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Add support for empty graphs in the subject and object positions #374

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Add support for empty graphs in the subject and object positions #374

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671ce00
fix: support empty graphs in subject and object positions for parsing…
Dexagod Dec 6, 2023
fcd0d9b
fix: empty graphs are now correctly represented as true^^xsd:boolean
Dexagod Dec 6, 2023
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19 changes: 17 additions & 2 deletions src/N3Parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -663,8 +663,23 @@ export default class N3Parser {
const graph = this._graph;

// Store the last quad of the formula
if (this._subject !== null)
this._emit(this._subject, this._predicate, this._object, graph);

if (this._subject !== null) {
// Catch the empty graph being closed when parsing N3.
// In this case, we emit the empty graph as the value "true"^^xsd:boolean
if (!this._predicate && !this._object) {
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Is it sufficient to check that there is no predicate?

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The predicate check should be sufficient, as the flow goes as follows:
at the start of the formula the this._readSubject function is called. This one sets the this._predicate value to null.
As the token here is }, the this._readPunctuation function is called, that then calls the this._readFormulaTail function.
In here, we find this code. So I concluded that we should only check on the this._predicate value being null, and not the this._object, as the predicate value alone should be enough of an indicator and I am unsure how the object gets there in all flows.

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Okay. so let's do if (this._predicate === null) indeed.

const outerGraph = this._contextStack[this._contextStack.length - 1].graph;
this._emit(
graph,
this._namedNode('http://www.w3.org/1999/02/22-rdf-syntax-ns#value'),
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Probably want to use a constant for this.

this._literal('true', this._namedNode('http://www.w3.org/2001/XMLSchema#boolean')),
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Probably want to use a constant for this.

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This was an error on my part.
I represented the empty graph as a blank node with an rdf:value of "true"^^xsd:boolean,
whereas I was corrected that it should be directly replaced with "true"^^xsd:boolean.

outerGraph
); // Restore the parent context containing this formula
}
else {
this._emit(this._subject, this._predicate, this._object, graph);
}
}

// Restore the parent context containing this formula
this._restoreContext('formula', token);
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41 changes: 40 additions & 1 deletion test/N3Parser-test.js
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Expand Up @@ -1763,7 +1763,7 @@ describe('Parser', () => {
return isImpliedBy ? [to, 'http://www.w3.org/2000/10/swap/log#isImpliedBy', from] : [from, 'http://www.w3.org/2000/10/swap/log#implies', to];
}

describe(`A Parser instance for the N3 format with rdfStar support disabled and with ${isImpliedBy ? 'enabled' : 'disabled'}`, () => {
describe(`A Parser instance for the N3 format with rdfStar support disabled and with isImpliedBy ${isImpliedBy ? 'enabled' : 'disabled'}`, () => {
function parser() { return new Parser({ baseIRI: BASE_IRI, format: 'N3', rdfStar: false, isImpliedBy }); }

describe('should parse a single triple',
Expand Down Expand Up @@ -2337,6 +2337,45 @@ describe('Parser', () => {
it('should not parse RDF-star in the object position',
shouldNotParse(parser, '<a> <b> <<<a> <b> <c>>>.',
'Unexpected RDF-star syntax on line 1.'));

describe('should parse the empty graph as an rdf:value of "true"^^xsd:boolean in the object position',
shouldParse(parser, '<a> <b> {}.',
['a', 'b', '_:b0'],
['_:b0', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean']
));

// describe('should parse the empty graph as an rdf:value of "true"^^xsd:boolean in the predicate position',
// shouldParse(parser, '<a> {} <c>.',
// ['a', '_:b0', 'c'],
// ['_:b0', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean']
// ));

describe('should parse the empty graph as an rdf:value of "true"^^xsd:boolean in the subject position',
shouldParse(parser, '{} <b> <c>.',
['_:b0', 'b', 'c'],
['_:b0', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean']
));

describe('should parse the empty graph in the object position as an rdf:value of "true"^^xsd:boolean while retaining the encompassing graph',
shouldParse(parser, '<a> <b> { <x> <y> {} }.',
['a', 'b', '_:b0'],
['x', 'y', '_:b1', '_:b0'],
['_:b1', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean', '_:b0']
));

// describe('should parse the empty graph in the predicate position as an rdf:value of "true"^^xsd:boolean while retaining the encompassing graph',
// shouldParse(parser, '<a> <b> { <x> {} <z> }.',
// ['a', 'b', '_:b0'],
// ['x', '_:b1', 'z', '_:b0'],
// ['_:b1', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean', '_:b0']
// ));

describe('should parse the empty graph in the subject position as an rdf:value of "true"^^xsd:boolean while retaining the encompassing graph',
shouldParse(parser, '<a> <b> { {} <y> <z> }.',
['a', 'b', '_:b0'],
['_:b1', 'y', 'z', '_:b0'],
['_:b1', 'http://www.w3.org/1999/02/22-rdf-syntax-ns#value', '"true"^^http://www.w3.org/2001/XMLSchema#boolean', '_:b0']
));
});
}

Expand Down
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