Joohyung Yun

윤주형 · Ph.D. student, Data Systems Lab, POSTECH

Retrieval that reasons over text, tables, and images.

multimodal document RAGagentic retrievalmultihop QA
POSTECH · Pohang, Korea

About

advised by Wook-Shin Han

I am a fourth-year integrated M.S./Ph.D. student (second year of the Ph.D.) in Computer Science at POSTECH, advised by Prof. Wook-Shin Han in the Data Systems Lab. I work where natural language processing meets information retrieval: retrieval-augmented generation over complex, real-world documents that mix text, tables, and images.

My recent work treats retrieval as something an agent does rather than a single lookup: traversing document structure, noticing when a path fails, and backtracking with that feedback. Next, I want these systems to be trustworthy at enterprise scale: verifiable answers over knowledge graphs and multimodal corpora.

Research

3 directions
Multimodal multihop retrievalFinding evidence scattered across the text, tables, and images of many documents, at the right granularity.LILaC · HELIOS
Agentic document RAGAgents that traverse document structure, detect a failed path, and backtrack using that failure as feedback.FiF · ongoing
Structured & enterprise dataSchema discovery, knowledge graphs, and verifiable answers over heterogeneous enterprise data.ReCG · CRAG

News

10 items

Publications

5 papers · scholar ↗
ICML 2026

Failure is Feedback: History-Aware Backtracking for Agentic Traversal in Multimodal Graphs

Yun, J., Lee, D., Han, W.
summary

Agentic retrieval over multimodal documents must commit to a path without exploring every alternative. FiF treats a failed step as feedback: it backtracks to the last decision point and uses the failure to choose a different branch, reaching state-of-the-art accuracy on MultimodalQA, MMCoQA, and WebQA at lower cost.

Failure is Feedback: History-Aware Backtracking for Agentic Traversal in Multimodal Graphs overview
EMNLP 2025

LILaC: Late Interacting in Layered Component Graph for Open-domain Multimodal Multihop Retrieval

Yun, J., Lee, D., Han, W.
summary

LILaC indexes a document collection as a two-layer component graph: a coarse layer for fast candidate generation and a fine layer for reasoning across text, tables, and images. A late-interaction traversal retrieves the relevant subgraph, improving both precision and recall on multihop queries.

LILaC: Late Interacting in Layered Component Graph for Open-domain Multimodal Multihop Retrieval overview
ACL 2025

HELIOS: Harmonizing Early Fusion, Late Fusion, and LLM Reasoning for Multi-Granular Table-Text Retrieval

Park, S., Yun, J., Lee, J., Han, W.
summary

Early fusion pre-aligns tables with passages and over-retrieves; late fusion aligns on the fly and under-retrieves. HELIOS combines both over a layered graph and adds an LLM reasoning step, giving higher retrieval accuracy on table-text benchmarks with efficient inference.

HELIOS: Harmonizing Early Fusion, Late Fusion, and LLM Reasoning for Multi-Granular Table-Text Retrieval overview
PVLDB 2024

ReCG: Bottom-Up JSON Schema Discovery Using a Repetitive Cluster-and-Generalize Framework

Yun, J., Tak, B., Han, W.
summary

Top-down schema discovery decides a node's type before seeing its children and gets heterogeneous data wrong. ReCG works bottom-up, clustering leaf patterns and generalizing upward under a minimum-description-length objective, improving schema accuracy by up to 47% while running faster than prior methods.

ReCG: Bottom-Up JSON Schema Discovery Using a Repetitive Cluster-and-Generalize Framework overview
KDD Cup 2024 · RAG Workshop

KDD Cup Meta CRAG 2024 Technical Report: Three-Step Question-Answering Framework

Park, S., Seok, J., Lee, J., Yun, J., Lee, W.
summary

A three-step framework for the Meta CRAG challenge: answer from parametric knowledge when it suffices, retrieve external evidence only when needed, and verify the generated answer before returning it, cutting hallucination while keeping retrieval cost low.

KDD Cup Meta CRAG 2024 Technical Report: Three-Step Question-Answering Framework overview

Talks

5 decks · all talks ↗

Seminars

10 decks · all seminars ↗
2026-10-14
ReCG — Worked Example
ReCG · PVLDB 2024 · Worked Example Discovering a JSON schema from the leaves up ReCG infers a set of JSON schemas from documents alone. It r…
2026-10-14
LILaC — Worked Example
LILaC · EMNLP 2025 · Worked Example How a question about a photo two hops away gets answered LILaC retrieves from documents that mix paragra…
2026-06-03
Failure is Feedback — Worked Example
Failure is Feedback · Worked Example How a failed hop becomes re-planning feedback A multi-hop retrieval agent walks a document graph one ho…

Experience

Teaching

2024
TA · Design of Digital Systems (CSED273)
POSTECH
2022
TA · Advanced Machine Learning
Samsung Electronics × Data Systems Lab
2021
TA · Data Processing, Distributed DB & Deep Learning
Samsung Electronics × Data Systems Lab

Honors & Patents

Awards
2026
Overseas Dispatch Program for Graduate Students (long-term) · POSTECH
2025
Research Excellence Award · POSTECH
2025
CSE Outstanding Paper Award · POSTECH
2025
BK POSTECHIAN Fellowship · BK21
2024
1st place, comparison & post-processing tests · KDD Cup 2024 Meta CRAG
2021
National Science & Technology Scholarship · Korea
2021
Global Leadership Program Scholarship · POSTECH
2020
Global Leadership Program Scholarship · POSTECH
Patents
Subgraph Retrieval System Based on Layered Component Graph for Open-Domain Multimodal Document Retrieval
KR 10-2025-0195617 · Han, W., Yun, J.
Apparatus and Method for Table and Document Retrieval Based on Questions
PCT/KR2025/003037 · Han, W., Park, S., Yun, J., Lee, J.
AI Technology for Predicting On-site Safety Accidents in Hazardous Chemical Facilities
KR 10-2024-0167340 · Han, W., Ha, J., Yun, J.

Education

2023 –
Integrated M.S./Ph.D., Computer Science · POSTECH
Data Systems Lab · advisor Prof. Wook-Shin Han
2019 – 2023
B.S., Computer Science · POSTECH
summa cum laude · GPA 4.11 / 4.30
2016 – 2019
Hyundai Chungun High School
Languages
Korean (native) · English (fluent) · Japanese (fluent)