Journal Publication 

1. Reachability Problems in Low-dimensional Nondeterministic Polynomial Maps over Integers, Sang-Ki Ko, Reino Niskanen and Igor Potapov, To appear in Information and Computation (I&C)

2. Generalizations of Code Languages with Marginal Errors, Sang-Ki Ko, Yo-Sub Han and Kai Salomaa, To appear in International Journal of Foundations of Computer Science (IJFCS)

3. Left is Better Than Right for Reducing Nondeterminism of NFA, Sang-Ki Ko and Yo-Sub Han, To appear in International Journal of Foundations of Computer Science (IJFCS)

4. Closest Substring Problems for Regular Languages, Yo-Sub Han, Sang-Ki Ko, Timothy Ng and Kai Salomaa, To appear in Theoretical Computer Science (TCS)

5. Consensus String Problem for Multiple Regular Languages, Yo-Sub Han, Sang-Ki Ko, Timothy Ng and Kai Salomaa, To appear in Information and Computation (I&C)

6. Alignment Distance of Regular Tree Languages, Yo-Sub Han and Sang-Ki Ko, In Theoretical Computer Science, Vol. 787, 127--137, October 2019

7. Neural Sign Language Translation Based on Human Keypoint Estimation, Sang-Ki Ko, Chang Jo Kim, Hyedong Jung and Choongsang Cho, In Applied Sciences Vol. 9, No. 13, July 2019

8. Top-down tree edit-distance of regular tree languages, Sang-Ki Ko, Yo-Sub Han and Kai Salomaa, In International Journal of Advances in Engineering Sciences and Applied Mathematics Vol. 11, Num. 1, 2--10, 2019

9. Vector Ambiguity and Freeness Problems in SL(2, ℤ), Sang-Ki Ko and Igor Potaov, In Fundamenta Informaticae (FI) Vol. 162, 161--182, Aug. 2018

10. State Complexity of k-Parallel Tree Concatenation, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Fundamenta Informaticae (FI) Vol. 154, 185--199, Aug. 2017

11. State Complexity of Permutation on Finite Languages over a Binary Alphabet, Da-Jung Cho, Daniel Goc, Yo-Sub Han, Sang-Ki Ko, Alexandros Palioudakis and Kai Salomaa, In Theoretical Computer Science (TCS) Vol. 682, 67--78, June 2017

12. State Complexity of Regular Tree Languages for Tree Matching, Sang-Ki Ko, Ha-Rim Lee and Yo-Sub Han, In International Journal of Foundations of Computer Science (IJFCS) Vol. 27, No. 8 965--979, December 2016 

13. State Complexity of Insertion, Yo-Sub Han, Sang-Ki Ko, Timothy Ng and Kai Salomaa, In International Journal of Foundations of Computer Science (IJFCS) Vol. 27, No. 7 863--878, November 2016 

14. Operational State Complexity of Subtree-Free Regular Tree Languages, Sang-Ki Ko, Hae-Sung Eom and Yo-Sub Han, In International Journal of Foundations of Computer Science (IJFCS) Vol. 27, No. 6 705--724, September 2016 

15. Approximate Matching between a Context-Free Grammar and a Finite-State Automaton, Sang-Ki Ko, Yo-Sub Han and Kai Salomaa, In Information and Computation (I&C), Vol. 247, 278--289, April 2016 

16. State Complexity of Inversion Operations, Da-Jung Cho, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Theoretical Computer Science (TCS), Vol. 610, 2--12, January 2016 

17. State complexity of deletion and bipolar deletion, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Acta Informatica, Vol. 53, 67--85, February 2016 

18. Pseudo-inversion: closure properties and decidability, Da-Jung Cho, Yo-Sub Han, Shin-Dong Kang, Hwee Kim, Sang-Ki Ko and Kai Salomaa, In Natural Computing, Vol. 15, 31--39, March 2016 

19. State complexity of Kleene-star operations on regular tree languages, Yo-Sub Han, Sang-Ki Ko, Xiaoxue Piao and Kai Salomaa, In Acta Cybernetica Vol. 22(2), 403--422, November 2015 

20. Decidability of involution hypercodes, Da-Jung Cho, Yo-Sub Han and Sang-Ki Ko, In Theoretical Computer Science (TCS), Vol. 550, 90--99, September 2014 

21. The Edit-Distance between a Regular Language and a Context-Free Language, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In International Journal of Foundations of Computer Science (IJFCS), Vol. 24, No. 7, 1067--1082, November 2013 

22. Analysis of a cellular automaton model for car traffic with a junction, Yo-Sub Han and Sang-Ki Ko, In Theoretical Computer Science (TCS), Vol. 450, 54--67, September 2012 

23. A Movie Recommendation Algorithm based on Genre Correlations, Sang-Min Choi, Sang-Ki Ko and Yo-Sub Han, In Expert Systems with Applications, Vol. 39, 8079--8085, July 2012 

Conference Presentations

1. Ball Trajectory Inference from Multi-Agent Sports Contexts Using Set Transformer and Hierarchical Bi-LSTM, Hyunsung Kim, Han-Jun Choi, Chang Jo Kim, Jinsung Yoon and Sang-Ki Ko, accepted at KDD 2023 (BK21 Top Conference, IF: 4)

2. Existential and Universal Width of Alternating Finite Automata, Yo-Sub Han, Sungmin Kim, Sang-Ki Ko and Kai Salomaa, accepted at DCFS 2023

3. On the Simon’s Congruence Neighborhood of Languages, Sungmin Kim, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, accepted at DLT 2023

4. Automated Grading of Regular Expressions, Su-Hyeon Kim, Youngwook Kim, Yo-Sub Han, Hyeonseung Im and Sang-Ki Ko, accepted at ESOP 2023 (BK21 Top Conference, IF: 2)

5. Simon’s Congruence Pattern Matching, Sungmin Kim, Sang-Ki Ko, Yo-Sub Han, ISAAC 2022 (BK21 Top Conference, IF: 1)

6. On Simon’s Congruence Closure of a String, Sungmin Kim, Kai Salomaa, Yo-Sub Han and Sang-Ki Ko, accepted at DCFS 2022

7. SoccerCPD: Formation and role change-point detection in soccer matches from spatiotemporal tracking data, Hyunsung Kim, Bit Kim, Dongwook Chung, Jinsung Yoon and Sang-Ki Ko, accepted at KDD 2022 (BK21 Top Conference, IF: 4)

8. RepCoder: An Automated Program Repair Framework for Probability-Based Program Synthesis, Suhwan Ji, Sang-Min Choi, Sang-Ki Ko, Dohyung Kim, Hyeunseung Lim, accepted at SAC 2022 (BK21 Top Conference, IF: 1)

9. 6MapNet: Representing Soccer Players from Tracking Data by a Triplet Network, Hyunsung Kim, Jihun Kim, Dongwook Chung, Jonghyun Lee, Jinsung Yoon and Sang-Ki Ko, accepted at MLSA@PKDD/ECML 2021

10. Most Pseudo-copy Languages Are Not Context-free, Hyunjoon Cheon, Joonghyuk Hahn, Yo-Sub Han and Sang-Ki Ko, accepted at COCOON 2021

11. Efficient Enumeration of Regular Expressions for Faster Regular Expression Synthesis, Su-Hyeon Kim, Hyeonseung Im and Sang-Ki ko, accepted at CIAA 2021

12. SALNet: Semi-supervised Few-Shot Text Classification with Attention-based Lexicon Construction, Ju-Hyoung Lee, Sang-Ki Ko and Yo-Sub Han, accepted at AAAI 2021 (BK21 Top Conference, IF: 4)

13. The Relative Edit-Distance Between Two Input-Driven Languages, Hyunjoon Cheon, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, accepted at DLT 2019

14. Limited Nondeterminism of Input-Driven Pushdown Automata: Decidability and Complexity, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, accepted at DCFS 2019

15. Reachability Problems in Nondeterministic Polynomial Maps on the Integers, Sang-Ki Ko, Reino Niskanen and Igor Potapov, In Proceedings of the 22nd International Conference on Developments in Language Theory (DLT 2018), LNCS 11088, 465--477, 2018

16. Closest Substring Problems for Regular Languages, Yo-Sub Han, Sang-Ki Ko, Timothy Ng and Kai Salomaa, In Proceedings of the 22nd International Conference on Developments in Language Theory (DLT 2018), LNCS 11088, 392--403, 2018

17. On the Identity Problem for the Special Linear Group and the Heisenberg Group, Sang-Ki Ko, Reino Niskanen and Igor Potapov, In Proceedings of the 45th International Colloquium on Automata, Languages, and  Programming (ICALP 2018), LIPICs 132, 1--15, 2018 (BK21 Top Conference, IF: 2)

18. Alignment Distance of Regular Tree Languages, Yo-Sub Han and Sang-Ki Ko, In Proceedings of the 22nd International Conference on Implementation and Application of Automata (CIAA 17), LNCS 10329, 126--137, 2017

19. Vector Ambiguity and Freeness Problems in SL(2,Z), Sang-Ki Ko and Igor Potapov, In Proceedings of the 14th Annual Conference on Theory and Applications of Models of Computation (TAMC 17), LNCS 10185, 373-388, 2017

20. Consensus String Problem for Multiple Regular Languages, Yo-Sub Han, Sang-Ki Ko, Timothy Ng and Kai Salomaa, In Proceedings of the 11th International Conference on Language and Automata Theory and Applications (LATA 17), LNCS 10168, 196--207, 2017

21. Matrix Semigroup Freeness Problems in SL(2,Z), Sang-Ki Ko and Igor Potapov, In Proceedings of the 43rd International Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM 17), LNCS 10139, 268--279, 2017 

22. Edit-Distance between Visibly Pushdown Languages, Yo-Sub Han and Sang-Ki Ko, In Proceedings of the 43rd International Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM 17), LNCS 10139, 387--401, 2017 

23. Inferring a Relax NG Schema from XML Documents, Guen-Hae Kim, Sang-Ki Ko, Yo-Sub Han, In Proceedings of the 10th International Conference on Language and Automata Theory and Applications (LATA 16), LNCS 9618, 400--411, 2016 

24. Generalizations of Code Languages with Marginal Errors, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 19th International Conference on Developments in Language Theory (DLT 15), LNCS 9118, 220--230, 2015 

25. The State Complexity of Permutations on Finite Languages over Binary Alphabets, Alexandros Palioudakis, Da-Jung Cho, Daniel Goc, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 18th In Proceedings of the 17th International Workshop on Descriptional Complexity of Formal Systems (DCFS 15), LNCS 9118, 220--230, 2015 

26. State Complexity of Deletion, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 18th International Conference on Developments in Language Theory (DLT 14), LNCS 8633, 37--48, 2014 

27. State Complexity of Inversion Operations, Da-Jung Cho, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 16th International Workshop on Descriptional Complexity of Formal Systems (DCFS 14), LNCS 8614, 102--113, 2014 

28. State Complexity of Regular Tree Languages for Tree Pattern Matching, Sang-Ki Ko, Ha-Rim Lee and Yo-Sub Han, In Proceedings of the 16th International Workshop on Descriptional Complexity of Formal Systems (DCFS 14), LNCS 8614, 246--257, 2014 

29. Left is Better Than Right for Reducing Nondeterminism of NFAs, Sang-Ki Ko and Yo-Sub Han, In Proceedings of the 19th International Conference on Implementation and Application of Automata (CIAA 14), LNCS 8587, 238--251, 2014 

30. Pseudo-Inversion on Formal Languages, Da-Jung Cho, Yo-Sub Han, Shin-Dong Kang, Hwee Kim, Sang-Ki Ko and Kai Salomaa, In Proceedings of Unconventional Computation & Natural Computation 2014 (UCNC 14), LNCS 8553, 93--104, 2014 

31. Top-Down Tree Edit-Distance of Regular Tree Languages, Sang-Ki Ko, Yo-Sub Han and Kai Salomaa, In Proceedings of the 8th International Conference on Language and Automata Theory and Applications (LATA 14), LNCS 8370, 466--477, 2014 

32. A CA Model for Target Tracking in Distributed Mobile Wireless Sensor Network, Sang-Ki Ko, Hwee Kim and Yo-Sub Han, In Proceedings of the 13th International Conference on Control, Automation and Systems (ICCAS 13), 1356--1361, 2013 

33. State Complexity of Subtree-Free Regular Tree Languages, Hae-Sung Eom, Yo-Sub Han and Sang-Ki Ko, In Proceedings of the 15th International Workshop on Descriptional Complexity of Formal Systems (DCFS 13), LNCS 8031, 66--77, 2013 

34. Approximate Matching between a Context-Free Grammar and a Finite-State Automaton, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 18th International Conference on Implementation and Application of Automata (CIAA 13), LNCS 7982, 146--157, 2013 

35. Computing the edit-distance between a regular language and a context-free language, Yo-Sub Han, Sang-Ki Ko and Kai Salomaa, In Proceedings of the 16th International Conference on Developments in Language Theory (DLT 12), LNCS 7410, 85--96, 2012 

36. A recommendation system based on a subset of raters, Bernhard Scholz, Sang-Min Choi, Sang-Ki Ko, Hae-Sung Eom and Yo-Sub Han, In Proceedings of the 6th International Conference on Ubiquitous Information Management and Communication (ICUIMC 2012), 2012 

37. A Cellular Automaton Model for Car Traffic with a Form-One-Lane Rule, Yo-Sub Han and Sang-Ki Ko, In Proceedings of the 16th International Conference on Implementation and Application of Automata (CIAA 11), LNCS 6807, 154--165, 2011 

38. A Smart Movie Recommendation System, Sang-Ki Ko, Sang-Min Choi, Hae-Sung Eom, Jeong-Won Cha, Hyunchul Cho, Laehyun Kim and Yo-Sub Han, In Proceedings of the HCI International 2011 (HCI 2011), LNCS 6771, 558--566, 2011 

39. Analyzing Category Correlations for Recommendation System, Bernhard Scholz, Sang-Min Choi, Sang-Ki Ko, Hae-Sung Eom and Yo-Sub Han, In Proceedings of the 5th International Conference on Ubiquitous Information Management and Communication (ICUIMC 2011), 2011 

Patents

1. XML SCHEMA TRANSFORMATION METHOD AND DEVICE. Sang-Ki Ko, Yo-Sub Han and Guen-Hae Kim, Registration Number: 1017142700000, 2017. 3. 2.

2. Method and System for Detecting Malicious/Character Sequence Packet Using Regular Expression. Sang-Ki Ko and Yo-Sub Han, Registration Number: 1016458740000, 2016. 7. 29. 

3. Method and Device for Reducing NFA. Sang-Ki Ko, Hae-Sung Eom and Yo-Sub Han, Registration Number: 1016458900000, 2016. 7. 29. 

4. Method and Apparatus for generating automata. Sang-Ki Ko and Yo-Sub Han, Registration Number: 1015839790000, 2016. 1. 4. 

5. Method and Apparatus for controlling form of automata arrangement. Sang-Ki Ko and Yo-Sub Han, Registration Number: 1015839780000, 2016. 1. 4. 

6. AUTOMATA ENCODING DEVICE AND METHOD. Sang-Ki Ko and Yo-Sub Han, Registration Number: 1014886150000, 2015. 1. 26.