Consider the following snippet
ASK WHERE { wd:Q734774 wdt:P31 wd:Q3918. }
This works fine in Wikidata. I want to use some of the path syntax in the this snippet. Specifically I want to limit the number of the times "wdt:P31" used in the path. According to the guidelines this should be the right syntax:
ASK WHERE { wd:Q734774 wdt:P31{,3} wd:Q3918. }
But it's giving me weird error messages. Any ideas?
The final version of SPARQL 1.1 Property Paths lets you do this with the following query --
ASK WHERE
{ wd:Q734774
wdt:P31? / wdt:P31? / wdt:P31?
wd:Q3918
}
For clarity, I've put the full Property Path Predicate (wdt:P31? / wdt:P31? / wdt:P31?) on a separate line between Subject (wd:Q734774) and Object (wd:Q3918). The trailing ? asks for one-or-zero instances of the wdt:P31 predicate, and the / asks for a sequence, so this full path asks for a sequence of zero-or-one-or-two-or-three instances.
Related
I just started using Jena Apache, on their introduction they explain how to write out the created model. As input I'm using a Turtle syntax file containing some data about some OWL ontologies, and I'm using the #base directive to use relative URI's on the syntax:
#base <https://valbuena.com/ontology-test/> .
And then writing my data as:
<sensor/AD590/1> a sosa:Sensor ;
rdfs:label "AD590 #1 temperatue sensor"#en ;
sosa:observes <room/1#Temperature> ;
ssn:implements <MeasureRoomTempProcedure> .
Apache Jena is able to read that #base directive and expands the relative URI to its full version, but when I write it out Jena doesn't write the #base directive and the relative URI's. The output is shown as:
<https://valbuena.com/ontology-test/sensor/AD590/1> a sosa:Sensor ;
rdfs:label "AD590 #1 temperatue sensor"#en ;
sosa:observes <https://valbuena.com/ontology-test/room/1#Temperature> ;
ssn:implements <https://valbuena.com/ontology-test/MeasureRoomTempProcedure> .
My code is the following:
Model m = ModelFactory.createOntologyModel();
String base = "https://valbuena.com/ontology-test/";
InputStream in = FileManager.get().open("src/main/files/example.ttl");
if (in == null) {
System.out.println("file error");
return;
} else {
m.read(in, null, "TURTLE");
}
m.write(System.out, "TURTLE");
There are multiple read and write commands that take as parameter the base:
On the read() I've found that if on the data file the #base isn't declared it must be done on the read command, othwerwise it can be set to null.
On the write() the base parameter is optional, it doesn't matter if I specify the base (even like null or an URI) or not, the output is always the same, the #base doesn't appear and all realtive URI's are full URI's.
I'm not sure if this is a bug or it's just not possible.
First - consider using a prefix like ":" -- this is not the same as base but makes the output nice as well.
You can configure the base with (current version of Jena):
RDFWriter.create()
.source(model)
.lang(Lang.TTL)
.base("http://base/")
.output(System.out);
It seems that the command used on the introduction tutorial of Jena RDF API is not updated and they show the reading method I showed before (FileManager) which now is replaced by RDFDataMgr. The FileManager way doesn't work with "base" directive well.
After experimenting I've found that the base directive works well with:
Model model = ModelFactory.createDefaultModel();
RDFDataMgr.read(model,"src/main/files/example.ttl");
model.write(System.out, "TURTLE", base);
or
Model model = ModelFactory.createDefaultModel();
model.read("src/main/files/example.ttl");
model.write(System.out, "TURTLE", base);
Although the model.write() command is said to be legacy on RDF output documentation (whereas model.read() is considered common on RDF input documentation, don't understand why), it is the only one I have found that allows the "base" parameter (required to put the #base directive on the output again), RDFDataMgr write methods don't include it.
Thanks to #AndyS for providing a simpler way to read the data, which led to fix the problem.
#AndyS's answer allowed me to write relative URIs to the file, but did not include the base in use for RDFXML variations. To get the xml base directive added correctly, I had to use the following
RDFDataMgr.read(graph, is, Lang.RDFXML);
Map<String, Object> properties = new HashMap<>();
properties.put("xmlbase", "http://example#");
Context cxt = new Context();
cxt.set(SysRIOT.sysRdfWriterProperties, properties);
RDFWriter.create().source(graph).format(RDFFormat.RDFXML_PLAIN).base("http://example#").context(cxt).output(os);
I've been trying (with no success so far) to filter values with a "broader equals" condition. That is, ignoring diacritics.
select * where {
?s per:surname1 ?t.
bind (fn:starts-with(str(?t),'Maria') as ?noAccent1) .
bind (fn:translate(str(?t),"áéíóú","aeiou") as ?noAccent2) .
} limit 100
To this moment, I've tried with XPath functions fn:contains, fn:compare, fn:translate, fn:starts-with, but none of them seem to be working.
Is there any other way (other than chaining replaces) to add collation into these functions or achieve the same goal?
The XPath functions you mention are not part of the SPARQL standard really, so as you found out, you can't rely on them being supported out of the box (though some vendors may provide them as an add-on).
However, GraphDB (which is based on RDF4J) allows you to create your own custom functions in SPARQL. It is a matter of writing a Java class that implements the org.eclipse.rdf4j.query.algebra.evaluation.function.Function interface, and registering it in the RDF4J engine by packaging it as a Java Service Provider Interface (SPI) implementation.
SPARQL and REGEX do not support efficiently transliterating character maps. If you want an efficient implementation you would need a custom RDF4J custom as described by Jeen.
If you want a quick and dirty solution use this code sample:
PREFIX fn: <http://www.w3.org/2005/xpath-functions#>
PREFIX spif: <http://spinrdf.org/spif#>
select * where {
BIND("Mariana" as ?t) .
BIND("Márénísótú" as ?t2) .
BIND (regex(str(?t),'^Maria') as ?noAccent1) .
BIND (spif:replaceAll(
spif:replaceAll(
spif:replaceAll(
spif:replaceAll(
spif:replaceAll(str(?t2),"á","a"),
"é","e")
,"í","i"),
"ó","o"),
"ú","u") as ?noAccent2) .
}
I am trying to teach myself this weekend how to run API queries against a data source in this case data.gov. At first I thought I'd use a simple SQL variant, but it seems in this case I have to use SPARQL.
I've read through the documentation, downloaded Twinkle, and can't seem to quite get it to run. Here is an example of a query I'm running. I'm basically trying to find all gas stations that are null around Denver, CO.
PREFIX station: https://api.data.gov/nrel/alt-fuel-stations/v1/nearest.json?api_key=???location=Denver+CO
SELECT *
WHERE
{ ?x station:network ?network like "null"
}
Any help would be very much appreciated.
SPARQL is a graph pattern language for RDF triples. A query consists of a set of "basic graph patterns" described by triple patterns of the form <subject>, <predicate>, <object>. RDF defines the subject and predicate with URI's and the object is either a URI (object property) or literal (datatype or language-tagged property). Each triple pattern in a query must therefore have three entities.
Since we don't have any examples of your data, I'll provide a way to explore the data a bit. Let's assume your prefix is correctly defined, which I doubt - it will not be the REST API URL, but the URI of the entity itself. Then you can try the following:
PREFIX station: <http://api.data.gov/nrel...>
SELECT *
WHERE
{ ?s station:network ?network .
}
...setting the PREFIX to correctly represent the namespace for network. Then look at the binding for ?network and find out how they represent null. Let's say it is a string as you show. Then the query would look like:
PREFIX station: <http://api.data.gov/nrel...>
SELECT ?s
WHERE
{ ?s station:network "null" .
}
There is no like in SPARQL, but you could use a FILTER clause using regex or other string matching features of SPARQL.
And please, please, please google "SPARQL" and "RDF". There is lots of information about SPARQL, and the W3C's SPARQL 1.1 Query Language Recommendation is a comprehensive source with many good examples.
I use this sparql query to get as much cities as possible:
select * where {
?city rdf:type dbo:PopulatedPlace
}
However, some expected ones are missing e.g.
http://dbpedia.org/resource/Heidelberg
(neither that nor one of its wikiRedirects)
which is of a dbo:PopulatedPlace as this query returns true (in JSON):
ask {
:Heidelberg a dbo:PopulatedPlace
}
I need that list to be exhaustiv because later I will add constraints based on user input.
I use http://dbpedia.org/snorql/ to test the queries.
Any help is appreciated.
UPDATE:
One of the Devs told me the public endpoint is limited ( about 1K ).
I'll come up with a paginated solution and see if it contains the 'outlier'.
UPDATE2:
The outlier is definitly in the resultset of rdf:type dbo:Town.
Using dbo:PopulatedPlace yields too many results to check per hand, though.
The public endpoint limits results to about 1K. Pagination or use of a smaller subclass of dbo:PopulatedPlace yields the result.
I run a Virtuoso Server and missed a number of results when making a SPARQL-Select request. I tracked it down and find a really strange behaviour, that I cannot explain.
But to start from the beginning.
The endpoint I query can be found at http://creativeartefact.org/sparql
I) Check for a specific triple:
ASK WHERE {
<http://creativeartefact.org/mbrainzImport/f18e677a-4051-486a-aa64-d9a3bfef90af>
<http://creativeartefact.org/ontology/represents>
<http://creativeartefact.org/mbrainzImport/35ed9f2a-6ce4-44ca-9c7a-967377b0e007>. }
The query returns TRUE
II) Now getting a bit more unspecific:
ASK WHERE {
?s
<http://creativeartefact.org/ontology/represents>
<http://creativeartefact.org/mbrainzImport/35ed9f2a-6ce4-44ca-9c7a-967377b0e007>. }
If the first returns true, the second shall do as well, shouldn't it? But it doesn't. It return FALSE!
If I replace the predicate or the object with a variable, it returns true as expected. Only when setting a variable for the subject, it returns false.
That the data really exists in the triple store can be tested by running the query
SELECT * WHERE {
?s
?p
<http://creativeartefact.org/mbrainzImport/35ed9f2a-6ce4-44ca-9c7a-967377b0e007>. }
You will see, that both results comw with p = http://creativeartefact.org/ontology/represents - which is exactly the predicate I am asking for in the former query.
To make it even more strange, there ARE triples with the aforementioned format, that return the triples:
select * {
?s
<http://creativeartefact.org/ontology/represents>
<http://creativeartefact.org/mbrainzImport/e4003568-5645-4ee1-abd0-2e8156272e59>. }
Any idea, what is happening here?
Thanks in advance,
Frank
The Virtuoso being used is an original 07.00.3203 build from 2013.
I would suggest upgrading to the latest Virtuoso 07.10.3211, open source or commercial, depending on which is in use here, and see if the problem persists ...