How to filter by BlankNode id

Question

I'm trying to run this query in the SPARQL playground on GraphDB.

select * where { 
    ?s content:value ?value .
    FILTER REGEX(str(?value), "_:x1697BD364N0abcdd866d54")
}

?value are BNodes

I'm trying to filter all values where the BNode ID is: _:x1697BD364N0abcdd866d54

I've tried a few different ways to filter by the ID:

FILTER REGEX(str(?value), "#bnode-id")
FILTER (?value), "#bnode-id")

but none was a success.

Questions:

How would you filter based on a bnode id?
Is it possible to STR(bnode) ?

That can't work with blank nodes in SPARQL query even not with labeled blank nodes because blank nodes in graph patterns i) act as non-distinguished variables and ii) do **not** act as references to specific blank nodes in the RDF dataset. — UninformedUser, Mar 31 '19 at 13:34
The obvious solution would be to determine the blank node by some of its properties. — UninformedUser, Mar 31 '19 at 13:35
It's true. I'm still new to sparql :) so I guess my set of tools is a work in progress — ueeieiie, Apr 01 '19 at 09:27

score 4 · Answer 1 · edited Jun 20 '20 at 09:12

4

How would you filter based on a bnode id label?

See the blank-nodes tag info. In short, one can't rely on blank node labels in SPARQL queries:

There need not be any relation between a label _:a in the result set and a blank node in the data graph with the same label.

An application writer should not expect blank node labels in a query to refer to a particular blank node in the data.

If it is hard to distinguish blank nodes by their properties etc. in SPARQL, one can use GraphDB's internal resource identifiers.

PREFIX ent: <http://www.ontotext.com/owlim/entity#>
SELECT * {
    ?s content:value ?value .
    ?s ent:id ?id .
    FILTER (?id = 424242)
}

or

PREFIX ent: <http://www.ontotext.com/owlim/entity#>
SELECT * {
    ?s content:value ?value 
    BIND (ent:id(?s) AS ?id)
    FILTER (?id = 424242)
}

Is it possible to STR(bnode)?

No. From 17.4.2.5 str:

simple literal  STR (literal ltrl)
simple literal  STR (IRI rsrc)
Returns the lexical form of ltrl (a literal); returns the codepoint representation of rsrc (an IRI).

edited Jun 20 '20 at 09:12

Community

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answered Mar 31 '19 at 20:48

Stanislav Kralin

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That's nice I was looking for a way to filter by bnode id, because I was looking for a specific id which I had. The GraphDB identifier is not a number which can help me here. but anyway, thats a nice trick :) – ueeieiie Mar 31 '19 at 21:41
Do you have these blank node labels in your RDF file you want to import? These labels will change after importing. – Stanislav Kralin Mar 31 '19 at 22:04
@ueeiieu isn't it possible to identify the blank node by some of its properties? – UninformedUser Apr 01 '19 at 13:46
@AKSW It is possible. My questions was mostly theoretical. I wanted to know why can I get the Blanknode ID – ueeieiie Apr 01 '19 at 14:04

How to filter by BlankNode id

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