Here are some general readings on the foundations of concepts, concept representation, and knowledge organization. Add to the list in the comment if you would like to recommend some other similar readings.
Books:
Gärdenfors, P. (2000). Conceptual Spaces: The Geometry of Thought. The MIT Press.
Widdows, D. (2004). Geometry and meaning. CSLI Publication, Standford University.
Lamberts, K., & Shanks, D. (Eds.). (1997). Knowledge, concepts, and categories. Cambridge, MA: The MIT Press.
Soergel, D. (1985). Organizing information: Principles of data base and retrieval systems. Academic Press Professional.
Articles:
Hjorland, B. (2003). Fundamentals of Knowledge Organization. Knowledge Organization. 30(2), 87-111.
Smith, B. (2004). Beyond concepts: Ontology as reality representation. Proceedings of FOIS 2004, International Conference on Formal Ontology and Information Systems, Turin, 4-6, Nov. 2004.
Binding, C. & Tudhope, D. (2004). KOS at your service: Programmatic access to knowledge organization systems. Journal of Digital Information, 4(4), 2004. http://journals.tdl.org/jodi/article/viewArticle/110/109 (See full annotation: http://research.cis.drexel.edu/MCD/?p=36)
Soergel, D. (2006). The Architecture of Meaning A Commentary. Perspective on Cognition, A Festschrift for Manfred Wettler. Rapp et al. (2006):501-16.
