IMS DC

IMS DC

Information Management SystemDC concepts and programming

• General Online concepts

• Batch vs online differences

• IMS DC Block diagram

• Messages and Queues

• COBOL basics for MPP Programs

• Message Format Service (MFS)

IMS DC CONCEPTS

General Online Concepts

• Interactions are driven by transactions• User enters input through a screen, programs edit/validate

the input data and processes the information for display back to the user

• More emphasis on response time, security, data integrity and system performance

• Applications where quick response to a given request is required are good candidates for online

Batch Online

• Driven by input records Driven by user

• Submitted through JCL's Transaction oriented

• Processing time is longer Processing time minimum

• Only one user can process Multiple users

• Batch programs will have exclusiveShared control control over data

Batch vs Online Differences

IMS DC Block Diagram

Terminal

MessageQueues

Log Datasets

MVS AddressSpace MPP

MVS AddressSpace MPP

MVS AddressSpace BMP

CommunicationControl

MFS Module

Queue manager

DL/I

MVS Address Space

Logging

QPOOL

DB Datasets

IMS VS Control Region

The Resources that IMS-DC controls

•There are two main categories of system resources that are defined to IM S system definition:

A.Application Resources.

B.Data communication Resources.

Application Resources:

A.Application Programs.

B. Transaction Codes.

C. Message Queues.

D.Data Bases.


There are two types of application programs in the IMS DB/DC environment.

1.MPP(Message processing programs)

2.BMP(Batch processing programs)

Out of these two application programs ,our focus is mainly on MPP which plays major role in IMS/DC environment.The scheduling of MP programs is entirely under the control of IMS.A message processing program is automatically loaded by IMS when a message to be processed by that program is received.


Scheduling Techniques:

A concept of PRIORITY SCHEME is used in determining scheduling of IMS/DC programs in MPP region.

Each transaction has two priorities associated with it: NORMAL PRIORITY and LIMIT PRIORITY.In addition,each transaction has a LIMIT COUNT.These three numbers are specified in the TRANSACT macro for each transaction type.

IMS select the transaction having the highest priority.To determine whether to use the normal priority or the limit priority,IMS looks at how many transactions with each transaction code are stored in each message queue.If the number of transactions in a particular


Scheduling Techniques:

Queue is greater than or equal to that transaction code’s LIMIT COUNT,the High PRIORITY is used.If the number of messages queued is less than the LIMIT COUNT,the NORMAL PRIORITY is used.

MP programs are identified to IMS during IMS system definition in APPLCTN system definition macros.

EX: APPLCTN PSB=LCU040A,PGMTYPE=ONLINE

Messages,Queues

• Message queueing: Message is a Unit of data that is transmitted between a program and a terminal.

• When IMS receives a message from a terminal it’s not passed immediately to the destination, instead they go for MFS edit.

• The entry a terminal user makes to invoke a transaction and the execution of the application program with which it is associated are not synchronous.

• The IMS stores the transaction temporarily, which is message queuing and the IMS modules that performs this are collectively called the queue manager (QPOOL).

• Queues often contain more transactions that can be processed at one time, a priority scheme is used in determining which transaction to select first from the queues.

Messages,Queues

• There are three types of input messages:

• Transactions(A message that has an MP program as a destination,whether it originates at a terminal or in a program ,is called a TRANSACTION).

• Terminal-to-terminal message switches

• IMS commands

• You can Identify input message type

• If IMS uses the value in 8 bytes characters name in an application program i.e transaction code.

These transaction codes are defined to IMS during IMS system definition with TRANSACT macros.

Messages,Queues

EX: TRANSACT CODE =TRANS A TRANSACT macro names a transaction code,and follows the APPLCTN macro for the program that processes it.This indicates to IMS which MP program processes each type of transaction.•If the first 8 characters contain an LTERM name i.e message switch•If the input message begins with a slash IMS interprets it as a command.

IMS Data Bases

Programs that run in the IMS/DC environment cannot indiscriminately access any IMS data base.System definition macros do not indicate which data bases are processed by which programs.

Data Communication Resources

• A second category of resource that must be defined during IMS system definition includes all the data communications hardware in the communications network.Data communication hardware used ny IMS/DC is managed by TELEPROCESSING ACCESS METHODS-TP ACCESS METHODS.

The important physical resources under the control of IMS/DC are communications lines that handle data communications,often telephone lines,and remote terminals.

Data Communication Resources

• LTERM NAME is the the terminal from where the message has been generated and sent into IMS

• The terminal is connected to IMS , hence IMS recognizes the terminal name itself no need for explicit mentioning of the Name

• MOD – Message output descriptor is a part of MFS which represents the medium to key in the messages from the terminals into the IMS

COBOL Basics for MPP Programs

• The elements you code in a DC program to process messages are extensions of the same elements you use to process data bases.

• DL/I calls for DC operations.

• PCB mask for DC operations.

• How to retrieve the input message segments.

• How to send output message segments.

• Comparison of Data base call with Data communication call.

About DL/I

DL/I actually known as Data language/1

DL/I is a interface between database and IMS/DC

It is IBM’s name for the collection of software modules

DL/I intercepts all requests that programs make for accessing the data base

IMS uses DL/I functions to communicate with DL/I modules

COBOL Basics for MPP Programs contd...

• DL/I calls for DC operations

The basic unit of I/O for a data communication DL/I call is a segment.However unlike database segments,message segments are not stored in hierarchically.Instead they represent the parts of a message.

• PCB mask for DC operations A DC call must specify a linkage section PCB mask similar

to the way it is done in a DB call.


• This is not a database PCB mask, it’s for the message processing, in IMS terminology it’s called the I/O PCB

• It must be the first PCB listed on the ENTRY statement

• All you have to do is specify the name of the I/O PCB on the ISRT call that sends an output message.


• Sample PCB layout.• 01 IO-PCB-MASK.

05 IO-PCB-LOGICAL-TERMINAL PIC X(8).

05 FILLER PIC XX .

05 IO-PCB-STATUS-CODE PIC XX.

05 IO-PCB-DATE PIC S9(7) COMP-3.

05 IO-PCB-TIME PIC S9(6) V 9 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).


• Input-output area (I/O AREA):

• How to define i/o area for an input message segment

• 01 INPUT-MESSAGE-IO-AREA.

05 IM-LL PIC S9(3) COMP. (length of entire input message)

05 IM-ZZ PIC S9(3) COMP. (Reserved for IMS for input)

05 IM-TRANS-CODE PIC X(9).(1-8 byte value followed by space)

05 IM-INVOICE-NO PIC X(6). (Enough area to hold i/p message)


• How to define i/o area for output message segment;

• 01 OUTPUT-MESSAGE-IO-AREA

05 OM-LL PIC S9(3) COMP VALUE +706. (Can modify in o/p

only)

05 OM-ZZ PIC S9(3) COMP VALUE ZERO. (Reserved by IMS)

05 OM-TEXT PIC X(702).

• Before you issue an ISRT call you need to be sure that the LL field in the i/o area contains the actual length of the message that’s to be sent including initial 4 bytes.


• How to retrieve an input message segments.

To retrieve an input message, an application program issues either

a single GU call or a GU call followed be one or more GN calls. The technique used in the application program depends on how many segments the input message contains.


• How to send an output message.

You send output message segments by issuing ISRT calls that specify the I/O PCB.

• The message will be directed to the terminal mentioned in the I/O PCB

ie the original terminal

• There is a provision of redirecting the messages to other terminals which are not the original one this can be done using ALT-IO-PCB


•ALT-IO-PCB needs to be mentioned in the linkage section along with the IO-PCB to utilize it

•The LTERM NAME needs to be changed in ALT-IO-PCB before giving an insert call unlike the normal DC call to mention the new destination

The structure of the ALT-IO-PCB is much simple when compared to IO/PCB

01 ALT-PCB-MASK

05 ALT-PCB-DESTINATION PIC X(8).

05 FILLER PIC XX.

05 ALT-PCB-STATUS-CODE PIC XX.


• Comparison of Data base call with Data communication call. A data base call CALL ‘CBLTDLI’ using DLI-GU CR-PCB-MASK RECEIVABLE-SEGMENT INVOICE-NO-SSA . A data communication call

CALL ‘CBLTDLI’ using DLI-GU IO-PCB-MASK INPUT-MESSAGE-SEGMENT.


• A call to get the input messages from the message Queue will be as follows

CALL CBLTDLI(GU,

IO – PCB – MASK

INPUT-MESSAGE-IO-AREA)

• The parameters are already explained in the previous slides

• The IO-PCB-MASK should be declared in the linkage section which will follow by an Entry stmt in procedure division

• INPUT-MESSAGE-IO-AREA is declared in the working storage or declared as a copy book

Message Format Service

• It is a part of IMS TM that uses control blocks that you define to format messages between a terminal and an MPP.

• The MFS control blocks indicate to IMS TM how you want your input and output messages arranged.

• MFS makes it possible for an MPP to communicate with different types of terminals without having to change the way it reads and builds messages.

• Formats Display Screens and Messages for Data Communication Programs

• Makes Application program independent of Terminal Types

• Uses 4 Control Blocks to format Screens and Messages

• Related group of 4 Control Blocks are called FORMAT SET

Message Format Service contd...

DEVICE INPUT FORMAT (DIF) MESSAGE INPUT DESCRIPTOR (MID) MESSAGE OUTPUT DESCRIPTOR (MOD)

DEVICE OUTPUT FORMAT (DOF)

CONTROL BLOCKS



DIF

DOF

MID

MOD

Terminal App. Program

MFS


• DEVICE INPUT FORMAT(DIF) Interprets Data as its received from Terminal

• MESSAGE INPUT DESCRIPTOR 1(MID) How data should be formatted for presenting to the Application

program

• MESSAGE OUTPUT DESCRIPTOR (MOD)• Interprets Data received from Application Program

• DEVICE OUTPUT FORMAT(DOF)• How data should be formatted for Transmission to the Terminal


• FORMATSET

Defines the way the screens to be used in an application

Defines the format of the Input and Output messages an Application program can receive and send

Specifies the relationships between the data on the screen and data on the message


• Format of a Control Statement in FORMAT SET

1 8

LABEL OPERATION

10 14 16 71 72

OPERAND

80


FMT:

• Specifies the Beginning of Format Set Control

Statements

Syn: LABEL FMT

• Label should not be more than 6 Characters

FMTEND:

• Specifies the End of Format Set Control Statements

Syn : LABEL FMTEND


“DEV” CONTROL STATEMENT

• Identifies beginning of Control Statements for a particular Device Type

Syn: DEV TYPE=(DEVICE_TYPE),

FEAT=(IGNORE),

PFK=(PFK_FIELD),

DSCA=X’nnnn’,

SYSMSG=MSG_FIELDS


DEV - TYPE:

• Specifies the Device Models for which Device Format Blocks should be created

VALID VALUES FOR 3270 TERMINAL:

3270,1 - 12 LINE

3270,2 - 24 LINE

(3270,A1{,A2,A3,A4,A5,A7})


DEV - FEAT:

• Specifies that DIF or DOF generated for this DEV Statement will work with the Indicated 3270 terminal Type, regardless of any Special features installed on it

Syn: FEAT=IGNORE


DEV - PFK:

• Allows to Specify how MFS should treat Program Function Keys

Syn: PFK=(MSG_FLD,1=‘01’,2=‘02’)

MSG_FLD is the field of Message and gets populated with corresponding Value of the PF Key pressed


DEV - DSCA:

• Specifies the default Terminal Action that’s performed when an Output message is sent to a 3270 device type

Syn: DSCA=X’00A0’

DEV - SYSMSG:

• Allows to specify Device field in which messages that come to the Terminal from IMS will be displayed

Syn: SYSMSG=ERR_FIELD

MetLife:

X’00A0’ erases all The unprotected fields on the screen with this value literal’s are sent to the screen only during Initialization

MetLife:

X’00A0’ erases all The unprotected fields on the screen with this value literal’s are sent to the screen only during Initialization


“DIV” CONTROL STATEMENT

• Specifies the device format Specification Control Statements

• There should be one DIV for each of the Format control Block (DIF or DOF)

• For 3270 terminal type there will be only one DIV statement


DIV - TYPE

• Syn :TYPE = INOUT

• INOUT Specifies same device format be used for both DIF and DOF

“DPAGE” CONTROL STATEMENT

• Specifies a Device format used to handle Multiple Logical Pages

• Two parameters in DPAGE are used to Specify Initial Cursor positioning and Fill character


DPAGE - CURSOR

• Specifies default Cursor Position

Syn: CURSOR=((Line_No,Column_No,C_field))


DPAGE - FILL

• Specifies FILL character to be used for Output Device Fields

Syn: FILL= FILL_CHAR

Valid FILL-CHAR for 3270.

PT - Program Tab - The output device fields that are not filled are

followed by a this character till the remainder of device field

this avoids MFS transmitting blanks to partially fill fields and

also erases previously displayed data.

C’c’-Character to be used

X’hh’-Hex Values


“DFLD” CONTROL STATEMENT

• DFLD Statements identifies individual fields on the screen

• Syn: LABEL DFLD POS=(LINE_NO,COL_NO), LTH=LENGTH,

ATTR=(ATT1,ATT2…) • LABEL is required only for those fields which needs a mapping Message

field

• For Constant Literal on the Screen No Label is required


“ATTR ” CONTROL STATEMENT

• To position the cursor from an application program you can use 2 techniques

1. Field oriented cursor control (ATTR=YES)on MFLD statements.

2. Absolute cursor control.


LAYOUT OF DEVICE FORMAT SET

FMT

DEV

DIV

DPAGE

DFLD

.

DFLD

DPAGE

FMTEND


MESSAGE CONTROL STATEMENT

• Starts with MSG statement

Syn: LABEL MSG TYPE = INPUT/OUTPUT

SOR=(DF_NAME,IGNORE)

[,NXT=NEXT_SEG_NME]

[,PAGE=YES]



TYPE - INPUT:

• Specifies Control Statements to be following are used to generate MID( Message Input Descriptor)

TYPE - OUTPUT:

• Specifies Control Statements to be following are used to generate MOD( Message Output Descriptor)



SOR:

Syn: SOR = (DF_NAME,IGNORE)

DF_NAME: Label Coded in the FMT statement

IGNORE: Indicates Device format coded with FEAT=IGNORE should be used with MID/MOD



NXT:

Syn: NXT = NEXT_MSG_NAME

NEXT_MSG_NAME

IF TYPE IS ‘INPUT’

NEXT “MOD” NAME

IF TYPE IS OUTPUT

NEXT “MID” NAME



LPAGE:

• Identifies the beginning of a series of control statements for a logical page subordinate to a MSG statement

PASSWORD:

• Identifies the beginning of a series of MFLD statements that are used to construct the password for an input message.You may code only one PASSWORD statement subordinate to an LPAGE statement



• SEG: Identifies the beginning of a series of MFLD statements the make up a

message segment.You may code multiple SEG statements subordinate

• MFLD:

• Defines fields in the message segment

• There should be one-to-one mapping between MFLD in the Message Descriptor and fields in I/O area layout in Application Program



MFLD:

Syn: MFLD = SOURCE/DESTINATION

[,LTH= LENGTH]

[,JUST=L/R]

[,FILL = FILL_CHAR]

[,ATTR=YES]



MFLD - SOURCE:

• Specifies the Source of the Data MFS will map into this field

• It can be either

LITERAL or DEVICE_FIELD

Literal is used when a fixed value should be part of every message



MFLD - SOURCE:

Syn: MFLD=(LITERAL/DFLD/(DFLD,LITERAL))

DFLD - Label of the DFLD from which data for this MFLD

will be mapped

(DFLD,LITERAL) - If the device field contains data ,the value specified for literal will be used instead



MFLD - DESTINATION:

Syn: MFLD=(LITERAL/DFLD/(DFLD,SYSLIT))

DFLD - Label of the DFLD into which data from this MFLD will

be mapped

(DFLD,SYSLIT) - If the device field contains data,the SYSLIT(System Literal) values be supplied instead



MFLD - DESTINATION:

SYSLIT : DATE1 SYSTEM DATE IN YY.DDD

DATE2 SYSTEM DATE IN MM/DD/YY

DATE3 SYSTEM DATE IN DD/MM/YY

DATE4 SYSTEM DATE IN YY/MM/DD

TIME SYSTEM TIME IN HH:MM:SS

LTNAME LOGICAL TERM. NAME



MFLD - DESTINATION:

• When SYSLIT is Specified Do Not Specify

LTH Parameter on MFLD Statement

Field in Application Program’s O/P message segment



MFLD - LTH:

• Specifies the Length of the MFLD Statement

• Can be omitted for a Literal

• Should not be Specified for a SYSLIT



MFLD - JUST:

• Specifies the Justification for the MFLD

• Valid Values are

L - LEFT

R - RIGHT



MFLD - FILL:

• Specifies PAD characters be used for a MFS field

• For Numeric Field

FILL = C’0’

• To Specify No Pad Characters

FILL = NULL



MFLD - ATTR:

• YES allows Dynamic Attribute Modification

• For all the MFLD fields with ATTR=YES, length should be 2 bytes more than the normal MFLD to allow dynamic attribute specifications.

Message Format Service


MSGEND:• Specifies END of Message Control Statement

MSG LPAGE PASSWORD MFLD SEG ……. MFLD MFLDMSGEND

Important IMS libraries & Functionalities

IMV2.RESLIB

•This system data set contains all the load modules that makeup the IMS Software, including both DL/I and data communication component.The operating system must have access to this data set or equivalent, via a SETPLIB or JOBLIB DD statement whenever there is a program is executed.

•DFSRC000 , ZFSRC000 , FABHX034 --- Batch initialization Module existing in the RESLIB.

IMV2.PGMLIB

All IMS application program load modules are stored in this data set.

Important IMS libraries & Functionalities contd..

IMV2.PSBLIB & IMV2.DBDLIB

•Contains the libraries related to PSB and DBD.

IMV2.MACLIB

•Used generally by data base administrator. It contains the definitions of the macros that are used to generate the IMS system and of other macros, such as DBDGEN and PSBGEN macors.

IMV2.PROCLIB

The IMS cataloged procedures supplied to IMS are stored here. The IMS procedures are stored in the standard system library, and IMV2.PROCLIB is not used in daily production.

Important IMS libraries & Functionalities contd..

IMV2.ACBLIB

When an IMS program is executed, IMS must combine the information DBD and PSB before the application program is executed. To avoid causing IMS to do this each time a program run the DBA may choose to merge the DBD and PSB information in advance. To do this a procedure called ACBGEN(Application Control Block Generation) is executed. The IMV2.ACBLIB data set is used to store the combined DBD and PSB.

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