IBM OS/390 User Manual
document is organized by source language type and goes into great detail at
that level and includes the I/O considerations.
that level and includes the I/O considerations.
The conversion of the CICS applications consists of two steps. First, the VSE
version of the CICS application subsystem is replaced with an OS/390 version.
The two different versions of CICS contain the interfaces to the respective control
programs. The second step deals with the application source code itself.
version of the CICS application subsystem is replaced with an OS/390 version.
The two different versions of CICS contain the interfaces to the respective control
programs. The second step deals with the application source code itself.
In general, the interfaces provided to the applications by the two versions of
CICS are the same, the source programs do not change and need only to be
recompiled with a corresponding OS/390 compiler. However, consideration
should also be given to the fact that certain application level interfaces available
in VSE may not be available in OS/390. The macro level API is one example.
Applications written with this interface will have to be changed to use the
command level API. Any access to system level control blocks should also be
reviewed. Additional considerations will be required if the CICS application
programs are interfacing with more than the CICS subsystem. Also, there are
some source language restrictions. This document contains a section describing
the CICS, DB2 and DL/I subsystems in great detail.
CICS are the same, the source programs do not change and need only to be
recompiled with a corresponding OS/390 compiler. However, consideration
should also be given to the fact that certain application level interfaces available
in VSE may not be available in OS/390. The macro level API is one example.
Applications written with this interface will have to be changed to use the
command level API. Any access to system level control blocks should also be
reviewed. Additional considerations will be required if the CICS application
programs are interfacing with more than the CICS subsystem. Also, there are
some source language restrictions. This document contains a section describing
the CICS, DB2 and DL/I subsystems in great detail.
In summary, when comparing online and batch programs, the effort required to
convert batch applications is much greater than online applications using
application subsystems such as CICS and DL/I. By using application subsystems
the differences in control program application interfaces become transparent to
the application programmer. The installation only needs to be concerned with
the common interface provided by the subsystem in situations where a VSE
version and an OS/390 version are both available.
convert batch applications is much greater than online applications using
application subsystems such as CICS and DL/I. By using application subsystems
the differences in control program application interfaces become transparent to
the application programmer. The installation only needs to be concerned with
the common interface provided by the subsystem in situations where a VSE
version and an OS/390 version are both available.
2.1.2.2 Job Control Language
All VSE JCL must be converted to OS/390 JCL. Because VSE and OS/390 differ
significantly in JCL structure and syntax, this is normally one of the most
complex tasks of any migration. As in the case of batch and online source
programs, the considerations are more significant with the batch applications.
There are, however, aids available to reduce the effort required.
significantly in JCL structure and syntax, this is normally one of the most
complex tasks of any migration. As in the case of batch and online source
programs, the considerations are more significant with the batch applications.
There are, however, aids available to reduce the effort required.
2.1.2.3 Files
The impact of file conversion can be reduced by positioning the VSE production
system with file formats and access methods that are compatible with both VSE
and OS/390.
system with file formats and access methods that are compatible with both VSE
and OS/390.
VSAM files are generally compatible files. One section of this document is
dedicated exclusively to VSAM files and VSAM catalogs. Additional information
regarding VSAM file considerations can be found in the different source
language sections.
dedicated exclusively to VSAM files and VSAM catalogs. Additional information
regarding VSAM file considerations can be found in the different source
language sections.
Direct Access Method (DAM) files require individual evaluation because each
can have unique characteristics. Each of the language sections has a description
on accessing DAM files. It is recommended that these file structures be
converted to relative record VSAM files where possible.
can have unique characteristics. Each of the language sections has a description
on accessing DAM files. It is recommended that these file structures be
converted to relative record VSAM files where possible.
Sequential tape files are compatible between VSE and OS/390. There can be
differences in the format of the labels and how they are processed. There is a
chapter in this publication that deals exclusively with tape files.
differences in the format of the labels and how they are processed. There is a
chapter in this publication that deals exclusively with tape files.
Chapter 2. Sizing the Effort
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