I'm trying to retrieve results from the BNCF at this endpoint .
My query (with "ab" as example) is:
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
SELECT DISTINCT ?source ?label ?content
WHERE {
?source a skos:Concept;
skos:prefLabel ?label;
skos:scopeNote ?content.
FILTER regex(str(?label), "ab", "i")
}
The query is correct in fact if you try to run it works. But when I try to get the results from my python this is the error:
SyntaxError: JSON Parse error: Unexpected EOF
This is my python code:
__3store = "http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query"
sparql = SPARQLUpdateStore(queryEndpoint=__3store)
sparql.setReturnFormat(JSON)
results = sparql.query(query_rdf).convert()
print json.dumps(result, separators=(',',':'))
I tried the code above according to this answer , before my code was like this:
__3store = "http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query"
sparql = SPARQLWrapper(__3store,returnFormat="json")
sparql.setQuery(query_rdf)
result = sparql.query().convert()
print json.dumps(result, separators=(',',':'))
but both throw the same error.
Does anyone know how to fix it? Thanks
EDIT:
This is python code, hope it is enough to understand
import sys
sys.path.append ('cgi/lib')
import rdflib
from rdflib.plugins.stores.sparqlstore import SPARQLUpdateStore, SPARQLStore
import json
from SPARQLWrapper import SPARQLWrapper, JSON
#MAIN
print "Content-type: application/json"
print
prefix_SKOS = "prefix skos: <http://www.w3.org/2004/02/skos/core#>"
crlf = "\n"
query_rdf = ""
query_rdf += prefix_SKOS + crlf
query_rdf += '''
SELECT DISTINCT ?source ?title ?content
WHERE {
?source a skos:Concept;
skos:prefLabel ?title;
skos:scopeNote ?content.
FILTER regex(str(?title), "ab", "i")
}
'''
__3store = "http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query"
sparql = SPARQLWrapper(__3store,returnFormat="json")
sparql.setQuery(query_rdf)
result = sparql.query().convert()
print result
Running this in Python shell returns:
Content-type: application/json
Warning (from warnings module):
File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/SPARQLWrapper-1.6.4-py2.7.egg/SPARQLWrapper/Wrapper.py", line 689
RuntimeWarning: Format requested was JSON, but XML (application/sparql-results+xml;charset=UTF-8) has been returned by the endpoint
<xml.dom.minidom.Document instance at 0x105add710>
So I think the result is always an XML also if I specificied Json as a return format.
There are a couple of problems playing together here:
First, you should only use SPARQLUpdateStore
from rdflib if you want to access a SPARQL store via rdflib's Graph interface (eg, you can add triples, you can iterate over them, etc.). If you want to write a SPARQL query yourself you should use SPARQLWrapper
.
Second, if you ask SPARQLWrapper to return JSON, what it does is actually ask the server for a couple of mime types that are most common and standardized for what we just call "json", as shown here and here :
_SPARQL_JSON = ["application/sparql-results+json", "text/javascript", "application/json"]
It seems as if your sever does understand application/sparql-results+json
, but not a combined "give me any of these mime-types header" as rdflib compiles it for maximum interoperability (so your server essentially doesn't fully support HTTP Accept Headers ):
curl -i -G -H 'Accept: application/sparql-results+json' --data-urlencode 'query=PREFIX skos:
<http://www.w3.org/2004/02/skos/core#>
SELECT DISTINCT ?source ?label ?content
WHERE {
?source a skos:Concept;
skos:prefLabel ?label;
skos:scopeNote ?content.
FILTER regex(str(?label), "ab", "i")
}' http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query
will return:
HTTP/1.1 200 OK
Date: Mon, 18 May 2015 13:13:45 GMT
Server: Apache/2.2.17 (Unix) PHP/5.3.6 mod_jk/1.2.31
...
Content-Type: application/sparql-results+json;charset=UTF-8
{
"head" : {
"vars" : [ ],
"vars" : [ "source", "label", "content" ],
"link" : [ "info" ]
},
"results" : {
"bindings" : [ {
"content" : {
"type" : "literal",
"value" : "Il lasciare ingiustificatamente qualcuno o qualcosa di cui si è responsabili"
},
"source" : {
"type" : "uri",
"value" : "http://purl.org/bncf/tid/12445"
},
"label" : {
"xml:lang" : "it",
"type" : "literal",
"value" : "Abbandono"
}
},
...
so everything is ok, but if we ask for the combined, more interoperable mime types:
curl -i -G -H 'Accept: application/sparql-results+json,text/javascript,application/json' --data-urlencode 'query=PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
SELECT DISTINCT ?source ?label ?content
WHERE {
?source a skos:Concept;
skos:prefLabel ?label;
skos:scopeNote ?content.
FILTER regex(str(?label), "ab", "i")
}' http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query
we get an xml result:
HTTP/1.1 200 OK
Server: Apache/2.2.17 (Unix) PHP/5.3.6 mod_jk/1.2.31
...
Content-Type: application/sparql-results+xml;charset=UTF-8
<?xml version='1.0' encoding='UTF-8'?>
...
So long story short: it's a bug in the server you're using. The following is a nasty workaround (it seems SPARQLWrapper doesn't just allow us to manually set the headers, but unconditionally overrides them in _createRequest
), but it works:
In [1]: import SPARQLWrapper as sw
In [2]: sparql = sw.SPARQLWrapper("http://digitale.bncf.firenze.sbn.it/openrdf-workbench/repositories/NS_03_2014/query")
In [3]: sparql.setReturnFormat(sw.JSON)
In [4]: sparql.setQuery(''' PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
SELECT DISTINCT ?source ?label ?content
WHERE {
?source a skos:Concept;
skos:prefLabel ?label;
skos:scopeNote ?content.
FILTER regex(str(?label), "ab", "i")
}
''')
In [5]: request = sparql._createRequest()
In [6]: request.add_header('Accept', 'application/sparql-results+json')
In [7]: from urllib2 import urlopen
In [8]: response = urlopen(request)
In [9]: res = sw.Wrapper.QueryResult((response, sparql.returnFormat))
In [10]: result = res.convert()
In [11]: result
Out[11]:
{u'head': {u'link': [u'info'], u'vars': [u'source', u'label', u'content']},
u'results': {u'bindings': [{u'content': {u'type': u'literal',
u'value': u'Il lasciare ingiustificatamente qualcuno o qualcosa di cui si \xe8 responsabili'},
u'label': {u'type': u'literal',
u'value': u'Abbandono',
u'xml:lang': u'it'},
u'source': {u'type': u'uri', u'value': u'http://purl.org/bncf/tid/12445'}},
...
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