descriptive metadata specification
Let = be a set of literals defined as the union ofdomains of simple datatypes (e.g., strings, numbers, dates, etc.). Let also and represent sets of labels for resources and properties respectively. A descriptive metadata specification is a structure (, , ), where:(1) : ) can assign general labels and literals from to nodes of the graph structure;(2) for each directed edge = ( , ) of , () , ( ) and ;(3) if and only if node vk has outdegree 0.