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There is no notion of order in RDF mappings, and this has implications for the RDF output #135

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bjdmeest opened this issue Jul 3, 2024 · 2 comments
Open

There is no notion of order in RDF mappings, and this has implications for the RDF output #135

bjdmeest opened this issue Jul 3, 2024 · 2 comments
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bjdmeest commented Jul 3, 2024

raised by @chrdebru

eg when 2 triplesmaps write to the same collection, it might be needed to specify the order of execution
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bjdmeest commented Jul 3, 2024

Christophe will make a good example

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chrdebru commented Jul 3, 2024

The title is misleading: it should be "There is no notion of order in RDF mappings, and this has implications for the RDF output."

data1.json
data2.json
mapping.ttl.txt
mapping-rev.ttl.txt

The mapping file has an extension .txt because I cannot upload .ttl files.

We can not rely on the order in which triples maps are declared in a mapping. We we can encounter situations in which the mapping yield a different result. The mapping.ttl and mapping-rev.ttl both contain the same triples maps, but they are switched around in the files. BURP relies on Apache Jena, and I presume they use hashes to store the nodes in memory. You can see that the execution of both mappings yields the same result, demonstrating we cannot rely on the order of the triples maps.

$ java -jar .\burp.jar -m mapping.ttl
SLF4J(W): No SLF4J providers were found.
SLF4J(W): Defaulting to no-operation (NOP) logger implementation
SLF4J(W): See https://www.slf4j.org/codes.html#noProviders for further details.
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_4> "2" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_3> "1" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_2> "b" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_1> "a" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Bag> .
<http://example.com/e/a> <http://example.com/ns#with> <http://example.com/c/a> .
System exiting with code: 0

$ java -jar .\burp.jar -m mapping-rev.ttl
SLF4J(W): No SLF4J providers were found.
SLF4J(W): Defaulting to no-operation (NOP) logger implementation
SLF4J(W): See https://www.slf4j.org/codes.html#noProviders for further details.
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_4> "2" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_3> "1" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_2> "b" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#_1> "a" .
<http://example.com/c/a> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/1999/02/22-rdf-syntax-ns#Bag> .
<http://example.com/e/a> <http://example.com/ns#with> <http://example.com/c/a> .
System exiting with code: 0

Change the IRI of one of the triples maps (e.g., <#TM1> into <#TMxxx>), and you get a different result ("1, 2, a, b").

There is no "increment function", but we can easily create one where you use functions to generate predicates p1, p2, p3, ... and end up with different outputs. I can look into creating one.

@dachafra dachafra changed the title Order of execution of triplesmaps has implications on the RDF output There is no notion of order in RDF mappings, and this has implications for the RDF output Jul 3, 2024
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