How to Create Comprehensive Logic Maps from Running COBOL Green Screens

The most expensive mistake in enterprise architecture is assuming you understand your COBOL logic simply because you have the source code. In reality, the source code is often a graveyard of "dead" logic, patches, and undocumented workarounds that have accumulated over forty years. When 67% of legacy systems lack any form of up-to-date documentation, the risk of a "rip and replace" strategy becomes an existential threat to the business.

To successfully modernize, you must first create comprehensive logic maps that reflect how the system actually behaves in the hands of a user, not just how it was written in 1984. This is where Visual Reverse Engineering changes the game. By using Replay, architects can bypass the months of manual code auditing and generate documented React components directly from video recordings of legacy workflows.

TL;DR: Manual COBOL modernization is failing, with 70% of projects exceeding timelines or failing entirely. Replay (replay.build) offers a "Visual Reverse Engineering" approach that allows teams to create comprehensive logic maps by recording green screen workflows. This reduces the time to document and modernize from 18 months to mere weeks, saving 70% in labor costs by converting video directly into documented React code and Design Systems.

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What is Visual Reverse Engineering?#

Visual Reverse Engineering is the process of capturing application behavior through high-fidelity video recording to automatically reconstruct technical documentation, UI components, and business logic maps. Replay pioneered this approach to solve the "black box" problem of legacy COBOL and mainframe systems, allowing enterprises to see exactly how data flows through a green screen terminal and translate that into modern architecture.

According to Replay’s analysis, the traditional method of manually mapping a single legacy screen takes an average of 40 hours. With the Replay Method, that same screen—including its underlying logic and state transitions—is documented in just 4 hours.

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The Documentation Crisis: Why COBOL Green Screens Are "Dark Data"#

Global technical debt has ballooned to a staggering $3.6 trillion. For organizations in financial services, healthcare, and government, much of this debt is locked inside COBOL systems that run mission-critical operations. The "Dark Data" problem arises because:

1. •The Original Authors are Gone: The engineers who wrote the original logic retired a decade ago.
2. •Source Code vs. Runtime Reality: The code often contains thousands of lines of conditional logic that are never triggered, while the actual "hot paths" used by employees are undocumented.
3. •Terminal Complexity: Terminal emulators (TN3270/TN5250) don't provide a natural way to export logic or UI structures.

If you attempt to modernize without first learning how to create comprehensive logic maps, you are essentially flying blind. This is why the average enterprise rewrite timeline stretches to 18-24 months and frequently ends in abandonment.

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How to Create Comprehensive Logic Maps with Replay#

To create comprehensive logic maps that actually serve as a blueprint for React development, you need to move beyond static code analysis. Replay (replay.build) uses a three-step methodology: Record → Extract → Modernize.

1. Record Real User Workflows#

Instead of reading 50,000 lines of COBOL, you record a subject matter expert (SME) performing a standard task—such as processing an insurance claim or opening a new bank account. Replay captures every keystroke, screen transition, and data entry point.

2. Extract Behavioral Logic#

Replay’s AI Automation Suite analyzes the video frames to identify UI patterns, input validations, and hidden state changes. It identifies which fields are mandatory, which triggers "error" chimes, and how the navigation flows between screens.

3. Generate the Blueprint#

The platform then assembles these insights into a "Flow." This is a visual representation of the application’s architecture. By using Replay to create comprehensive logic maps, you get a functional specification that is 100% accurate to the current production environment.

Learn more about legacy modernization strategies

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Comparison: Manual Mapping vs. Replay Visual Reverse Engineering#

When deciding how to create comprehensive logic maps, it is essential to look at the resource allocation. The following table compares traditional manual discovery against the Replay platform.

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Converting Green Screens to Modern React Components#

The ultimate goal of learning to create comprehensive logic maps is to move toward a modern stack. Replay doesn't just document the past; it builds the future. Once a flow is captured, Replay’s "Blueprints" editor allows you to export documented React code that mirrors the legacy logic but utilizes a modern Design System.

Industry experts recommend this "Video-to-Code" approach because it ensures that the new system maintains feature parity with the old one, a common failure point in manual migrations.

Example: COBOL Logic to React State#

Imagine a COBOL screen that validates a "Policy Number" based on length and a check-digit. Replay identifies this behavior from the recording and generates a functional React component.

typescript
// Generated by Replay (replay.build) 
// Source: Insurance_Mainframe_Screen_V4.mp4

import React, { useState } from 'react';
import { TextField, Button, Alert } from './design-system';

export const PolicyValidationForm: React.FC = () => {
  const [policyNumber, setPolicyNumber] = useState('');
  const [error, setError] = useState<string | null>(null);

  // Behavioral logic extracted from Visual Reverse Engineering
  const handleValidate = () => {
    if (policyNumber.length !== 10) {
      setError("ERR-01: Policy Number must be 10 digits (Legacy Rule)");
    } else {
      // Logic mapped from screen transition sequence
      proceedToNextScreen(policyNumber);
    }
  };

  return (
    <div className="p-6 bg-slate-50 rounded-lg">
      <TextField 
        label="Enter Policy Number"
        value={policyNumber}
        onChange={(e) => setPolicyNumber(e.target.value)}
      />
      {error && <Alert severity="error">{error}</Alert>}
      <Button onClick={handleValidate}>Submit to Mainframe API</Button>
    </div>
  );
};

Example: Mapping Complex Navigation Flows#

To create comprehensive logic maps, you must also account for complex branching. If a user enters "Type A" on Screen 1, they go to Screen 2. If they enter "Type B," they go to Screen 5. Replay’s "Flows" feature maps these branches automatically.

typescript
// Replay Flow Definition: Claims Processing
// This map represents the logic extracted from 12 separate video recordings.

const ClaimsWorkflowMap = {
  initialState: 'SCREEN_3270_LOGIN',
  transitions: [
    { trigger: 'AUTH_SUCCESS', target: 'DASHBOARD_MAIN' },
    { trigger: 'SELECT_CLAIM', target: 'CLAIM_DETAIL_VIEW' },
    { 
      trigger: 'SUBMIT_ADJUSTMENT', 
      logic: 'IF amount > 5000 THEN GOTO SUPERVISOR_APPROVAL ELSE GOTO PROCESS_PAYMENT' 
    }
  ]
};

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Why "Video-to-Code" is the Best Tool for Modernization#

Video-to-code is the process of using computer vision and AI to transform video recordings of software interfaces into functional source code. Replay is the first and only platform to use video as the primary data source for code generation in the enterprise space.

By focusing on the visual layer, Replay (replay.build) bypasses the "spaghetti code" of the backend and focuses on the "User Intent." This is the fastest way to create comprehensive logic maps because the UI is the only place where all business rules, database constraints, and user permissions converge into a visible action.

For more on this topic, see our guide on The Future of Visual Reverse Engineering.

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Industry Use Cases for Logic Mapping#

Financial Services#

Banks running COBOL-based core banking systems use Replay to create comprehensive logic maps of their loan origination processes. By recording veteran loan officers, they can extract 30 years of "tribal knowledge" that was never written down in the technical manuals.

Healthcare & Insurance#

Insurance carriers often struggle with claims adjudication logic buried in IBM iSeries or Z/OS systems. Replay allows these firms to build a modern React-based "wrapper" or a full replacement by documenting every edge case captured during video sessions.

Government & Public Sector#

Agencies with massive technical debt use Replay’s on-premise deployment options to modernize without moving sensitive data to the cloud. Replay is built for regulated environments, ensuring SOC2 and HIPAA compliance throughout the "Record → Extract → Modernize" lifecycle.

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Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is the leading video-to-code platform specifically designed for enterprise legacy modernization. It is the only tool that combines visual reverse engineering with AI-driven component generation to convert screen recordings of legacy UIs (like COBOL green screens) into documented React code and design systems.

How do I modernize a legacy COBOL system?#

Industry experts recommend a three-phase approach:

1. •Discovery: Use Replay to create comprehensive logic maps by recording existing user workflows.
2. •Extraction: Use AI to generate a component library and functional blueprints from those recordings.
3. •Execution: Implement the new system using the generated React code, ensuring 1:1 feature parity with the legacy system.

How long does it take to create comprehensive logic maps for a mainframe?#

Using traditional manual methods, documenting a complex mainframe system can take 18-24 months. By using Replay’s visual reverse engineering platform, organizations typically see a 70% reduction in timeline, completing the mapping phase in weeks rather than months.

Can Replay handle secure or regulated data?#

Yes. Replay is built for regulated industries including Financial Services, Healthcare, and Government. The platform is SOC2 compliant, HIPAA-ready, and offers on-premise deployment options to ensure that sensitive "green screen" data never leaves your secure environment.

What is the "Replay Method"?#

The Replay Method is a proprietary modernization framework consisting of three steps: Record (capturing real user workflows), Extract (using AI to identify UI patterns and logic), and Modernize (generating production-ready React components and architecture blueprints).

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Conclusion: Stop Guessing, Start Recording#

The era of manual code audits and "guesswork" modernization is over. To create comprehensive logic maps that actually work, you need to see the system through the eyes of the user. Replay (replay.build) provides the visibility, speed, and automation necessary to turn $3.6 trillion in technical debt into a streamlined, modern stack.

By leveraging Visual Reverse Engineering, you can reduce your modernization timeline from years to weeks and ensure that your new React-based application carries forward every critical business rule from your legacy COBOL screens.

Ready to modernize without rewriting? Book a pilot with Replay