IO-PCB-LOGICAL-TERMINAL PIC X(8).05 FILLER PIC X(2).05 IO-PCB-STATUS-CODE PIC X(2).05 IO-PCB-DATE PIC S9(7) COMP-305 IO-PCB-TIME PIC S9(6)V9 COMP-305 IO-PCB-MSG-SEGMENT-NUMBER PIC S9(5) COMP.05 IO-PCB-MOD-NAME PIC X(8).05 IO-PCB-USER-ID PIC X(8).
Message Handling
IMS DC Slide: 27
– When GU or GN calls been issued to retrieve an Input Message Segment, DL/I places the Message Segment data in the specified I/O Area.
– When ISRT call is issued to send an output Message Segment, DL/I gets the Data from the specified I/O Area.
Retrieving an Input Message
IMS DC Slide: 28
• Application Program issues either a Single ‘GU’ call or a ‘GU’ call followed by one or more ‘GN’ calls.
• To retrieve single segment input message, One ‘GU’ call need to be issued. When the Program gets ‘QC’ status code ( Instead of Blanks), it should be noted that there is No messages in the Queue.
• To retrieve Multiple segment input Messages, need to issue ‘GU’ call first to retrieve the first Segment. Then, to retrieve subsequent message segments for that Message, it issues ‘GN’ calls repeatedly until ‘QD’ status code is encountered.
Send an Output Message
IMS DC Slide: 29
• Issue ISRT calls that specify the I/O PCB.
• The Program issues a separate ISRT calls for each segment (for Multiple Segments) to be written.
• I/O Area to be build before you issue this call
Input Message I/O Area Format
IMS DC Slide: 30
ZZ
LL Data
•LL – Length of Entire Segment Usage: S9(3) Comp
•ZZ – IMS Reserved Data Usage: S9(3) Comp
• Input Message I/O Area Format
Output Message I/O Area Format
Z1
LL Data
•LL – Length of Entire Segment Usage: S9(3) Comp
•Z1 & Z2 – IMS Reserved Data Usage: X(2)
Z2
IMS DC Slide: 31
COBOL PROGRAM -
IDENTIFICATION DIVISION.PROGRAM-ID. PGM01.ENVIRONMENT DIVISION.DATA DIVISION.WORKING-STORAGE SECTION.01 SWITCHES.
05 END-OF-MESSAGES-SW PIC X VALUE 'N'.88 END-OF-MESSAGES VALUE 'Y'.
01 INPUT-MESSAGE-IO-AREA.05 IN-LL PIC S9(3) COMP.05 IN-ZZ PIC S9(3) COMP.05 IN-TRAN-CODE PIC X(8).05 IN-INVNO PIC X(6).
01 O-TEMP PIC X(2000).
01 OUTPUT-MESSAGE-IO-AREA.05 OP-LL PIC S9(3) COMP-3 VALUE +14C.05 OP-ZZ PIC S9(3) COMP-3 VALUE ZERO.05 OP-INVNO PIC X(6).05 OP-STAX PIC 9(4).
IMS DC Slide: 32
01 DLI-FUNCTIONS.05 DLI-GU PIC X(4) VALUE 'GU '.05 DLI-ISRT PIC X(4) VALUE 'ISRT'.
01 RECEIVABLE-SEGMENT.05 R-INVOICE-NUMBER PIC X(6).05 R-INVOICE-DATE PIC X(6).05 R-PO-NUMBER PIC X(6).05 R-STAX PIC 9(4).
01 INVOICE-NO-SSA.05 FILLER PIC X(9) VALUE 'RECEISEG('.05 FILLER PIC X(10) VALUE 'RECEINVN ='.05 INVOICE-NO-SSA-VALUE PIC X(6).05 FILLER PIC X VALUE ')'.
01 MFS-MOD-NAME PIC X(8) VALUE 'MFSO '.
IMS DC Slide: 33
LINKAGE SECTION.
01 IO-PCB-MASK.05 IO-PCB-LOGICAL-TERM PIC X(8).05 FILLER PIC X(2).05 IO-PCB-STATUS-CODE PIC X(2).05 IO-PCB-DATE PIC S9(7) COMP-3.05 IO-PCB-TIME PIC S9(6)V9 COMP-3.05 IO-PCB-MSG-SEQ-NUMBER PIC S9(5) COMP.05 IO-PCB-MOD-NAME PIC X(8).05 IO-PCB-USER-ID PIC X(8).
*01 CR-PCB-MASK.
05 CR-PCB-DBD-NAME PIC X(8).05 CR-PCB-SEGMENT-LEVEL PIC XX.05 CR-PCB-STATUS-CODE PIC XX.05 CR-PCB-PROC-OPTIONS PIC X(4).05 FILLER PIC S9(5) COMP.05 CR-PCB-SEGMENT-NAME PIC X(8).05 CR-PCB-KEY-LENGTH PIC S9(5) COMP.05 CR-PCB-NUMB-SENS-SEGS PIC S9(5) COMP.05 CR-PCB-KEY PIC X(22).
IMS DC Slide: 34
PROCEDURE DIVISION.ENTRY 'DLITCBL' USING IO-PCB-MASK CR-PCB-MASK.
PERFORM 100-PROCESS UNTIL END-OF-MESSAGES.GOBACK.
100-PROCESS.PERFORM 110-GET-INPUT-MESSAGE.IF NOT END-OF-MESSAGES
PERFORM 120-GET-INVOICE-DATAPERFORM 150-INSERT-OUTPUT-SEGMENT.
110-GET-INPUT-MESSAGE.CALL 'CBLTDLI' USING DLI-GU
IO-PCB-MASKINPUT-MESSAGE-IO-AREA.
IF IO-PCB-STATUS-CODE = 'QC'MOVE 'Y' TO END-OF-MESSAGES-SW.
IMS DC Slide: 35
120-GET-INVOICE-DATA.MOVE IN-INVNO TO INVOICE-NO-SSA-VALUE.CALL 'CBLTDLI' USING DLI-GU
CR-PCB-MASKRECEIVABLE-SEGMENTINVOICE-NO-SSA.
IF CR-PCB-STATUS-CODE NOT = SPACEMOVE '9999' TO OP-STAX
ELSEMOVE R-INVOICE-NUMBER TO OP-INVNOMOVE R-STAX TO OP-STAX.
150-INSERT-OUTPUT-SEGMENT.CALL 'CBLTDLI' USING DLI-ISRT
IO-PCB-MASKOUTPUT-MESSAGE-IO-AREAMFS-MOD-NAME.
IMS DC Slide: 36
Message Format Services
IMS DC Slide: 37
• What is MFS?• Control Blocks• Format Set
– MFS, is an IMS feature that lets you use Formatted Display Screens.
– MFS Modules reside in the IMS Control Region, and they are invoked between IMS Communication Control Module and its Queue Manager.
– MFS can reduce system resources an application uses
MFS Control Blocks
IMS DC Slide: 38
Terminal
Device InputFormat (DIF)
Device OutputFormat (DOF)
Mesg InputDescriptor(MID)
Mesg OutputDescriptor(MOD)
Application Program
Input Message
Sent by Terminal
Output Message
Sent by Program
Output MessageRecv by Terminal
Input MessageRecv by Program
• To process a Transaction, MFS uses 4 Control Blocks.
DIF & MID
IMS DC Slide: 39
– For an Input Message, MFS uses a block called a Device Input Format (DIF) to interpret data as it’s received from a Terminal.
– It uses second Block called Message Input Descriptor (MID), to determine how that input Data should be formatted for presentation to the Application Program.
IMS DC Slide: 40
– For an Output Message, MFS uses similar blocks, a Message Output Descriptor (MOD) is used to interpret Data Received from the Application Program.
– A Device Output Format (DOF), is used to determine how that Data should be formatted for Transmission to the Terminal.
Format Set
IMS DC Slide: 41
• MFS control statements– MFS control statements are often referred as Format Set.
• Format Set:– Defines the way screens to be used in application will look.– Defines format of input & output messages.– Specifies the relationship between data on the screen and
data in a message. • MFS Language Utility is used to Translate the Format Sets to
the Control Blocks.
• /Format <MOD name>
Format of an MFS Control Statement
IMS DC Slide: 42
• COLS • 1 - 8 Label• 10 - 14 Operation• 16 - 71 Operand• 72 Continuation Char
• Three Groups of MFS Statements:Device Format Control StatementsMessage descriptor control statementsCompilation Control Statements
Define a Screen in Format Set
IMS DC Slide: 43
• One set of Control statements for both - for a 3270 same screen format must be used for both input & Output
• One Set of Control statements for both DIF & DOF• Device Format begins with FMT & ends with FMTEND• FMT
DEVDIV
DPAGEDFLDDFLD
DPAGEFMTEND
FMT
IMS DC Slide: 44
• FMT: Identifies the beginning of a device format• FMTEND: Control statements end with a FMTEND statement• No parameters• Appropriate Label on FMT• Label coded on FMT statement can be no more than six
characters long.
Format Set
IMS DC Slide: 45
INQDF FMTDEV TYPE=(3270,2),FEAT=IGNORE,DSCA=X’OOAO’DIV TYPE=INOUTDPAGE CURSOR=((1,2))
TRANINV DFLD POS=(1,2),LTH=15OUTTEXT DFLD POS=(3,2),LTH=702
FMTENDINQO MSG TYPE=OUTPUT,SOR=(INQDF,IGNORE),NXT=INQI
SEGMFLD OUTTEXT,LTH=702MSGEND
INQI MSG TYPE=INPUT,SOR=(INQDF,IGNORE),NXT=INQOSEGMFLD TRANINV,LTH=15MSGENDEND
DEV Control Statement
IMS DC Slide: 46
• PFKDF FMTDEV TYPE=(3270,1)
FEAT = IGNOREPFK=(PFKTEXT,1=‘01’,2=‘02’,8=‘08’)
FMTEND
PFKEXI MSG TYPE=INPUT,SOR=(PFKDF,IGNORE),NXT=PFKDFO
SEGMFLD PFKTEXT,
LTH=2MSGEND
DEV
IMS DC Slide: 47
• TYPE: Specify the device models for which device format blocks should be created.
• DSCA: To specify a default terminal action that’s performed when an output message is sent to a 3270 device.Ex: DSCA=X’00A0’ causes unprotected fields on the screen to be erased before the output message is displayed.
• SYSMSG: Names a device field in which messages that come to the terminal from IMS will be displayed.
• DPAGE: Primary Function Handle Multiple logical pages Secondary Function: Initial Cursor positioning & Field Fill
Program Function Keys (PFKeys)
IMS DC Slide: 48
• PFK parameter specifies how MFS should support program function keys.
• First Part: Target input message field• Second Part: Keyword / positional format
• Positional:PFK=(PFKTEXT,‘01’,‘02’,,,,,,‘08’)
DEV TYPE= (3270,1)(3270,2)3270-An
,FEAT=IGNORE[,PFK=(pfkeyfield,[integer=] ‘literal’
NEXTPPNEXTMSGP [,…])]ENDMPP1
IMS DC Slide: 49
DPAGE
IMS DC Slide: 50
• Label DPAGE [CURSOR=(LINE,COL,CFIELD)…][FILL=fillchar][MULT=Yes]
• FILL: The fill character to be used for output device fields.Ex: PT, C’c’, X’hh’
• MULT: Multiple physical pages within device page can be used to generate an input message.
DFLD
IMS DC Slide: 51
• Specifies where on the screen a field is located & how large thefield is.
• Need to code a label only when the device field it defines are to be related with a input, output or both.
• LTH : Not to be coded for a Literal in a device field • DFLD ‘ABC Company Services’,
POS=(1,2),ATTR=(HI,PROT)
• CURDATE DFLD POS=(1,72),LTH=8ATTR=(HI,PROT)
DFLD Statement
IMS DC Slide: 52
• ATTR: Field Characteristics• Default Protection attribute for a non-literal field is unprotected• Label DFLD ‘literal’,
POS=(1,1),LTH=20,ATTR=ALPHA
• ATTR=• ALPHA / NUM• NOPROT/PROT• NORM/NODISP/HI• NOMOD/MOD
Modified Data Tags
IMS DC Slide: 53
• MDT tag indicates whether or not the data in the field has been changed by the terminal user since the screen was sent to the device.
• When a screen is displayed, MDT’s of fields is OFF.• Advantage: Telecommunications Efficiency
Define Messages in a Format Set
IMS DC Slide: 54
• Code separate sets of control statements to define a MID and a MOD.
• Begin with a MSG & end with a MSGEND.• MOD: TYPE=OUTPUT• MID: TYPE=INPUT• Must code a label on the MSG statement.• Message Fields: MFLD• LTH=55 (LL & ZZ fields that are defined in the segment I/O
areas need not be included in the message description in the format set.
Message Descriptor Control Statements
IMS DC Slide: 55
• MSGLPAGE
PASSWORDMFLD
SEGMFLDMFLD
LPAGESEG
MFLDMSGEND
MSG
IMS DC Slide: 56
• msgname MSG TYPE=(INPUT / OUTPUT ) SOR =(dfname,IGNORE)NXT=nextmsgnamePAGE=YES
MSGEND• SOR: Parameter on each MSG statement. Code the name of the
device format (FMT statement label) that is associated with the message this group of statements define.
• NXT: Parameter specifies the message descriptor MFS that will be used. MSG that defines a MID you code a MOD and for MOD you code the MID label.
MFLD Control Statement
IMS DC Slide: 57
• MFLD {SOURCE / DESTINATION }LTH = LengthJUST={L / R}FILL=fillcharATTR=(YES)
• Input Message Field Descriptor:-MFLD ‘DI2 ‘, LTH=8MFLD INVNO,LTH=6MFLD (INVNO,’000000’),LTH=6• Output Message field:-
MFLD (CURDATE,DATE2)
JUST, FILL, ATTR parameter in MFLD Statement
IMS DC Slide: 58
• JUST parameter specifies how data should be positioned in a message field.
• Default is Left Justification
• FILL parameter specifies what pad character MFS should use to complete a field when the data that’s mapped into it doesn’t fill. you with Ex: FILL=C’0’
FILL=X’ ‘FILL=NULL
• ATTR = YES specifies that an application program can dynamically change the attributes set in the Device field.
Compilation Control Statements
IMS DC Slide: 59
• PRINT ON,NOGEN• PRINT OFF• END• EJECT• COPY • symbol EQU ‘literal’
APA EQU ‘ATTR=(PROT,ALPHA)’SUBTOTAL DFLD POS=(3,55),LTH=9,APA
IMS DC Slide: 60
• By default : Same MOD to be used for an output message that was used for the previous entry.
• Complex Screen Flows: • When output formats are changed, when 2 or more screen
displays are used.
IMS DC Slide: 61
• Format of the ISRT call with the MOD name segmentCALL ‘CBLTDLI’ USING DLI-ISRT
IO-PCB-MASKOUTPUT-MESSAGE-IO-AREAMFS-MOD-NAME.
MFS-MOD-NAME is a working storage field defined with PIC X(8).
• How to Control screen flows from within MFS ?Easy to control screen flows from within an application without involving application program. Provide a way for the operator tocause an input message that begins with:/format mod-name
Screen Example
IMS DC Slide: 62
• Receivables Menu Date: xxxxxxx
PF1 Enter Cash ReceiptsPF2 Display Invoice Summary
Format Set for Menu Program
IMS DC Slide: 63
• MENUDF FMTDEV TYPE=(3270,2),FEAT=IGNORE,SYSMSG=ERRMSG,
PFK=(PFKFIELD,’/FOR CRO ‘,’/FOR DI2O ‘,’/FOR DIDSO’)DIV TYPE=INPUTDFLD ‘Receivables Menu’,POS=(1,2),ATTR=(PROT,ALPHA,HI,NOMOD)DFLD ‘Date’,POS=(1,65),ATTR=(PROT,ALPHA,HI,NOMOD)
CURDATE DFLD POS=(1,72),LTH=9,ATTR=(PROT,ALPHA,HI,NOMOD)…………………………………...
ERRMSG DFLD POS(23,2),LTH=79,ATTR=(PROT,ALPHA,NORM,NOMOD)FMTEND
MENUI MSG TYPE=INPUT,SOR=(MENUDF,IGNORE),NXT=MENUOSEGMFLD PFKFIELD,LTH=10MSGEND
MENUO MSG TYPE=OUT,SOR=(MENUDF,IGNORE),NXT=MENUISEGMFLD (CURDATE,DATE2)MFLD LTH=1MSGEND
IMS DC Slide: 64
• Field attributes values set with ATTR parameter of DFLD statement and CURSOR parameter of the DPAGE statement could be dynamically changed.
• Used to call attention to data entry errors.• Steps:-• Identify fields that are eligible for dynamic field attribute
modifications by setting ATTR = YES in MFLD statement.
Identifying the Output Message Fields
IMS DC Slide: 65
• Steps:-• Identify fields that are eligible for dynamic field attribute
modifications by setting ATTR = YES in MFLD statement.• 2 bytes of MFLD will contain control information that specifies
what the overriding attributes will be.• Increase the LTH of the Message Field by 2.• MFLD INVNO,LTH=8,ATTR=YES• Two bytes prefix is packed with information.• First byte is cursor control. If cursor positioning is not required
all the bits in the first control byte should be 0000 0000. (LowValues)
Specify Field Attributes overrides from a Program
IMS DC Slide: 66
05 OM-INVOICE-NO.10 OM-INVOICE-NO-PREFIX.
15 OM-INVOICE-NO-CURSOR PIC X VALUE LOW-VALUE.15 OM-INVOICE-NO-ATTR PIC X.
10 OM-INVOICE-NO-DATA PIC X(6).
• Ex: A common function is changing fields intensity from normal to bright without changing other attributes. 1000 0000 is required in second byte.
• 05 ATTR-CHANGE-TO-BRIGHT PIC X VALUE ‘h’.• Setting a fields default attribute: 1000 0000, hex 80
05 ATTR-RESET-TO-DEFAULT PIC X VALUE ‘ ‘.• To mark a field with error,
MOVE ATTR-CHANGE-TO-BRIGHT TO OM-INVOICE-NO-ATTR
Cursor & Attribute ControlFirst byte (Cursor Control) Second Byte (Attribute Control)
0 0 0 0 0 0 1 0Bit 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
CursorPositioning
Shift Intensity Pen MDT
ProtectionAttribute Override
Byte
Bits Function Values
1 0-1 Cursor Pos. 00 Cursor Positioning not requested11 Position cursor at this field. (Values 01 and 10 are invalid)
2-7 000000 (Always)2 0 1 (Always)
1 AttributeOverride Type
0 Use the attr. Specifications that follow to activate only specifiedattributes (that is attributes whose corresponding override bit is on
1 Use the attribute specs that follow to replace all device field attribu2 Protect. Attr. 0 Unprotected
1 Protected3 Shift Attribute 0 Alphanumeric Shift
1 Numeric Shift4-5 Intensity Attrib 00 Normal Intensity
01 No-display10 Bright Intensity11 Bright Intensity
6 Light-pen Attr 0 Should be 0 for non- Light – Pen applications7 MDT 0 MDT off
1 MDT on
IMS DC Slide: 67
Control the cursor
IMS DC Slide: 68
• Two type we can position the cursor from an application Program:Field Oriented Cursor control Absolute Cursor Control
• Field Oriented CursorTo require cursor positioning at a field, move the left brace hex value, hex C0, binary 1100 0000 to the first of the two control bytes. Don’t want Cursor positioning at a field, first byte of the prefix should contain Low-Value.
Absolute Cursor Control
IMS DC Slide: 69
• Program specifies the exact column & line position where the cursor will be located.
• CURSOR parameter of DPAGE statement:CURSOR=(line,column,cfield)
MFLD CFIELD,LTH=4• 05 IM-CURSOR-LOCATION.
10 IM-CURSOR-LINE PIC S9(3) COMP.10 IM-CURSOR-COLUMN PIC S9(3) COMP.
IMS DC Slide: 70
• Paging: Is a facility that lets message be broken down into components for display, for processing or for both.
• Physical Paging / Logical Paging• Physical Paging: A message with a fixed number of segments is
further divided into parts that are sized properly for a particular device.
• Implement physical paging through the DFLD statement.Ex: POS=(8,12,3)
IMS DC Slide: 71
FIELD3 DFLD POS=(3,12) FIELD3 DFLD POS=(3,12)FIELD4 DFLD POS=(4,12) FIELD4 DFLD POS=(4,12)…………………………… ……………………..FIELD14 DFLD POS=(14,12) FIELD14 DFLD POS=(3,12,2)FIELD15 DFLD POS=(15,12) FIELD15 DFLD POS=(3,12,2)FIELD16 DFLD POS=(16,12) FIELD16 DFLD POS=(3,12,2)FIELD17 DFLD POS=(17,12) FIELD17 DFLD POS=(3,12,2)FIELD18 DFLD POS=(18,12) FIELD18 DFLD POS=(3,12,2)
• Operator Physical Paging: Program Function keys could be used.
• PFK=(PFKIN,08=NEXTPP,10=NEXTMSGP)
Multiple Physical Page Input
IMS DC Slide: 72
• MFS provides a facility to generate a single physical input message from multiple physical pages.DPAGE StmtMULT=YES
• Operations:• Operator presses ENTER key for each Screen• PF1 to skip over the screen without making an entry• Operator can use a PF key associated with MFS operator
command ENDMPPI to signal to MFS that multiple physical page input is over and complete input message can be constructed.
• CURSOR=((3,12),(3,12)),MULT=YESS
Logical Paging
IMS DC Slide: 73
• A logical page is usually associated with a single screen image.• With logical paging, we can send multiple occurrences of the
same screen, but with different data, as part of one output message.
• Logical paging is often used for applications that produce relatively large amounts of output.
• A group of related fields either on the screen or in a message is called a Logical page.
• Logical Page implemneted by LPAGE & DPAGE• DPAGE: Device Page, 1 - 8 char label to link to Lpage• LPAGE: Message Page
Operator Logical Paging Commands
IMS DC Slide: 74
• Command Action• = Move Forward one logical page• =nnn Move to logical page nnn• =l Move to last logical page• =-nnn Move backward nnn logical pages• =+nnn Move forward nnn logical pages
• For the operator to use the logical paging commands, a device field should be present into which he can enter paging commands.
How to define message pages
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• LPAGE, no other function other than logical pages• Codes only in format sets that don’t use logical paging• LPAGE - DPAGE relationship:
– SUMLPAGE LPAGE SOR=SUMDPAGE,….• How does MFS know which LPAGE to select?• Program has to move an identifying value to a particular field
in the output message segment.SUMLPAGE LPAGE SOR=SUMDPAGE,
COND=(LPAGEID=,’S’)SEG
LPAGEID MFLD LTH=1
How to support operator logical paging
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• Enable Operator logical pagingPAGE = YES (on the MOD)
• The above statement tells MFS to examine a related input message to see if they begin with an operator logical paging command.
PAGECMD DFLD POS(22,17),LTH=5,ATTR(NOPROT,ALPHA,NORM,NOMOD)
SEGMFLD PAGECMD,LTH=5,
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• Alternate Destination Concepts :– The application Program that’s processing a
Single Input Message can send multiple Output Message to Multiple Destinations.
– ISRT call is issued but only difference is that the call specifies Alternate PCB instead of I/O PCB.
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– Alternate PCB (ALTPCB), which are specified in the programs PSBGEN job, name the other terminals or transactions to which the program can send Messages.
ApplicationProgram
DataBase
Terminal
Printer
Input Message
Output Message(IOPCB)
Output Message
(ALTPCB)
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• Conversational Application– There are three ways to maintain Data
between Terminal Interaction.• Store Data in the Terminal Screen.• Store Data in the Databases• Store Data in the IMS provided Scratch Pad
Area.
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• Advantages & Disadvantages of these Techniques.– The First technique, is suitable only if the
Data is Simple & Non-Critical. – The Second Technique, makes your Program
more complicated and less efficient.– The Last Technique, is to use a special area
IMS provides just for that Purpose : The Scratch Pad Area (SPA).
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• Scratch Pad Area (SPA)– A conversational Program must use a SPA.– A Unique SPA is associated with each
terminal that’s running a conversational transaction.
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• Using SPA:– Define I/O Area for SPA :
01 SPA-IO-AREA.05 SPA-LL PIC S9(4) COMP.05 SPA-ZZ PIC S9(4) COMP.05 SPA-CI PIC S9(4) COMP.05 SPA-TRAN-CODE PIC X(8).05 SPA-USER-DATA PIC X(---).
– The area is much similar to the Message Segment– In Addition to LL & ZZ fields, the SPA contains a Third
binary halfword CI (Conversational Identifier) which IMSuses to keep track of SPA.
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• IMS Calls in Conversational Programs :– In Conversational Programs, SPA should be
retrieved first before retrieving Message Segments. This is done by issuing a ‘GU’ call against I/O PCB.
CALL ‘CBLTDLI’ USING DLI-GUIO-PCB-MASKSPA-IO-AREA.
IMS DC Slide: 84
– To save Data in the SPA, an ISRT call is issued against I/O PCB.
CALL ‘CBLTDLI’ USING DLI-ISRTIO-PCB-MASKSPA-IO-AREA
– You must not send an output Message Segment before you have saved the SPA.
– At the start of conversation, the SPA is set to Binary Zeros.
IMS DC Slide: 85
• Program Switching :– Switching from on Conversational Program to
Another requires that both the SPA & Message to be processed by the second program be transferred.
– There are two kinds of Program-to-Program Message switches
• Immediate Program Switching.• Deferred Program Switching.
• Immediate Program Switching :
Application Program - 1
Application Program - 2
Terminal
Output Message
Input Message
SPA
Switch Message Segment
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– The Program that receives the input Message is not the same one that responds to the Terminal.
– The First Program passes in SPA and other necessary data to the second Program, which does additional processing and respond to the originating terminal.
• Deferred Program Switching :
Application Program - 1
Application Program - 2
Terminal
Output Message 2
Input Message 1
SPAOutput Message 1
Input Message 2
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IMS DC Slide: 89
– A single Conversation involves two different Application Programs, one for each of two terminal Interactions.
– The data stored in SPA is passed from the first program to the Second.
– The second program isn’t invoked until the user sends the next input message
– This technique can impose less overhead on the IMS system & can result in faster response.
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• Logging:– Records all Database Updates, all Message
queued and all program scheduled.– These Information can be used to restore the
system if a failure occurs.
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– MTO (Master Terminal Operator) can manage other terminals in the network, as well as messages & programs execution in dependant Regions.
– The system maintains mtologs where the necessary details are stored when the abend occurs.
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• Recovery:– IMS provides extensive facilities for
Recoveries in the event of failure– If an Application Program Abends, IMS
automatically reverse or Rollback the changes it has made to the Databases and Message Queues.
IMS DC Slide: 93
• Checkpointing:– The checkpoints are taken automatically with each
transaction a program processes. (This is called Single Mode Processing.)
– In Multiple Mode Processing, the only automatic checkpoint is at the End of the Program. However, the program can force a checkpoint by issuing CHKP call, which causes IMS to write a Checkpoint Record to the Log.
– The Checkpoint Call Syntax:
CALL ‘CBLTDLI’ USING DLI-CHKPIO-PCB-MASKINPUT-MESG-IO-AREA.
Thank You
IMS DC Slide: 94
