Oracle Mainframe Re-hosting Solutions – Part One


This paper provides an overview about Oracle Mainframe Re-hosting solutions from a technical point of view. For people who have little Mainframe background, it adds some mainframe basic concept introduction.

It is targeted to technical people who are interesting in mainframe modernization technology to understand Oracle solution in this area.

This paper will be split into two parts:

  • Part 1: Background for some basic mainframe concepts
  • Part 2: Oracle solution overview (It will be published later in an other blog)

What is Mainframe Re-Hosting?

Re-hosting is one of the options for modernization of Mainframe legacy system.  In the modernization of Mainframe legacy system technology, there are several technical options, according to some common definitions, we can categorize three options:

Re-engineering: A technique to rebuild legacy applications in a new technology or platform, with the same or enhanced functionality, from scratch – usually by adopting Service Oriented Architecture (SOA). From a technical point of view, this is the most efficient and agile way of transforming legacy applications. But, this approach also has more risk from project management, timing and cost.

Package Implementation: Replacement of legacy applications, in whole or part, with commercial off-the-shelf software (COTS) such as ERP, CRM, SCM, Billing software etc.  It is a good solution when such package application can meet the business requirements well.

Re-hosting: Migrate, with some automation tool, the legacy application source code (mainly COBOL) and database , running the legacy applications, with no functional changes, on an Open System platform. This is often used as an intermediate step to eliminate legacy and expensive hardware. Most common examples include mainframe applications being re-hosted on UNIX or “Wintel” platform.

For a typical corporate mainframe customer, the three above options are not mutually exclusive. In reality, a complete modernization plan is often the combination of these options according to different existing software asset analyses and business requirements.

Deciding which options to use to modernization a legacy system is not the subject of this paper.  For that, please refer to the following studies:

This paper will give an overview of Oracle’s Mainframe Re-hosting solution.

Mainframe Legacy Systems

IBM mainframes are large computer systems produced by IBM from 1952 to the present. During the 1960s and 1970s, the term Mainframe was almost synonymous with IBM products due to their market share. Current mainframes in IBM’s line of business computers are developments of the basic design of the IBM System/360.

Operating Systems

The core OS is based on IBM proprietary hardware and software from old DOS, VSE, MVS, MVS/XA, Z/OS, since the 1990s.  On top of Z/OS, IBM has added USS (Unix Service System) and also z/LINUX. But these new OS haven’t had large success; very few mainframe customers have adopted USS and z/Linux for their production system, the majority still run with MVS as the core OS.


Mainly, Mainframes have two major Middleware Products:

  • IMS (Information Management System): IMS is a message based Transaction Processing Management system (TPM) on IBM Mainframe for very large customers.  However since 1990, it has attracted very few new customers. IMS is quite heavy and rigid TPM; it needs a lot of effort to manage it. But it has a solid reputation as a robust TPM.
  • CICS (Customer Information Control System): CICS is another Transaction Processing Management system on IBM mainframe, CICS is middleware designed to support rapid, high-volume online transaction processing. More than 90 % of IBM Mainframe customers are using CICS as middleware.  Compared to IMS, CICS is a more lightweight TPM, initially, it designated to small and middle customers. But today, even big customers are using CICS instead of IMS.


Network is component to manage, configure and monitor all network hardware and software. Today it has two major sub components: SNA and TCP/IP

  • SNA (System Network Architect) is IBM proprietary network technology; it is based on concept PU (Physical Unit) and LU (Logical Unit), and VTAM (Virtual Telecom Access Method).
  • TCP/IP, from 1990’s, IBM was introducing TCP/IP network into IBM Mainframe platform. It is becoming the standard network for IBM mainframe platform.


The Mainframe has several database products:

  • VSAM (Virtual Storage Access Method)  is disk file storage access method.  VSAM comprises fourfile organizations (see below).  Application programs use different organization of VSAM to manage their data.
    • KSDS (Key Sequenced Data Set Key)
    • RRDS (Relative Record Data Set)
    • ESDS (Entry Sequenced Data Set)
    • LDS (Linear Data Set)
  • IMS DB is IMS Database component that stores data using a hierarchical model.  The first IMS DB product started from 1968. Today, there are three options of IMS DB.  These options are used in different business scenarios depending on requirements.
    • Full function databases
    • Fast path databases
    • High Availability Large Databases (HALDBS)
  • DB2 is a major component on IBM Mainframe platform. It was first given to the Database Management System or DBMS in 1983 when IBM released DB2 on its MVS mainframe platform. It is a full relation model database product of IBM.  Today, IBM has brought DB2 to other platforms, including OS/2, UNIX and MS Windows servers, then Linux (including Linux on zSeries) and PDAs.
  • Some third party products, including
    • Natural
    • SUPER Base
    • IDMS2

Batch Execution Environment

During the 1970’s, the OLTP technology was not mature enough to manage data integrity well for On-Line Transaction Processing (OLTP) especially concerning concurrent DB access.  The best practices was to store all DB updates into a temporary file by on-line transaction, then using batch process to update master DB after the on-line transaction closed. To support these practices, IBM mainframe has developed a Batch Execution Infrastructure.

Mainframe has a strong Batch Execution Environment including two major components:

  • JCL (JOB Control Language) is a script language to implement batch process on mainframe. Application developers use it to define their batch process: logic processing, dependencies between multiple steps, error handling, result reporting, etc.
  • JES (Job Entry Subsystem) is one of the major component of MVS system.  It receives jobs into the computer system, schedules them for processing, and controls their output processing.  There are three job entry subsystems in MVS; Master, JES2 and JES3.

Development Environment and Language

Mainframes generally have a 3270 terminal-based development environment.

  • TSO /E (Time Sharing Option/Extensions) allows users to create an interactive session with the MVS system. TSO provides a single-user logon capability and a basic command prompt interface to MVS. It is very like Unix login session.
  • ISPF (Interactive System Productivity Facility), most users work with TSO through ISPF menu-driven interface. This collection of menus and panels offers a wide range of functions to assist users in working with data files on the system.  ISPF users include system programmers, application programmers, administrators, and others who access MVS. In general, TSO and ISPF make it easier for people with varying levels of experience to interact with the MVS system.
  • COBOL is the dominant language for development of applications; More than 95 % of existing mainframe applications were developed with COBOL.
  • PL/I is another application programming language on mainframe. It is a block-structured language, consisting of packages, procedures, statements, expressions, and built-in functions.
  • C, C/++, Since the 1990’s, some customers are using C as application programming language.
  • 4GL languages likes FOCUS, NOMAD
  • Assembly language is used to develop some technical module and exit routine for performance reason
  • Script languages: JCL, REXX, CLIST for Batch JOB, administration, monitoring, etc.

Charging Mode

One particularity interesting feature of IBM mainframe is their software charging mode:

MIPS (Millions Instruction by Second) based charging mode.  Most of IBM mainframe software is charged on this mode.  It means user will be charge by what they consume CPU power. On Open System, most software is are charged by hardware capability.

Current Mainframe Customer Challenges

Some challenges for almost all mainframe customers are:

  • Very high and growing costs
    • Up to 60-80% of IT budget is spent on mainframe legacy systems
    • $2-$5M/year for a 1000 MIPS mainframe
  • Constrained IT Responsiveness
    • All applications have a strong dependency on obsolete technologies
    • High cost of integration and maintenance due to proprietary technologies like SNA network, IMS DB, etc.
    • Difficult to meet new business requirements on time and with allocated budgets
  • Graying mainframe skill base
    • Due to closed,proprietary technology, very few public schools ggive education on these technologies.  It is losing qualified engineers and critical knowledge
  • Rigid IT Infrastructure
    • Complex software layers constrain choices
    • Vendor-driven forced upgrades.  This costs a lot of resources and budget

Market Trend

According to some market studies:

  • Almost all Mainframe customers are thinking, planning, or performing mainframe modernization.
  • A major obstacle is how to find a solution to meet Mainframe RASP  (Robust, Availability, Scalability, Performance.
  • How to make sure of the feasibility of such project

When and Why Re-Hosting

As mainframe customers are evaluating their mainframe modernization strategy, they must take these following points into consideration:

  • Protect investment:  if target software is quite stable, and meets current business requirement, the re-hosting option is a right way to protect investment.
  • Minimize risk: technically, re-hosing is a solution which has minimum risk, because it keeps business logic, data model, user interface almost unchanged.
  • ROI (Return Of Investment):  among all mainframe modernization solutions, very often, re-hosting has a good ROI of whole cost.
  • Progressive Migration:  Re-hosting solutions can make the whole mainframe modernization process progressive.  During whole project period; existing mainframe application, re-hosted application and Open System applications can co-exist and integrate together.    


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