Flora-2 is an open source semantic rule-based system for knowledge representation and reasoning. The language of the system is derived from F-logic,[1] HiLog,[2] and Transaction logic.[3] Being based on F-logic and HiLog implies that object-oriented syntax and higher-order representation are the major features of the system. Flora-2 also supports a form of defeasible reasoning called Logic Programming with Defaults and Argumentation Theories (LPDA).[4] Applications include intelligent agents, Semantic Web, knowledge-bases networking, ontology management, integration of information, security policy analysis, automated database normalization, and more.[5][6][7][8][9][10]

Flora-2 is relying on the XSB system for its inference engine. The design and architecture of Flora-2 are described in a number of works.[11][12][13][14]

Details of the system and its use are described in the Flora-2 User's Manual.[15] Flora-2 is available for all major computing platforms, including Linux and other flavors of Unix, Microsoft Windows (both 32- and 64-bit), and Mac OS X.


Flora-2 is a successor to the Flora system (1998-1999) and incorporates the experience gained developing and using the original Flora system. The Flora-2 project started around year 2000 by Guizhen Yang and Michael Kifer. In later years it was led by Michael Kifer and had many other contributors.

Projects using Flora-2

  • Smart Python Agent Development Environment.
  • TaOPiS is a social semantic Web application for supporting self-organizing communities.[16][17][18]
  • Baze is a database development environment similar to Access and Base.
  • ReasonablePython is a module which adds F-Logic to Python.[19]
  • The FRDCSA project is developing an extension to the Perl XSB interface for supporting access to Flora-2 and HiLog from Perl and the FreeKBS3 system.


  1. M. Kifer, G. Lausen, J. Wu (1995). Foundations of Object-Oriented and Frame-Based Languages, Journal of ACM, May 1995.
  2. W. Chen, M. Kifer and D.S. Warren (1993), HiLog: A Foundation for Higher-Order Logic Programming. Journal of Logic Programming, 1993.
  3. A.J. Bonner and M. Kifer (1993), Transaction Logic Programming, International Conference on Logic Programming (ICLP), 1993.
  4. H. Wan , B. Grosof , M. Kifer , P. Fodor , S. Liang (2009), Logic Programming with Defaults and Argumentation Theories. 25th International Conference on Logic Programming (ICLP 2009), July 2009.
  5. H. Chen, T. Finin, and A. Joshi (2003). An ontology for context-aware pervasive computing environments, The Knowledge Engineering Review 18:3, Cambridge University Press.
  6. Y. Zou, T. Finin, H. Chen (2005). F-OWL: An Inference Engine for Semantic Web, Formal Approaches to Agent-Based Systems, Lecture Notes in Computer Science v. 3228, Springer Verlag.
  7. A. D. Lattner , J. D. Gehrke , I. J. Timm , O. Herzog (2005) A knowledge-based approach to behavior decision in intelligent vehicles, Intelligent Vehicles Symposium, IEEE, pp. 466-471.
  8. M. Malekovic and M. Schatten (2008) Leadership in Team Based Knowledge Management - An Autopoietic Information System's Perspective, Central European Conference on Information and Intelligent Systems (CECIIS-2008), University of Zagreb.
  9. T. Orehovacki, M. Schatten, A. Lovrencic (2011) Implementing a Logic System for Testing Functional Independent Normal Form in Relational Databases, Proceedings of the 33rd International Conference on Information Technology Interfaces / Lužar-Stiffler, Vesna ; Jarec, Iva ; Bekić, Zoran (ed). - Zagreb : University Computing Centre, University of Zagreb , 2011. 167-172 ( ISBN 978-953-7138-20-2).
  10. M. Schatten (2013) Knowledge Management in Semantic Social Networks, Computational & Mathematical Organization Theory (1381-298X) 19, 4; 538-568
  11. G. Yang and M. Kifer (2000), Flora: Implementing an Efficient DOOD System Using a Tabling Logic Engine. Intl. Conference on Computational Logic, July 2000.
  12. G. Yang, Michael Kifer, and C. Zhao (2003), FLORA-2: A Rule-Based Knowledge Representation and Inference Infrastructure for the Semantic Web. Second International Conference on Ontologies, Databases and Applications of Semantics (ODBASE), Catania, Sicily, Italy, November 2003.
  13. M. Kifer (2005), Nonmonotonic reasoning in Flora-2. Int'l Conf. on Logic Programming and Nonmonotonic Reasoning. Lecture Notes in Computer Science Volume 3662, 2005, pp 1-12.
  14. G. Yang and M. Kifer (2003), Reasoning about Anonymous Resources and Meta Statements on the Semantic Web. Journal on Data Semantics. Lecture Notes in Computer Science vol. 2800, Springer, 2003.
  15. M. Kifer, G. Yang, H. Wan, C. Zhao (2013),Flora-2 User's Manual
  16. M. Schatten, M. Cubrilo, J.Seva (2008) A Semantic Wiki System Based on F-Logic, Central European Conference on Information and Intelligent Systems (CECIIS-2008), University of Zagreb.
  17. M. Schatten, M. Cubrilo, J.Seva (2009) Dynamic Queries in Semantic Wiki Systems, Central European Conference on Information and Intelligent Systems (CECIIS-2009), University of Zagreb.
  18. M. Schatten, V. Kakulapati, M. Cubrilo (2010) Reasoning about Social Semantic Web Applications using String Similarity and Frame Logic, Central European Conference on Information and Intelligent Systems (CECIIS-2010), University of Zagreb.
  19. M. Schatten (2007) Reasonable Python or how to Integrate F-Logic into an Object-Oriented Scripting Language, Intelligent Engineering Systems (INES-2007), IEEE, pp. 297-300.
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