Blank-nodes collisions

[nleguillarme]

Hi.

If I understand correctly the graphs merging process explained here, the following piece of code should create a graph with two distinct blank nodes :

from rdflib import Graph

graph1 = """
_:0 <http://purl.obolibrary.org/obo/RO_0002350> <http://www.gbif.org/species/0000001> .
"""
graph2 = """
_:0 <http://purl.obolibrary.org/obo/RO_0002350> <http://www.gbif.org/species/0000002> .
"""

g = Graph()
g.parse(data=graph1, format="nt")
g.parse(data=graph2, format="nt")

for triple in g:
    print(triple)

However, when executing the code, I get the following output :

(rdflib.term.BNode('Ne3fd8261b37741fca22d502483d88964'), rdflib.term.URIRef('http://purl.obolibrary.org/obo/RO_0002350'), rdflib.term.URIRef('http://www.gbif.org/species/0000002')) (rdflib.term.BNode('Ne3fd8261b37741fca22d502483d88964'), rdflib.term.URIRef('http://purl.obolibrary.org/obo/RO_0002350'), rdflib.term.URIRef('http://www.gbif.org/species/0000001'))

Am I missing something ? (versions : rdflib 4.2.2, python 3.7.5)

[white-gecko]

I think you understand it correctly. I think this is related to issue #892 . The rdflib uses the blank identifiers as they are.

Changing this behavior now would break some things and as we are in the feature freeze for 5.x I moved it to the 6.0.0 milestone.

Actually I have a use case where I need to parse multiple files within the same context of blank identifiers. When executing SPARQL queries I need to have individual contexts per query. Maybe it would be a good idea to introduce some blank context object which can be handed over to the parse method and the query method. We have to put this on the roadmap for 6.0.0.

[nleguillarme]

Thank you for your reply. However I don't really understand... does that mean that there is no graph merging mechanism currently implemented in rdflib ? This would be in contradiction with what is said in the doc :

In RDFLib, blank nodes are given unique IDs when parsing, so graph merging can be done by simply reading several files into the same graph

https://rdflib.readthedocs.io/en/stable/merging.html

[sanyam19106]

but both the graph have common subject and predicate and object is different.

[vikash18086]

we solve this issue as follows,
We take the new map through which we were assigning new ids to each new blank nodes of different graphs. If two blank nodes came from the same graph then we assign the same id.
you can download the updated code from the URL #1101

[white-gecko]

@vikash18086 thank you for contributing to the RDFlib. I think this would not actually solve the issue. As I have mentioned earlier:

Actually I have a use case where I need to parse multiple files within the same context of blank identifiers. When executing SPARQL queries I need to have individual contexts per query. Maybe it would be a good idea to introduce some blank context object which can be handed over to the parse method and the query method. We have to put this on the roadmap for 6.0.0.

So we need some way to:

1. reference blank nodes across graphs within a dataset/conjunctive graph
2. allow to parse multiple documents within the same context of blank nodes
3. allow to parse files in different contexts