Unknown author · 2026 · internet
Literature Survey: Legacy Modernization with Multi-Agent LLMs and Behavioral Specifications
Overview
This survey examines research related to legacy system modernization and identifies key challenges that remain unaddressed by existing work.
Established Research Areas
1. LLM-Based Legacy Modernization
(Generative AI-Driven Legacy System Modernization, 2025) Generative AI enables transformation of monolithic architectures into modern microservices and facilitates code translation, documentation generation, test case creation, and intelligent refactoring recommendations. (Empowering Application Modernization with LLMs, n.d.) Structured frameworks combined with human review processes can modernize legacy applications in contemporary languages like Java and .NET.
However, (Legacy Modernization Using AI Agents, 2026) large language models face significant context limitations—even one-million-token context windows are insufficient for the largest legacy codebases, and tools are largely file- and session-scoped, with understanding lost when sessions end.
2. Multi-Agent Systems for Software Engineering
(AgentMesh, 2025) Software development can require cooperation among multiple members with diverse skills, motivating exploration of agentic frameworks. (Agyn, n.d.) A team-based approach models software engineering as a collaborative process with agents having distinct roles and execution environments. (How Swarms of AI Agents Are, 2026) In practice, multi-agent coordination for debugging workflows achieved a 93% reduction in time-to-root-cause.
3. Program Comprehension and Code Understanding
(Program Comprehension, n.d.) Program comprehension involves top-down and bottom-up processes. (Program Comprehension as a Central Skill, 2025) In the era of generative AI, the critical skill has shifted toward understanding and maintaining AI-generated code. (exa.ai, n.d.) Code understanding challenges include navigation and question-answering.
4. Business Logic Extraction from Legacy Systems
(AgentModernize, n.d.) Business rules in legacy systems are rarely documented—they live in control flow patterns, conditional branches, exception handlers, and configuration files. (Semantic Business Rule Extraction, 2019) Semantic business rule extraction seeks to infer the original intention of procedural logic, complicated by intertwining of technical and business logic. (From COBOL to Models, 2013) Model-driven reverse engineering frameworks extract business logic from legacy COBOL systems.
5. Program Transformation and Semantic Refactoring
(Semantic refactorings, 2017) Syntax-driven refactoring focuses on syntactic transformations, while semantics-driven refactoring uses formal verification to reason over program behavior. (Program synthesis, 2015) Program synthesis can automate refactoring decisions by verifying observational equivalence between original and refactored code.
Critical Research Gaps
Gap 1: Session Persistence and System-Wide Understanding
(Legacy Modernization Using AI Agents, 2026) AI tools operate in session-scoped manner, with understanding lost when sessions end.
Gap 2: Behavioral Correctness During Transformation
(AgentModernize, n.d.) A syntactically correct translation can pass compilation but silently break edge-case handling, alter validation logic, or drop constraints that were never written down.
Gap 3: Behavioral Specification Extraction
(AgentModernize, n.d.) Silent behavioral changes during migration remain a central risk when business rules are not documented.
Gap 4: Large-Scale Codebase Context
(Legacy Modernization Using AI Agents, 2026) Even one-million-token context windows are insufficient for the largest legacy systems spanning hundreds of thousands of files.
Gap 5: API Integration During Code Translation
([2603.14054v1] LegacyTranslate, n.d.) Direct application of LLMs for code translation often produces syntactically valid outputs that fail to compile or integrate within existing production frameworks.
Gap 6: Intermediate Representations for Modernization
[(Software Transformation, n.d.) Program transformation literature discusses representations ranging from source code to intermediate representations to specification.
Conclusion
The surveyed literature shows mature individual techniques for legacy modernization, multi-agent orchestration, program understanding, business logic extraction, and semantic refactoring. Significant challenges remain in integrating these capabilities into systems that maintain behavioral correctness while scaling to large codebases.
Citation Lists
Unknown author · 2025 · internet
Unknown author · 2015 · internet
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