Reference
According to the "Description Set Model" of the DCMI Abstract Model [ABSTRACT-MODEL], a DC description set has the following structure:

• a description set is made up of one or more descriptions
• a description is made up of
  • zero or one described resource URI and
  • one or more statements
• a statement is made up of
  • exactly one property URI and
  • exactly one value surrogate
• a value surrogate is either a literal value surrogate or a non-literal value surrogate
  • a literal value surrogate is made up of
  • exactly one value string
• a non-literal value surrogate is made up of
  • zero or one value URIs
  • zero or one vocabulary encoding scheme URIs
  • zero or more value strings
• a value string is either a plain value string or a typed value string
  • a plain value string may be associated with a value string language
  • a typed value string is associated with a syntax encoding scheme URI
  • a non-literal value may be described by another description