Although dealing with RDF data sources, we may reuse the metadata item model introduced in section "Metadata model SNAT" virtually unchanged. Again, table "Metadata items SNAT" gives us the names of the most important metadata items and describes the role of the item values during document construction. For example, @ctxt and @for-each items provide the mapping of a current context (set of RDF resources) to a new context (another set of RDF resources); and @src items map a context to the RDF nodes supplying data values. Note, however, that with RDF data sources the metadata item values cannot be XQuery expressions, as RDF nodes are not part of the XQuery data model, so that XQuery expressions cannot consume RDF nodes.