Perform X3D Ontology query X3dSanCarlosCathedralAltarQuery_03.rq using examples/Altar.ttl to produce output file X3dSanCarlosCathedralAltarQuery_03.rq.txt:
===========================
PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl:  <http://www.w3.org/2002/07/owl#>
PREFIX xsd:  <http://www.w3.org/2001/XMLSchema#>
PREFIX x3d:  <https://www.web3d.org/specifications/x3d-4.0.xsd#>
PREFIX x3do: <https://www.web3d.org/specifications/X3dOntology4.0#>

# X3dSanCarlosCathedralAltarQuery_03.rq    Query Altar.ttl to determine Background skyColor values.

###############################################

# Every X3D knowledge base can be subject to semantic queries.

# The following query retrieves the Background skyColor used in the scene.
# The result is the following list of RGB values: (0.7216 0.8 0.9922) (cf. Listing 3, line 6).

# Note special handling of RDF lists:
# Bob DuCharme's weblog, 21 April 2014, "RDF lists and SPARQL"
# http://www.snee.com/bobdc.blog/2014/04/rdf-lists-and-sparql.html

SELECT ?backgroundNode ?skyColorListValues

WHERE
{
    ?background rdf:type                          x3do:Background ;
                x3do:skyColor/rdf:rest*/rdf:first ?skyColorListValues .

    BIND (strafter(xsd:string(?background),"#") AS ?backgroundNode)

    # TODO re-aggregate skyColor list values into list of tuples
}

###############################################
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| backgroundNode   | skyColorListValues |
=========================================
| "Background_2_2" | 0.7216             |
| "Background_2_2" | 0.8                |
| "Background_2_2" | 0.9922             |
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