Relational data represent relationships between entities anywhere on the web (e.g. online social networks) or in the physical world (e.g. structure of the protein).
O. Corby, R. Dieng, and C. Hébert. Conceptual Structures: Logical, Linguistic, and Computational
Issues, 8th International Conference on Conceptual Structures,
ICCS 2000, Darmstadt, Germany, August 14-18, 2000, Proceedings, volume 1867 of LNCS, page 468--482. Springer, (2000)