High Quality Content by WIKIPEDIA articles! The IMS Vocabulary Definition Exchange (VDEX) specification is a grammar for controlled vocabularies.IMS VDEX allows the exchange and expression of simple machine-readable lists of human language terms, along with information that may assist a human in understanding the meaning of the various terms. Put more simply, it is a mark-up language or grammar for controlled vocabularies, with VDEX allowing the description and creation of controlled vocabularies that could be easily interchanged.