The Shapes Constraint Language, or Shacl, provides a vocabulary for defining constraints on R·D·F graphs. In this sense, it is very useful as a base model for describing how vocabularies should be used, but not very useful for modelling concepts within the vocabularies themselves. Consequently, most terms from Shacl are not defined here. However, this ontology does annotate itself with , to declare which prefixes it recommends and uses for various name·spaces.