What is an RDF datatype?

What is a datatype in RDF?  

Concepts says (in Section 3.3)
	RDF uses the datatype abstraction defined by XML Schema Part 2:
	Datatypes ...

XML Schema Part 2 says
	... a datatype is a 3-tuple, consisting of a) a set of distinct
	values, called its value space, b) a set of lexical
	representations, called its lexical space, and c) a set of facets
	that characterize properties of the value space, individual values
	or lexical items.

(Actually this appears to be a bug in the XML Schema documents, as the
lexical-to-value mapping is nowhere indicated.)  Let us thus assume that as
far as RDF is concerned, this allusion makes a datatype be a value space, a
lexical space, a mapping from the latter to the former, and a set of
facets.

So what happened to the XML Schema datatype facets?  Are they part of RDF
datatypes?