CICS Transaction Mapping: Using Visual Reverse Engineering to Document Mainframe Flows

The $3.6 trillion technical debt crisis isn't found in modern microservices; it’s hidden in the CICS transaction logs of mainframes that haven't been documented since the Clinton administration. In many Tier-1 financial institutions, the only person who understands the core credit card processing logic is a developer named Bob who retired in 2014. When Bob left, the "how" and "why" of the system went with him, leaving behind a "green screen" interface that modern engineers treat like an archaeological site.

CICS transaction mapping using traditional methods is an exercise in futility. It involves manually tracing COBOL source code, deciphering Basic Mapping Support (BMS) macros, and interviewing end-users who have developed "muscle memory" for shortcuts that aren't recorded anywhere. This manual audit process takes an average of 40 hours per screen, contributing to the staggering statistic that 70% of legacy rewrites fail or exceed their timelines.

At Replay, we’ve pioneered a different path: Visual Reverse Engineering. Instead of reading dead code, we record the living system in action.

TL;DR:

• •The Problem: 67% of legacy systems lack documentation, making CICS modernization high-risk.
• •The Solution: Visual Reverse Engineering (VRE) records user workflows to automatically generate React code and documentation.
• •Efficiency: Replay reduces modernization time from 18–24 months to weeks, cutting per-screen effort from 40 hours to 4 hours.
• •Compliance: Built for regulated industries (SOC2, HIPAA, On-Premise available).

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The Documentation Gap: Why CICS Mapping Fails#

According to Replay’s analysis, the primary reason legacy modernization projects stall is the "Documentation Gap." When you look at a CICS (Customer Information Control System) environment, you aren't just looking at code; you're looking at decades of business rules layered like sediment.

Industry experts recommend a "runtime-first" approach to documentation. Static analysis of COBOL files often misses dynamic transaction routing and the complex state transitions that occur within a CICS region. If you rely solely on source code, you miss the user’s actual workflow—the "hidden" steps they take to bypass bugs or handle edge cases.

Video-to-code is the process of capturing these real-time user interactions and programmatically converting the visual output into structured data, component hierarchies, and executable React code.

Modernizing Mainframe UI requires more than just a screen scraper; it requires a deep understanding of how transactions map to modern UI components.

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CICS Transaction Mapping Using Visual Reverse Engineering#

CICS transaction mapping using Replay’s Visual Reverse Engineering (VRE) platform transforms the discovery phase of modernization. Instead of months of "discovery workshops," a business analyst simply records themselves performing a standard workflow—like opening a new commercial loan account—in the 3270 terminal emulator.

How the Replay VRE Pipeline Works#

1. •Capture: The user records a session. Replay captures the visual state, the keystrokes, and the transaction triggers.
2. •Analysis: The AI Automation Suite analyzes the screen transitions. It identifies patterns, such as "Header," "Data Grid," and "Command Line."
3. •Mapping: The platform maps CICS fields (like
   text

   DFHMDF
   ) to modern TypeScript interfaces.
4. •Generation: Replay produces a "Blueprint"—a high-fidelity, documented React component that mirrors the legacy logic but uses modern architecture.

Comparative Efficiency: Manual vs. Replay VRE#

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Technical Implementation: From BMS to React#

To understand the power of cics transaction mapping using Replay, we have to look at the translation layer. A traditional CICS BMS map defines fields in a coordinate-based system (Row/Column).

The Legacy Definition (BMS Macro)#

text
PRINT NOGEN
ACCTMAP  DFHMSD TYPE=&SYSPARM,MODE=INOUT,LANG=COBOL,STORAGE=AUTO
ACCTREC  DFHMDI SIZE=(24,80),LINE=1,COLUMN=1
TITLE    DFHMDF POS=(1,32),LENGTH=15,INITIAL='ACCOUNT DETAILS',        *
               ATTRB=(ASKIP,BRT)
LABEL1   DFHMDF POS=(3,1),LENGTH=10,INITIAL='ACCT NO:'
ACCTINP  DFHMDF POS=(3,12),LENGTH=8,ATTRB=(UNPROT,IC)
         DFHMSD TYPE=FINAL
END

In a manual rewrite, a developer would have to read this, understand the

(attributes) for protection and brightness, and then manually create a form in React. Using Replay, this is automatically converted into a structured TypeScript interface and a functional component.

The Modernized Replay Output (React + TypeScript)#

Replay doesn't just give you a "look-alike" screen. It generates a documented component library that follows your enterprise design system.

typescript
// Generated by Replay Blueprints
import React from 'react';
import { TextField, Typography, Box } from '@your-org/design-system';

interface AccountDetailsProps {
  accountNumber: string;
  onTransactionSubmit: (data: string) => void;
  isReadOnly?: boolean;
}

/**
 * Modernized CICS Transaction: ACCTREC
 * Original Map: ACCTMAP
 * Description: Primary account detail view for commercial banking flow.
 */
export const AccountDetails: React.FC<AccountDetailsProps> = ({
  accountNumber,
  onTransactionSubmit,
  isReadOnly = false,
}) => {
  return (
    <Box className="p-6 bg-white shadow-md rounded-lg">
      <Typography variant="h1" className="text-center mb-4">
        ACCOUNT DETAILS
      </Typography>
      
      <Box className="flex items-center gap-4">
        <label htmlFor="acctInp" className="font-bold">ACCT NO:</label>
        <TextField
          id="acctInp"
          value={accountNumber}
          disabled={isReadOnly}
          onChange={(e) => onTransactionSubmit(e.target.value)}
          variant="outlined"
        />
      </Box>
    </Box>
  );
};

This component is now part of your Replay Library, where it can be managed as a reusable asset.

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Mapping Complex State Flows#

CICS transactions are rarely single-page events. They are "flows"—sequences of screens where data is passed via the COMMAREA (Communication Area). CICS transaction mapping using Replay captures these flows visually.

When a user moves from an "Account Summary" screen to "Transaction History," Replay’s Flows feature creates a state machine diagram. This visualizes the architecture of the legacy system without requiring you to trace the

or commands in the COBOL source.

Visualizing the State Machine#

By recording multiple paths through the mainframe, Replay identifies:

• •Primary Success Paths: The standard way a transaction is completed.
• •Error Branches: What happens when a user enters an invalid ID (e.g., the screen returns a red "INVALID ACCT" message).
• •Hidden Dependencies: Screens that must be visited to "prime" the system state.

According to Replay's analysis, capturing these "branching" behaviors accounts for 50% of the total modernization effort. Automating this discovery saves hundreds of hours in the QA phase.

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Why Regulated Industries Choose Replay#

For Financial Services, Healthcare, and Government sectors, "moving fast" cannot come at the expense of security. The technical debt in these industries is often tied to systems that handle PII (Personally Identifiable Information) or PHI (Protected Health Information).

Replay is built for these high-stakes environments:

• •SOC2 & HIPAA Ready: Our platform adheres to the strictest data handling standards.
• •On-Premise Deployment: For organizations that cannot let their mainframe data leave their internal network, Replay offers a fully air-gapped on-premise solution.
• •PII Redaction: Our AI Automation Suite includes automated masking, ensuring that sensitive data recorded during the mapping process is redacted before it enters the documentation library.

Automated Documentation Guide explains how these security layers integrate directly into the reverse engineering pipeline.

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Accelerating the "Big Iron" Modernization#

The average enterprise rewrite timeline is 18 months. By cics transaction mapping using Replay, organizations have seen this timeline shrink to just a few weeks of active work.

Industry experts recommend focusing on the "Componentization" of the mainframe. Instead of a monolithic "Big Bang" migration, use Replay to extract specific high-value flows—like "Customer Onboarding"—and turn them into a modern React-based micro-frontend.

Implementing Replay in Your Architecture#

1. •Identify the Core Flows: Use Replay to record the top 20% of transactions that handle 80% of the business volume.
2. •Generate the Design System: Use the Library feature to extract common UI patterns from the green screens and map them to your modern Design System.
3. •Refine in Blueprints: Use the Blueprints editor to tweak the generated React code, ensuring it meets your internal coding standards.
4. •Deploy & Iterate: Push the documented, modern components to your new cloud-native front-end.

typescript
// Example of a Replay-generated Flow Controller
import { useFlowState } from '@replay-build/runtime';

export const MainframeFlowController = () => {
  const { currentStep, next, previous } = useFlowState('LOAN_ORIGINATION');

  return (
    <div>
      {currentStep === 'SEARCH' && <AccountSearch onNext={next} />}
      {currentStep === 'DETAILS' && <AccountDetails onNext={next} onBack={previous} />}
      {currentStep === 'CONFIRM' && <TransactionConfirm onConfirm={next} />}
    </div>
  );
};

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The Economics of Visual Reverse Engineering#

Let’s look at the numbers. If an enterprise has 500 legacy screens (a modest estimate for a mainframe environment):

• •Manual Mapping: 500 screens x 40 hours = 20,000 man-hours. At $100/hr, that is a $2,000,000 discovery cost with high risk of inaccuracy.
• •Replay Mapping: 500 screens x 4 hours = 2,000 man-hours. At $100/hr, that is a $200,000 discovery cost.

The 70% average time savings isn't just a marketing figure; it's the result of removing the manual "translation" layer between the legacy screen and the modern code.

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Frequently Asked Questions#

What is CICS transaction mapping using Visual Reverse Engineering?#

It is a modernization methodology where user interactions with legacy mainframe screens (3270 terminals) are recorded and automatically converted into documented React components, flow diagrams, and TypeScript interfaces. This replaces manual code analysis with automated visual discovery.

Does Replay require access to my COBOL source code?#

No. Replay’s Visual Reverse Engineering works by observing the runtime behavior and the visual output of the system. While it can be augmented with source code, it is designed to document and modernize systems where documentation is missing or the source code is too complex to trace manually.

How does Replay handle PII during the recording process?#

Replay includes an AI-powered redaction engine specifically built for regulated industries like Healthcare and Finance. It automatically identifies and masks sensitive data patterns (like Social Security numbers or credit card info) during the capture phase, ensuring your Library remains compliant with SOC2 and HIPAA.

Can Replay generate code that matches our internal Design System?#

Yes. Through the Library and Blueprints features, you can map legacy UI elements to your specific enterprise React components. Replay doesn't just output generic HTML; it outputs high-quality TypeScript that utilizes your existing component library.

Is Replay available for on-premise installation?#

Yes. We understand that mainframe data is often the "crown jewels" of an organization. Replay offers an on-premise deployment model that allows the entire Visual Reverse Engineering pipeline to run within your secure data center.

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Ready to modernize without rewriting? Book a pilot with Replay and see how we can turn your legacy CICS flows into modern React components in days, not years.