The National Center for Biomedical Ontology (NCBO) Bio- Portal provides common access for browsing and querying a large set of ontologies that are commonly used in biomedical communities. One of our missions is to align lexical features (i.e., textual definitions) that are commonly used in these ontologies across different representation for- mats with standard tags and to represent them in a standard way to the users. The Simple Knowledge Organization System (SKOS) is a recom- mendation of the World-Wide-Web Consortium (W3C) for a common data model for sharing and linking knowledge organization systems on the Semantic Web. The BioPortal is in the process of adopting SKOS in the backend representation for its content. During this process, we dis- covered that there exists a set of commonly-used lexical features shared by the biomedical ontologies that SKOS does not yet represent. In this paper, we discuss our proposed SKOS extensions to cover this set of com- monly used lexical features, the rationales, and the detailed description of each proposed construct.
