Keywords are typically used to qualify rows in a table. However, the fact that a keyword denotes a concept, which belongs to a specific knowledge domain, is not semantically enforced in current database systems. This paper proposes defining ontology based referential constraint for such keyword columns. A query on ontology, specified as part of the referential constraint, is used to identify the domain for the keyword column. Furthermore, since ontology may evolve causing change to the domain of the keyword column, the paper proposes use of ontology based transformation functions to either automatically evolve or to recommend refinements for the values in the keyword column. Also, queries on a keyword column can perform semantic match, that is, match a keyword to related terms based on the associated ontology. Thus, the proposed approach of semantically connecting keyword columns to ontologies 1) enhances semantic data integrity, 2) facilitates evolution of keyword columns with the referenced ontology, and 3) enables semantic match queries on keyword columns.