Structured Data and Reasoning Laboratory

Computer Science

Structured Data and Reasoning Laboratory

Fuzzy Systems, Formal Methods, Graph-Based Models, Knowledge Representation, Recurrent Neural Networks

Design and analysis of fuzzy and weighted models for data representation, including automata, networks, Kripke structures, and neural systems

- Fuzzy and weighted automata theory and applications:
Development, analysis, and application of fuzzy and weighted finite-state machines for modeling systems with uncertainty, imprecision, or graded transitions. Special focus on determinization, minimization, and equivalence checking under graded semantics.

- Fuzzy Kripke models and fuzzy modal logics:
Design and analysis of fuzzy Kripke models for representing graded beliefs, preferences, or accessibility relations. Application of fuzzy modal logics to reasoning under uncertainty, especially in formal verification and knowledge systems.

- Modeling and analysis of fuzzy and weighted social networks:
Modeling of social and relational systems using fuzzy graphs and weighted networks. Focus on capturing nuances of intensity, trust, influence, or partial connectivity in real-world networks. Development of similarity measures, partitions, and role detection in such networks.

- Recurrent neural networks with graded and fuzzy inputs:
Integration of fuzzy logic and neural computation for processing sequential or time-dependent data with imprecise or uncertain features. Research includes hybrid symbolic–subsymbolic models and explainable AI methods.

- Semantic representations using quantales and algebraic frameworks:
Use of algebraic and logical frameworks (e.g., quantales, residuated lattices) for the representation and manipulation of structured, uncertain, or fuzzy data. Emphasis on relational models and their decompositions.

• Agreement on the implementation and financing of scientific and research work of the NIO between the Ministry of Education, Science and Technological Development of the Republic of Serbia and the Faculty of Natural Sciences and Mathematics, University of Niš, Grant Number: 451-03-137/2025-03/200124
• Agreement on the implementation and financing of scientific and research work of the NIO between the Ministry of Education, Science and Technological Development of the Republic of Serbia and the Pedagogical Faculty in Vranje, University of Niš, Grant Number: 451-03-137/2025-03/200139

• AMD Ryzen™ Threadripper™ 2920X processor
• NVIDIA GeForce GTX 1080 Ti graphic card

• S. Stanimirović, L. A. Nguyen, M. Ćirić, and M. Stanković, “Breadth‐first fuzzy bisimulations for fuzzy automata,” Fuzzy Sets and Systems, vol. 503, p. 109 246, 2025. DOI: 10.1016/j.fss.2024.109246
• A. G. de Mendívil Grau, S. Stanimirović, and F. Fariña, “Minimal determinization algorithm for fuzzy automata,” IEEE Transactions on Fuzzy Systems, vol. 31, no. 11, pp. 3812–3822, 2023. DOI: 10.1109/TFUZZ.2023.3268406
• I. Micić, S. Stanimirović, and Z. Jančić, “Approximate positional analysis of fuzzy social networks,” Fuzzy Sets and Sys‐ tems, vol. 454, pp. 149–172, 2023. DOI: 10.1016/j.fss.2022.05.008
• M. Stanković, S. Stanimirović, and M. Ćirić, “Approximate Hennessy‐Milner type theorems for fuzzy multimodal log‐ ics over Heyting algebras,” International Journal of Approximate Reasoning, vol. 179, p. 109 362, 2025. DOI: 10.1016/j.ijar.2025.109362
• P.S. Stanimirović, M. Ćirić, S.D. Mourtas, P. Brzaković, D. Karabašević, “Simulations and bisimulations between weighted finite automata based on time-varying models over real numbers,” Mathematics, 2024, 12, 2110. DOI: 10.3390/math12132110

• S. Stanimirović, L. A. Nguyen, M. Ćirić, and M. Stanković, “Breadth‐first fuzzy bisimulations for fuzzy automata,” Fuzzy Sets and Systems, vol. 503, p. 109 246, 2025. DOI: https://doi.org/10.1016/j.fss.2024.109246
• M. Stanković, M. Ćirić, S. Stanimirović, and Đ. Stakić, “Approximate bisimulations for Kripke models of fuzzy multi‐modal logics over complete Heyting algebras,” Fuzzy Sets and Systems, vol. 507, p. 109 299, 2025. DOI: https://doi.org/10.1016/j.fss.2025.109299
• M. Stanković, S. Stanimirović, and M. Ćirić, “Approximate Hennessy‐Milner type theorems for fuzzy multimodal logics over Heyting algebras,” International Journal of Approximate Reasoning, vol. 179, p. 109 362, 2025. DOI: https://doi.org/10.1016/j.ijar.2025.109362
• P.S. Stanimirović, M. Ćirić, S.D. Mourtas, P. Brzaković, D. Karabašević, ”Simulations and bisimulations between weighted finite automata based on time-varying models over real numbers,” Mathematics, 2024, 12, 2110. DOI: https://doi.org/10.3390/math12132110
• M. Ćirić, J. Ignjatović, P. S. Stanimirović, Idempotent-aided factorizations of regular elements of a semigroup, Mathematics, 2024, 12(19), 3136. DOI: https://doi.org/10.3390/math12193136
• A. G. de Mendívil Grau, F. Fariña, S. Stanimirović, I. Micić, and J. R. G. de Mendívil, “Polynomial crisp‐minimization algorithm for fuzzy deterministic automata,” Fuzzy Sets and Systems, vol. 495‐496, p. 109 108, 2024. DOI: https://doi.org/10.1016/j.fss.2024.109108
• I. Micić, S. Stanimirović, J. R. González de Mendívil, M. Ćirić, Z. Jančić, ”Finite determinization of fuzzy automata using a parametric product-based t-norm, ” Fuzzy Sets and Systems, 488, 2024, https://doi.org/10.1016/j.fss.2024.108990
• I. Micić, M. Ćirić, J. Matejić, S. Stanimirović, L. A. Nguyen, Approximate weak simulations and bisimulations for fuzzy automata over the product structure, Fuzzy Sets and Systems, 485, 2024, https://doi.org/10.1016/j.fss.2024.108959
• M. Ćirić, I. Micić, J. Matejić, and A. Stamenković, “Simulations and bisimulations for max-plus automata, ” Discrete Event Dyn Syst, vol. 34, no. 2, pp. 269–295, 2024. DOI: https://doi.org/10.1007/s10626-024-00395-1
• A. G. de Mendívil Grau, S. Stanimirović, and F. Fariña, “Minimal determinization algorithm for fuzzy automata,” IEEE Transactions on Fuzzy Systems, vol. 31, no. 11, pp. 3812–3822, 2023. DOI: https://doi.org/10.1109/TFUZZ.2023.3268406
• L. A. Nguyen, I. Micić, N.‐T. Nguyen, and S. Stanimirović, “Depth‐bounded fuzzy bisimulation for fuzzy modal logic,” Cybernetics and Systems, vol. 0, no. 0, pp. 1–18, 2024. DOI: https://doi.org/10.1080/01969722.2023.2296248
• L. A. Nguyen, I. Micić, and S. Stanimirović, “Fuzzy Minimax Nets,” IEEE Transactions on Fuzzy Systems, vol. 31, no. 8, pp. 2799–2808, 2023. DOI: https://doi.org/10.1109/TFUZZ.2023.3237936
• M. Ćirić, J. Ignjatović, P. S. Stanimirovć, “Outer inverses in semigroups belonging to the prescribed Green’s equivalence classes,“ Semigroup Forum 107 (2023) , 251–293. doi: https://doi.org/10.1007/s00233-023-10382-x
• M. Stanković, M. Ćirić, J. Ignjatović, “Simulations and bisimulations for fuzzy multimodal logics over Heyting algebras,” Filomat, Volume 37, Issue 3, Pages: 711-743, 2023. DOI: https://doi.org/10.2298/FIL2303711S
• X. Cao, A. Fransis, X. Pu, Z. Zhang, V.N. Katsikis, P.S. Stanimirović, I Brajević, S. Li, “A novel recurrent neural network based online portfolio analysis for high frequency trading, ” Expert Systems with Applications, 223 (2023), DOI: https://doi.org/10.1016/j.eswa.2023.120934
• P.S. Stanimirović, B. Ivanov, D. Stanujkić, L.A. Kazakovtsev, V,N, Krutikov, D. Karabašević, “Fuzzy adaptive parameter in the Dai–Liao optimization method based on neutrosophy, ” Symmetry, 2023, 15, 1217. DOI: https://doi.org/10.3390/sym15061217
• I. Micić, L. A. Nguyen, and S. Stanimirović, Characterization and computation of approximate bisimulations for fuzzy automata, Fuzzy Sets and Systems, vol. 442, pp. 331–350, 2022. DOI: https://doi.org/10.1016/j.fss.2022.05.003
• S. Stanimirović, I. Micić, and M. Ćirić, “Approximate bisimulations for fuzzy automata over complete heyting algebras,” IEEE Transactions on Fuzzy Systems, vol. 30, no. 2, pp. 437–447, 2022. DOI: https://doi.org/10.1109/TFUZZ.2020.3039968
• M. Stanković, M. Ćirić, J. Ignjatović, “Hennessy-Milner type theorems for fuzzy multimodal logics over Heyting algebras,“ J. Mult.-Valued Log. Soft Comput. 39 (2--4) (2022) 341--379
• V.N. Katsikis, P.S. Stanimirović, S. Mourtas, L. Xiao, D. Karabašević, D. Stanujkić, “Zeroing Neural Network with fuzzy parameter for computing pseudoinverse of arbitrary matrix,“ IEEE Transactions on Fuzzy Systems 30(9) (2022), 3426-3435. DOI: https://doi.org/10.1109/TFUZZ.2021.3115969
• X. Zhang, L. Chen, S. Li, P.S. Stanimirović, L. Zhang, L. Jin, “Design and analysis of recurrent neural network models with non-linear activation functions for solving time-varying quadratic programming problems,“ CAAI Trans. Intell. Technol. 6(4) (2021), 394-404. DOI: https://doi.org/10.1049/cit2.12019
• S. Stanimirović, M. Ćirić, and J. Ignjatović, “Determinization of fuzzy automata by factorizations of fuzzy states and right invariant fuzzy quasi‐orders,” Information Sciences, vol. 469, pp. 79–100, 2018. DOI: https://doi.org/10.1016/j.ins.2018.08.033
• I. Micić, Z. Jančić, J. Ignjatović and M. Ćirić, "Determinization of Fuzzy Automata by Means of the Degrees of Language Inclusion," in IEEE Transactions on Fuzzy Systems, vol. 23, no. 6, pp. 2144-2153, Dec. 2015, doi: https://doi.org/10.1109/TFUZZ.2015.2404348
• Z. Jančić, M. Ćirić, ”Brzozowski type determinization for fuzzy automata,” Fuzzy Sets and Systems 249 (2014) 73–82. DOI: https://doi.org/10.1016/j.fss.2014.02.021
• A. Stamenković, M. Ćirić, J. Ignjatović, ”Reduction of fuzzy automata by means of fuzzy quasi-orders,” Information Sciences 275 (2014) 168–198. DOI: https://doi.org/10.1016/j.ins.2014.02.028

Members of our research team have been actively involved in numerous national and international projects, focusing on algebraic and automata-theoretic methods in data processing, computation, and modeling.

Selected International Projects:
• Hybrid Methods of Modelling and Optimization in Complex Systems (Russia, 2022–2024, funded by Ministry of Science and Higher Education of the Russian Federation)
• Weighted Pushdown Automata with Different Acceptance Modes (Germany, 2019–2020, DFG – German Research Foundation)
• Theory of Tensors, Operator Matrices and Applications (China–Serbia Bilateral Project, 2018–2020)
• Direct Methods for Digital Image Restoration (North Macedonia–Serbia Bilateral Project, 2014–2017)
• ICT COST Action IC1307 – iV&L Net (2014–2016), a European research network combining computer vision and natural language processing
• Weighted Automata over Semirings and Lattices (Germany–Serbia Bilateral Project, 2009–2010, DAAD & MESTD)
These collaborations enabled the exchange of expertise, joint publications, and researcher mobility between institutions in Serbia, Germany, Russia, China, and North Macedonia.

Selected National Projects with International Relevance:
• QUAM – Quantitative Automata Models: Fundamental Problems and Applications (2022–2024, Science Fund of Serbia), supporting international dissemination and cooperation
• Long-term participation in foundational national projects (1986–2025) funded by the Ministry of Education, Science and Technological Development of Serbia, with outcomes regularly presented in international venues and often developed in cooperation with foreign partners.