IRI and BlankNode functions in datalog

[mmsge]

Is your feature request related to a problem? Please describe.
I often want to do specific rules if something is an IRI or a BlankNode. And often I also want to create these resources on the fly. Particularly I would like to be able to create IRIs to name graphs for various record keeping.

Describe the solution you'd like
I would like to work more directly with IRIs and BlankNodes in datalog. I would like to:

• Check whether a variable is a valid IRI
• Check whether a variable is a BlankNode
• Create new IRIs in the datalog based on available data
• Create BlankNodes, preferably via Skolem, based on available data