How to construct graph object

[Spothedog1]

Repost from rml-core

Say I have the following CSV:

id, title, geometry
1, 'feature 1', 'POLYGON(...)'
2, 'feature 2', 'POLYGON(...)'

I'm trying to turn this into a geosparql compatible graph. Each row in the CSV would have to look like:

ex:1
    a geo:Feature ;
    skos:prefLabel "feature 1" ;
    geo:hasGeometry [
        geo:asWKT "POLYGON(...)"^^geo:wktLiteral ;
    ] ;

The graph would look like

graph LR
    A((eg:1)) -->|rdf:type| B((geo:Feature))
    A -->|skos:prefLabel| C(("feature 1"))
    A -->|geo:hasGeometry| D((BlankNode))
    D -->|geo:asWKT| E(("POLYGON (...)"))

Loading

I'm stuck on how I would generate a blank node that points to the WKT

@prefix rr: <http://www.w3.org/ns/r2rml#> .
@prefix over: <http://overturemaps.org#> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix geo: <http://www.opengis.net/ont/geosparql#> .
@prefix ex: <http://example.org/#> .

<feature> a rml:TriplesMap;

    rml:logicalSource [
        a rml:LogicalSource;
        rr:sqlVersion rr:SQL2008;
    ];

    rml:subjectMap [
        rml:template "http://example.org/#{id}" ;
        rml:class geo:Feature;
    ];

    rml:predicateObjectMap [
        rml:predicate skos:prefLabel ;
        rml:objectMap [ rml:reference "title" ]
    ];

    rr:predicateObjectMap [
        rr:predicate geo:hasGeometry;
        rr:objectMap [
#.           TODO: How would this work?
#            rr:parentTriplesMap <#GeometryMap>
          rml:termType: rml:BlankNode
        ]
    ]
.

How would I generate the triple?

<blank_node from objectMap> geo:asWKT "POLYGON(...)"^^geo:wktLiteral ;

[dachafra]

Hi @Spothedog1
At this moment, RML does not allow BN without reference to the data. To solve this issue you will need to create a new TriplesMap and make a join between both

@prefix rr: <http://www.w3.org/ns/r2rml#> .
@prefix over: <http://overturemaps.org#> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix geo: <http://www.opengis.net/ont/geosparql#> .
@prefix ex: <http://example.org/#> .

<feature> a rml:TriplesMap;

    rml:logicalSource [
        a rml:LogicalSource;
        rr:sqlVersion rr:SQL2008;
    ];

    rml:subjectMap [
        rml:template "http://example.org/#{id}" ;
        rml:class geo:Feature;
    ];

    rml:predicateObjectMap [
        rml:predicate skos:prefLabel ;
        rml:objectMap [ rml:reference "title" ]
    ];

    rr:predicateObjectMap [
        rr:predicate geo:hasGeometry;
        rr:objectMap [
            rr:parentTriplesMap <feature2>;
            rr:joinCondition [
                rr:child "id";
                rr:parent "id"
            ];
        ]
    ]
.

<feature2> a rml:TriplesMap;

    rml:logicalSource [
        a rml:LogicalSource;
        rr:sqlVersion rr:SQL2008;
    ];

    rml:subjectMap [
        rml:template "{id}" ;
        rr:termType rr:BlankNode;
    ];

[Spothedog1]

Thanks for the quick respond. In the second triplesMap,

<feature2> a rml:TriplesMap;
    rml:logicalSource [
        a rml:LogicalSource;
        rr:sqlVersion rr:SQL2008;
    ];

    rml:subjectMap [
        rml:reference "id" ;
        rr:termType rr:BlankNode;
    ];

    rml:predicateObjectMap [
        rml:predicate geo:asWKT ;
        rml:objectMap [ rml:reference "geometry" ]
        rml:datatype: geo:wktLiteral
    ];

1. Would an rml:reference work instead of an rml:template?
2. Is this proper usage of rml:datatype?

[dachafra]

Thanks for the quick respond. In the second triplesMap,

<feature2> a rml:TriplesMap;
    rml:logicalSource [
        a rml:LogicalSource;
        rr:sqlVersion rr:SQL2008;
    ];

    rml:subjectMap [
        rml:reference "id" ;
        rr:termType rr:BlankNode;
    ];

    rml:predicateObjectMap [
        rml:predicate geo:asWKT ;
        rml:objectMap [ rml:reference "geometry" ]
        rml:datatype: geo:wktLiteral
    ];

1. Would an rml:reference work instead of an rml:template?
2. Is this proper usage of rml:datatype?

1. I don't think so following the current test-cases: https://rml.io/test-cases/#rmltc0001b-csv
2. Yes (without the colon after rml:datatype). But some engines still do not use rml prefix, so maybe you need to use rr:datatype