IMS DC is a hierarchical database management system supplied by IBM that runs on mainframe computers. It has two main components: Data Base (DB) processing and Data Communication (DC) processing. DC handles information in the form of messages that flow between remote terminals and application programs. Major kinds of online programs that can be written for IMS DC include inquiry programs, data entry programs, maintenance programs, and menu programs.

1. IMS DC
IMS DC Slide: 1
Pre-Requisite: IMS DB knowledge

2. 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.

3. Interactive Programs
IMS DC Slide: 3
• Major Kinds of Online Programs that can be written:
– Inquiry Programs
– Data Entry Programs
– Maintenance Programs
– Menu Programs

4. 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

5. Software Components of an IMS DC system
Data base & datasets
Communication
Control
Editing Modules
(MFS)
Queue Manager
QPOOL
Message Queue Overflow
datasets
VTAM Terminals
MVS address
Space
VTAM
Non VTAM
Terminals
MVS Address space
IMS / VS control
region
Logging
DLI
MVS address
Space
MPP region
MVS address
Space
MPP region
MVS address
Space
MPP region
MVS address
Space
BMP region
Logging data sets
VTAM Terminals
IMS DC Slide: 5

6. IMS-DC OFFERS:
IMS DC Slide: 6
1. A way to improve customer and internal service by providing
current 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

7. 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

8. ELEMENTS OF AN IMS-DC ONLINE SYSTEM
TERMINALS
MESSAGES
REGIONS
PROGRAMS
DATABASES
IMS CONTROL BLOCKS
IMS LOGS
IMS DC Slide: 8

9. IMS STANDS BETWEEN THE TERMINAL AND THE APPLICATION PROGRAM
TERMINAL
DATABASE
IMS
INPUT
MESSAGE
OUTPUT
MESSAGE
INPUT
MESSAGE
OUTPUT
MESSAGE
PROCESS
IMS DC
PROGRAM
IMS DC Slide: 9

10. 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 operator
MPP: Message Processing Program, scheduled by IMS

11. 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.

12. How IMS uses MVS regions
IMS DC Slide: 12
Regions in IMS.
IMS/VS CONTROL
REGION
TERMINAL TERMINAL
LOG DATASETS
MPP
REGION
MPP
REGION
MPP
REGION
BMP
REGION
DATABASE DATASETS

13. 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.

14. 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.

15. 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.

16. 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

17. Terminals & Security under IMS
IMS DC Slide: 17
• SMU Security Maintenance Utility
RACF Resource Allocation & Control Facility
• Transaction Security
• SIGN ON verification
• LTERM security

18. How IMS Manages Input messages
IMS DC Slide: 18
• Three kinds of IMS input messages:
a. Transactions
b. Terminal to Terminal message
c. 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

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. DL/I calls for DC Operation
IMS DC Slide: 24
• CALL ‘CBLTDLI’ USING DLI-GU
IO-PCB-MASK
INPUT-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.

25. 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.

26. 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-3
05 IO-PCB-TIME PIC S9(6)V9 COMP-3
05 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).

27. 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.

28. 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.

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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-DATA
PERFORM 150-INSERT-OUTPUT-SEGMENT.
110-GET-INPUT-MESSAGE.
CALL 'CBLTDLI' USING DLI-GU
IO-PCB-MASK
INPUT-MESSAGE-IO-AREA.
IF IO-PCB-STATUS-CODE = 'QC'
MOVE 'Y' TO END-OF-MESSAGES-SW.
IMS DC Slide: 35

36. 120-GET-INVOICE-DATA.
MOVE IN-INVNO TO INVOICE-NO-SSA-VALUE.
CALL 'CBLTDLI' USING DLI-GU
CR-PCB-MASK
RECEIVABLE-SEGMENT
INVOICE-NO-SSA.
IF CR-PCB-STATUS-CODE NOT = SPACE
MOVE '9999' TO OP-STAX
ELSE
MOVE R-INVOICE-NUMBER TO OP-INVNO
MOVE R-STAX TO OP-STAX.
150-INSERT-OUTPUT-SEGMENT.
CALL 'CBLTDLI' USING DLI-ISRT
IO-PCB-MASK
OUTPUT-MESSAGE-IO-AREA
MFS-MOD-NAME.
IMS DC Slide: 36

37. 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

38. MFS Control Blocks
IMS DC Slide: 38
Terminal
Device Input
Format (DIF)
Device Output
Format (DOF)
Mesg Input
Descriptor
(MID)
Mesg Output
Descriptor
(MOD)
Application
Program
Input Message
Sent by Terminal
Output Message
Sent by Program
Output Message
Recv by Terminal
Input Message
Recv by Program
• To process a Transaction, MFS uses 4 Control Blocks.

39. 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.

40. 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.

41. 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>

42. 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 Statements
Message descriptor control statements
Compilation Control Statements

43. 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
DEV
DIV
DPAGE
DFLD
DFLD
DPAGE
FMTEND

44. 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.

45. Format Set
IMS DC Slide: 45
INQDF FMT
DEV TYPE=(3270,2),FEAT=IGNORE,DSCA=X’OOAO’
DIV TYPE=INOUT
DPAGE CURSOR=((1,2))
TRANINV DFLD POS=(1,2),LTH=15
OUTTEXT DFLD POS=(3,2),LTH=702
FMTEND
INQO MSG TYPE=OUTPUT,SOR=(INQDF,IGNORE),NXT=INQI
SEG
MFLD OUTTEXT,LTH=702
MSGEND
INQI MSG TYPE=INPUT,SOR=(INQDF,IGNORE),NXT=INQO
SEG
MFLD TRANINV,LTH=15
MSGEND
END

46. DEV Control Statement
IMS DC Slide: 46
• PFKDF FMT
DEV TYPE=(3270,1)
FEAT = IGNORE
PFK=(PFKTEXT,1=‘01’,2=‘02’,8=‘08’)
FMTEND
PFKEXI MSG TYPE=INPUT,
SOR=(PFKDF,IGNORE),
NXT=PFKDFO
SEG
MFLD PFKTEXT,
LTH=2
MSGEND

47. 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

48. 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’)

49. DEV TYPE= (3270,1)
(3270,2)
3270-An
,FEAT=IGNORE
[,PFK=(pfkeyfield,[integer=] ‘literal’
NEXTPP
NEXTMSGP [,…])]
ENDMPP1
IMS DC Slide: 49

50. 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.

51. DFLD
IMS DC Slide: 51
• Specifies where on the screen a field is located & how large the
field 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=8
ATTR=(HI,PROT)

52. 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

53. 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

54. 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.

55. Message Descriptor Control Statements
IMS DC Slide: 55
• MSG
LPAGE
PASSWORD
MFLD
SEG
MFLD
MFLD
LPAGE
SEG
MFLD
MSGEND

56. MSG
IMS DC Slide: 56
• msgname MSG TYPE=(INPUT / OUTPUT )
SOR =(dfname,IGNORE)
NXT=nextmsgname
PAGE=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.

57. MFLD Control Statement
IMS DC Slide: 57
• MFLD {SOURCE / DESTINATION }
LTH = Length
JUST={L / R}
FILL=fillchar
ATTR=(YES)
• Input Message Field Descriptor:-
MFLD ‘DI2 ‘, LTH=8
MFLD INVNO,LTH=6
MFLD (INVNO,’000000’),LTH=6
• Output Message field:-
MFLD (CURDATE,DATE2)

58. 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.

59. 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

60. 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.

61. IMS DC Slide: 61
• Format of the ISRT call with the MOD name segment
CALL ‘CBLTDLI’ USING DLI-ISRT
IO-PCB-MASK
OUTPUT-MESSAGE-IO-AREA
MFS-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 to
cause an input message that begins with:
/format mod-name

62. Screen Example
IMS DC Slide: 62
• Receivables Menu Date: xxxxxxx
PF1 Enter Cash Receipts
PF2 Display Invoice Summary

63. Format Set for Menu Program
IMS DC Slide: 63
• MENUDF FMT
DEV TYPE=(3270,2),FEAT=IGNORE,SYSMSG=ERRMSG,
PFK=(PFKFIELD,’/FOR CRO ‘,’/FOR DI2O ‘,’/FOR DIDSO’)
DIV TYPE=INPUT
DFLD ‘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=MENUO
SEG
MFLD PFKFIELD,LTH=10
MSGEND
MENUO MSG TYPE=OUT,SOR=(MENUDF,IGNORE),NXT=MENUI
SEG
MFLD (CURDATE,DATE2)
MFLD LTH=1
MSGEND

64. 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.

65. 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. (Low
Values)

66. 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

67. Cursor & Attribute Control
First byte (Cursor Control) Second Byte (Attribute Control)
0 0 0 0 0 0 1 0
Bit 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
Cursor
Positioning
Shift Intensity Pen MDT
Protection
Attribute Override
Byt
e
Bits Function Values
1 0-1 Cursor Pos. 00 Cursor Positioning not requested
11 Position cursor at this field. (Values 01 and 10 are invalid)
2-7 000000 (Always)
2 0 1 (Always)
1 Attribute
Override Type
0 Use the attr. Specifications that follow to activate only specified
attributes (that is attributes whose corresponding override bit is on
1 Use the attribute specs that follow to replace all device field attribu
2 Protect. Attr. 0 Unprotected
1 Protected
3 Shift Attribute 0 Alphanumeric Shift
1 Numeric Shift
4-5 Intensity Attrib 00 Normal Intensity
01 No-display
10 Bright Intensity
11 Bright Intensity
6 Light-pen Attr 0 Should be 0 for non- Light – Pen applications
7 MDT 0 MDT off
1 MDT on
IMS DC Slide: 67

68. 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 Cursor
To 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.

69. 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.

70. 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)

71. 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)

72. Multiple Physical Page Input
IMS DC Slide: 72
• MFS provides a facility to generate a single physical input
message from multiple physical pages.
DPAGE Stmt
MULT=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

73. 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

74. 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.

75. How to define message pages
IMS DC Slide: 75
• 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

76. How to support operator logical paging
IMS DC Slide: 76
• Enable Operator logical paging
PAGE = 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)
SEG
MFLD PAGECMD,LTH=5,

77. IMS DC Slide: 77
• 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.

78. IMS DC Slide: 78
– Alternate PCB (ALTPCB), which are
specified in the programs PSBGEN job,
name the other terminals or transactions to
which the program can send Messages.
Application
Program
Data
Base
Terminal
Printer
Input Message
Output Message
(IOPCB)
Output Message
(ALTPCB)

79. IMS DC Slide: 79
• 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.

80. IMS DC Slide: 80
• 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).

81. IMS DC Slide: 81
• 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.

82. IMS DC Slide: 82
• 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 IMS
uses to keep track of SPA.

83. IMS DC Slide: 83
• 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-GU
IO-PCB-MASK
SPA-IO-AREA.

84. IMS DC Slide: 84
– To save Data in the SPA, an ISRT call is issued
against I/O PCB.
CALL ‘CBLTDLI’ USING DLI-ISRT
IO-PCB-MASK
SPA-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.

85. 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.

86. • Immediate Program Switching :
Application
Program - 1
Application
Program - 2
Terminal
Output Message
Input Message
SPA
Switch
Message
Segment
IMS DC Slide: 86

87. IMS DC Slide: 87
– 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.

88. • Deferred Program Switching :
Application
Program - 1
Application
Program - 2
Terminal
Output Message 2
Input Message 1
SPA
Output Message 1
Input Message 2
IMS DC Slide: 88

89. 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.

90. IMS DC Slide: 90
• 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.

91. IMS DC Slide: 91
– 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.

92. IMS DC Slide: 92
• 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.

93. 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-CHKP
IO-PCB-MASK
INPUT-MESG-IO-AREA.

94. Thank You
IMS DC Slide: 94