Abstract. Provided are the formal text descriptions of the problem-oriented XML/RDF languages, which are the basic Semantic Web languages. The availability of such descriptions guarantees the ability to implement the XML/RDF languages with the implementation of the interpreter of the NFK metalanguage. It is shown that the expressiveness of the NFK metalanguage in describing the syntax of the given pair of languages is quite comparable with EBNF expressiveness.

Keywords: Normal Forms of Knowledge Metalanguage, formal description of Metalanguage, eXtensible Markup Language, Resource Description Framework, Semantic Web.