N-Quads serializer ignores default graph #1842
Comments
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Hmm, it's somewhat related to #1804. |
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May be related to this also:
EDIT: Actually on second thought no, maybe not. |
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I guess this is a more general issue with how rdflib serializes context-aware stores. Changing the output format to @prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix ns1: <urn:x-rdflib:> .
@prefix prov: <http://www.w3.org/ns/prov#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
_:nd65e1d4bf7a34d92a06e4e619a245037b1 {
<http://greggkellogg.net/foaf#me> a foaf:Person ;
foaf:knows "http://manu.sporny.org/about#manu" ;
foaf:name "Gregg Kellogg" .
<http://manu.sporny.org/about#manu> a foaf:Person ;
foaf:knows "http://greggkellogg.net/foaf#me" ;
foaf:name "Manu Sporny" .
}
_:N427df78321f84718beec24f5f0c7e26c {
[] prov:generatedAtTime "2012-04-09"^^xsd:date .
} |
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I noticed this issue while I was working on implementing a more efficient integration of pyld as a parser into rdflib core #1836. My implementation sets the graph name to I noticed the output in the format An easy fix (I think) is to set the context to |
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To add further to this, it may be that those other serializers are adding statements from the default graph as For example: from rdflib.graph import DATASET_DEFAULT_GRAPH_ID
# Instead of this
store.add((s, p, o), None)
# Do this
store.add((s, p, o), DATASET_DEFAULT_GRAPH_ID) |
Oops, I take that back. This only works correctly for The Currently it serializes something like: Notice the |
You're not wrong, I've been addressing this in the dataset re-work, changes to nquads serializer here |
Can't we get this in without breaking changes? |
Yes. In this instance, correcting the serialization doesn't cause any breaking changes. |
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Thanks for your work @gjhiggins. I've copied your code from the nquads serializer out into a separate PR. I hope you don't mind. I need this patch to get the JSON-LD 1.1 tests to pass. Can I ask why rdflib/rdflib/plugins/serializers/nquads.py Lines 38 to 41 in 4fba0ff I had to remove it because the serialize method was outputting double the statements. |
That's cool, I don't mind at all, whatever works for you.
It's a consequence of switching over to Dataset. |
aucampia
added
core
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Hi, I just noticed when I take the multigraph example from JSON-LD standard and convert it to N-Quads, main graph is suddenly referenced by a blank label, instead of no label. My code is: from rdflib.graph import Dataset
data = """{
"@context": [
"http://schema.org/",
{"@base": "http://example.com/"}
],
"@graph": [{
"@id": "people/alice",
"gender": [
{"@value": "weiblich", "@language": "de"},
{"@value": "female", "@language": "en"}
],
"knows": {"@id": "people/bob"},
"name": "Alice"
}, {
"@id": "graphs/1",
"@graph": {
"@id": "people/alice",
"parent": {
"@id": "people/bob",
"name": "Bob"
}
}
}, {
"@id": "graphs/2",
"@graph": {
"@id": "people/bob",
"sibling": {
"name": "Mary",
"sibling": {"@id": "people/bob"}
}
}
}]
}"""
ds = Dataset()
ds.parse(data=data, format="json-ld")
print(ds.serialize(format="nquads").strip())The result looks like this for me: <http://example.com/people/bob> <http://schema.org/name> "Bob" <http://example.com/graphs/1> .
<http://example.com/people/alice> <http://schema.org/parent> <http://example.com/people/bob> <http://example.com/graphs/1> .
<http://example.com/people/alice> <http://schema.org/gender> "female"@en _:N6535627397b54eb2b076091aaccf8a98 .
<http://example.com/people/alice> <http://schema.org/name> "Alice" _:N6535627397b54eb2b076091aaccf8a98 .
<http://example.com/people/alice> <http://schema.org/gender> "weiblich"@de _:N6535627397b54eb2b076091aaccf8a98 .
<http://example.com/people/alice> <http://schema.org/knows> <http://example.com/people/bob> _:N6535627397b54eb2b076091aaccf8a98 .
<http://example.com/people/bob> <http://schema.org/sibling> _:Na4b162b6579f4d0a9aa68d2d0f65572c <http://example.com/graphs/2> .
_:Na4b162b6579f4d0a9aa68d2d0f65572c <http://schema.org/name> "Mary" <http://example.com/graphs/2> .
_:Na4b162b6579f4d0a9aa68d2d0f65572c <http://schema.org/sibling> <http://example.com/people/bob> <http://example.com/graphs/2> .However on the JSON-LD playground, the output for N-Quads conversion looks like this instead: <http://example.com/people/alice> <http://schema.org/gender> "female"@en .
<http://example.com/people/alice> <http://schema.org/gender> "weiblich"@de .
<http://example.com/people/alice> <http://schema.org/knows> <http://example.com/people/bob> .
<http://example.com/people/alice> <http://schema.org/name> "Alice" .
<http://example.com/people/alice> <http://schema.org/parent> <http://example.com/people/bob> <http://example.com/graphs/1> .
<http://example.com/people/bob> <http://schema.org/name> "Bob" <http://example.com/graphs/1> .
<http://example.com/people/bob> <http://schema.org/sibling> _:b0 <http://example.com/graphs/2> .
_:b0 <http://schema.org/name> "Mary" <http://example.com/graphs/2> .
_:b0 <http://schema.org/sibling> <http://example.com/people/bob> <http://example.com/graphs/2> .Is this issue likely to be solved soon? |
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So is there a way to avoid |
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@namedgraph In what sense is the I think there was some trick to it, where the default graph will or won't be in there depending on how you insert it into the |
It is an issue because the default graph should not have a name, as soon as it does it is no longer the default graph. |
Uhh, no? This is not standard in any way. The 4th element of a quad should be omitted for triples in the default graph:
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My bad, you're right. Actually seems like some kind of internal rdflib thing that's leaking out by accident.
Just for completeness, I don't think this is exactly true. While it does say that if there is no graphLabel, it should be in the default graph, I don't think it specifies that a default graph may not be refered to using an IRI, in case that ever got standardised. |
Not that I know of, I will be working on fixing the Dataset issue in the coming months but it is all a bit tangled. |
Kinda explicit in the wording: “The default graph does not have a name”. My understanding is that this is inherited from SPARQL: a query that does not specify a graph name is posed of the default graph --- which in consequence, cannot have a name. However, RDFLib binds an identifier to every graph (probably inherited from the extant implementations of Store) and if an identifier isn't provided, a BNode is used. In consequence, in the RDFLib implementation, a Dataset's default graph, being an RDFLib
Because the default graph doesn't have a name, that's a must - but there are some slightly-inobvious consequences. I've spent some time looking into the issues here and I do have a mostly-complete solution that I'm using to tease out some of the options. If you'll forgive me some elaboration, I'm including some example code that uses as input a slightly-changed diff --git a/test/data/sportquads.trig b/test/data/sportquads.trig
+
+<http://example.com/resource/student_30> a ont:Student ;
+ foaf:name "Dudley Moore" .And some annotated test code ... def test_dataset_serialize():
d1 = Dataset()
d1.parse(
TEST_DATA_DIR / "sportquads.trig", # Augmented with the two triples mentioned
format="trig",
publicID="" # Uncontextualised statements -> default_graph
)
assert len(d1) == 2 # uncontextualised statements (“triples”) in the default graph
# And the contexts created ...
assert sorted(list(d1.contexts())) == [
URIRef('http://example.org/graph/practise'),
URIRef('http://example.org/graph/sports'),
URIRef('http://example.org/graph/students'),
] # Note: no mention of `<urn:x-rdflib:default>` aka “the graph with no name”
# it serializes as expected ...
assert sorted(d1.serialize(format="nquads").splitlines()) == [
"",
"<http://example.com/resource/sport_100> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://example.com/ontology/Sport> <http://example.org/graph/sports> .",
'<http://example.com/resource/sport_100> <http://www.w3.org/2000/01/rdf-schema#label> "Tennis" <http://example.org/graph/sports> .',
"<http://example.com/resource/student_10> <http://example.com/ontology/practises> <http://example.com/resource/sport_100> <http://example.org/graph/practise> .",
"<http://example.com/resource/student_10> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://example.com/ontology/Student> <http://example.org/graph/students> .",
'<http://example.com/resource/student_10> <http://xmlns.com/foaf/0.1/name> "Venus Williams" <http://example.org/graph/students> .',
"<http://example.com/resource/student_20> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://example.com/ontology/Student> <http://example.org/graph/students> .",
'<http://example.com/resource/student_20> <http://xmlns.com/foaf/0.1/name> "Demi Moore" <http://example.org/graph/students> .',
"<http://example.com/resource/student_30> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://example.com/ontology/Student> .",
'<http://example.com/resource/student_30> <http://xmlns.com/foaf/0.1/name> "Dudley Moore" .',
] # uncontextualized statements preserved as such, just as in the trig source
# Quads are no issue so let's work with uncontextualized statements
sportstriples = d1.serialize(format='nt') # Decontextualize the statements
# Use nquads parser to read triples into the default graph
d2 = Dataset()
d2.parse(
data=sportstriples,
format="nquads") # Read uncontextualized statements as nquads
assert len(d2) == 9 # All parsed into the default graph
assert len(list(d2.contexts())) == 0 # only named graphs are contexts
# Use nquads parser to read triples into a named graph (aka “context”)
d3 = Dataset()
d3.parse(
data=sportstriples,
format="nquads",
publicID=context0 # Assert a context for the uncontextualised statements
)
assert len(d3) == 0 # No triples in default graph
assert len(d3.graph(context0)) == 9 # All statements now contextualized
assert list(d3.contexts()) == [
URIRef('urn:example:context-0')
] # Only one context, as specified
# Now back to `d1` and some fun stuff ...
assert len(d1) == 2 # the two added triples
d1.default_union = True
assert len(d1) == 9 # decontextualise all statements
d1.default_union = False
assert len(d1) == 2 # back to baseWhy is it “fun stuff” - because of It is indeed tangled, the reason why this isn't a draft PR is that I'm playing whack-a-mole with the tests 😄 |
The following script can be run as-is:
Output:
Issue
I would have expected the first statement of the output to omit the graph label as it is a statement in the default graph.
See https://www.w3.org/TR/n-quads/#simple-triples for reference.
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