This section of the Natural CICS Interface documentation describes the various ways of how Natural can be invoked from user programs.
It covers the following topics:
This section covers the following topics
A Natural session can be activated by user front-end programs with one of the following commands:
or the equivalent CICS macro level requests.
EXEC CICS XCTL/LINK, the
parameters used by Natural can be passed in a CICS COMMAREA or in the TWA.
Natural determines the location of the startup parameters by inspecting the length of the COMMAREA passed to it during session initialization.
If the length is 22, Natural tries to locate the parameters in the COMMAREA, otherwise it is assumed that they have been passed in the TWA.
To identify a front-end program properly, it is mandatory that the first 4 bytes of the front-end parameter list represent the current transaction ID.
The transaction ID associated with the front-end program must have a TWA size that is equal to or greater than the Natural TWA size; see also ncitransact in Installing Natural CICS Interface on z/OS or Installing Natural CICS Interface on z/VSE in the Natural Installation documentation.
EXEC CICS RETURN IMMEDIATE,
the front-end parameters used by Natural can be passed in a CICS COMMAREA and
the dynamic parameters used by Natural can be passed with
INPUTMSGLEN (...) of the
RETURN IMMEDIATE command.
EXEC CICS START, the
front-end and dynamic parameters used by Natural can be passed with
LENGTH (...) of the
START command. The parameters are described on the following
EXEC CICS LINK with the
SYSID parameter pointing to a remote region, the
front-end and dynamic parameters used by Natural have to be passed in a CICS
COMMAREA. In addition also a
TRANSID parameter has to be
specified naming the transaction code of a mirror transaction with a TWA size
satisfying Natural's requirements.
It should be noted that the same restrictions as for asynchronous Natural sessions apply to Natural sessions invoked via DPL, that is, no input is possible (therefor the same dynamic parameter settings are recommended) and the caller just gets control back after Natural session termination.
A series of sample programs for the various programming techniques is supplied in the Natural CICS source library; see also Natural CICS Sample Programs
It is possible to start a Natural session from a Natural program
by calling the external subroutine
CMTASK. Refer to the sample
ASYNCICS in library
The following list of parameters must be supplied to invoke Natural from a user front-end program:
Invoking transaction ID
This value must be equal to the current transaction ID. Via the invoking transaction ID, Natural identifies that it was called by a user front-end program.
When being called with
Address/offset of dynamic parameter string
If dynamic parameter overwrites are to be evaluated, this value should be set to the address located 12 bytes before the dynamic parameter assignment string.
When being called with
Length of the dynamic parameter string
Zero indicates that no parameters are to be passed.
Natural transaction ID
The value specified is the transaction ID to be used for
controlling a pseudo-conversational Natural session, when being called with
If the Natural transaction ID is not specified, Natural restarts the transaction ID which initiated the current CICS task, and the front-end program regains control after each pseudo-conversational I/O.
Back-end program name
This 8-byte value is the program name to which control is
transferred at the end of the Natural session with a CICS XCTL command, rather
than restarting the calling transaction ID via
If this field is numeric in the first byte, Natural simply
For the conventions of calling non-Natural back-end programs, refer to the Natural Operations documentation.
On return to the front-end, Natural indicates in the TWA if the
session has terminated or not: when the session has terminated, the TWA holds
regular back-end information (see
Back-end Program Calling
Conventions in the Operations documentation),
else Natural puts the
NEXTTRANSID into the first
four bytes of the TWA.
If Natural is running in pseudo-conversational mode (profile
PSEUDO set to
ON) and has been invoked by
LINK (or the equivalent CICS macro level request), the original
invoking transaction is invoked each time Natural writes to a terminal and
waits for input, which means that Natural issues a "logical"
CICS RETURN TRANSID (..) after having written its restart
information into CICS temporary storage.
The invoking transaction must recognize this situation (for example,
by checking whether a
NEXTTRANSID has been sent or
by the existence of
NCOMxxxx TS records
NCOM is the Natural CICS parameter generation option and
xxxx is the terminal ID -) and pass
control back to Natural.
The advantage of this method is that, during the session, the front-end program can decide to pass control to another application (for example, COBOL) and to resume the Natural session later.
For further details see the
description in the Parameter Reference documentation.
Per design, Natural treats a LINK front-end program as a back-end program at session termination, that is, the Back-End Program Calling Conventions apply.
Make sure that the
NCOMxxxx TS records can be accessed by
all participating CICS AORs (for example via appropriate CICS TST
Alternatively the LINK front-end program can also pick up the NCI session restart information in CICS temporary storage on task termination and pass it in a CICS COMMAREA by itself; such a COMMAREA has then to be put into CICS temporary storage again prior to invoking Natural for session resume.
This front-end technique only works for terminal-bound Natural
sessions. Natural scans for start-up parameters supplied with the COMMAREA.
Note that when using this technique, potential dynamic parameters cannot be
passed chained to the front-end parameters, that is, the dynamic parameters'
address fields must be zero. Instead, potential dynamic parameters can be
passed via terminal input data, which are obtained by Natural by an
EXEC CICS RECEIVE command.
If the Natural session is a started task (that is, invoked by an
EXEC CICS START or
LINK/XCTL command by a front-end user program which has been
STARTed), Natural first scans for startup parameters
supplied with the COMMAREA, then it scans for parameters in the TWA and finally
it tries to obtain the necessary parameters by an
If the Natural session is initiated from a front-end program with
XCTL and no return program is specified (that is,
neither a fifth parameter in the session startup parameters nor a
PROGRAM specification in the Natural dynamic parameters
NTPRM macro), Natural restarts the user front-end
transaction at session termination via
TRANSID by internally simulating a
PROGRAM='RET=xxx' specification, with
xxx being the front-end transaction
To avoid a loop condition, logic must be included into the user front-end routine to decide whether a new session is to be started or an old session is to be resumed.
If the Natural session is invoked via DPL, Natural first determines
if it is directly invoked in the server region or indirectly via
EXEC CICS LINK/XCTL by a local front-end program.
When being invoked directly, Natural retrieves the start parameters from the
CICS COMMAREA. When being invoked indirectly, Natural scans for startup
parameters supplied with the COMMAREA, then it scans for parameters in the TWA.
On return Natural passes regular back-end data in the TWA when there is a local
LINK front-end program available, otherwise it returns the termination message
and potential back-end data in the remote client's COMMAREA.
If the Natural session is initiated from a front-end program and this program is also specified to be the return program, the user front-end should also check for the initiating transaction ID.
In particular this applies if the front-end program is not in pseudo-conversational mode but Natural is in conversational mode.
In this case Natural is invoked again rather than getting terminated, but this time without detecting that it is called by a front-end program, as the first parameter in the startup parameters is the Natural transaction ID.