"Typically a value vocabulary define concepts related to described resources (persons, languages, countries, etc.).
They are "building blocks" with which metadata records can be populated.
local value vocabularies (SKOS) - defined for the local needs of digital resources' description
A value vocabulary thus represents a controlled list of allowed values for an element.
To be useful for linking of data, value vocabularies should have HTTP URIs assigned for each value;
these URIs would then appear in a metadata record instead of or in addition to the literal value."
W3C Library Linked Data Incubator Group