A fundamental facet is an abstract property that characterizes a value space.
Keep in mind that this is a facet of the value space and not the lexical space
These facets are:
equal - every value space has the notion of equality.
ordered - a value space may have no order, partial order, or total order
bounded - has upper and lower bounds.
cardinality - finite or countable infinity (XML Schema is missing uncountable)
numeric - a boolean indicating whether it represents a quantity or mathematical number system