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1. [Natural Language] A group, set, or kind sharing common attributes term (Merriam-Webster's Collegiate Dictionary. (
2 [Knowledge Representation] A collection of individuals or objects. (Diego Calvanese; Giuseppe De Giacomo; Maurizio Lenzerini (2002). Description Logics: Foundations for Class-based Knowledge Representation)
2. [BFO2.0] A maximal collection of particulars falling under a given general term; also called the extension of the term (or of the universal that the term denotes), (Arp et al., 2015 ])
4. [BioMedical ontology research and development] - A CLASS is a collection of all and only the particulars to which a given general term applies. Where the general term in question refers to a universal, then the corresponding class, called the EXTENSION of the universal (at a given time), comprehends all and only those particulars which as a matter of fact instantiate the corresponding universal (at that time). The totality of classes is wider than the totality of extensions of universals since it includes also DefinedClasses, designated by terms like ‘employee of Swedish bank’, ‘daughter of Finnish spy’ (Source: Smith, B., Kusnierczyk, W., Schober, D., & Ceusters, W. (2006). Towards a Reference Terminology for Ontology Research and Development in the Biomedical Domain. O. Bodenreider (Ed.), Proceedings of the Second International Workshop on Formal Biomedical Knowledge Representation: "Biomedical Ontology in Action" (KR-MED 2006), Baltimore, USA (pp. 57-65). Aachen: CEUR-WS.)
5. [Object Oriented Programming} An extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods) (Source: Wikipedia - Class (computer programming)).
6 [Set Theory] A collection of sets (or sometimes other mathematical objects) that can be unambiguously defined by a property that all its members share. (


  • "class" has a clear meaning in the context of XML; but its meaning is clearly defined in the context of the BFO and the OBO Foundry. I don't think we'd want to tell people to only use "class" in one of those two ways, but we could explain the difference across contexts."