XAML, SOAP 1.2 Part II Section 3, and RDF "All three support the notion of named properties...the notion of sequences of values...[and] the notion of atomic values."
"...RDF expects you to buy into a URI-based resource model and only added the notion of "blank nodes" recently. For data transfer applications (which are exceedingly common), there often isn't a persistent URI or ID for the data being represented. Query results that use projection are a great example where having to cons up URI is overkill.
On the upside, RDF is unique amongst the three in its ability to have properties on properties on properties on…. Being able to treat an RDF statement as a resource that itself can have properties (in addition to the object or "value" of the property) is certainly powerful and appeals to the inner modeling geek."
I think the notion of blank nodes has been around since at least 1999.