I have two graphs, in one the literals are tagged (#de) in the other untagged. I need a join between the two. The trivial solution with a filter runs very slow.
WHERE {
?tok nlp:lemma ?lem .
?tok2 wn:form ?t .
filter (?tok2 = ?t) .
...
An improved version which works with fuseki is
WHERE {
?tok nlp:lemma ?lem .
Bind (str(?lem) as ?lems) .
?lu :orthForm ?lems .
...
I tried ?lu :xx (str(?lem)) . but this is flagged as an error. Why?
Similarly, using value ?lems {str(?lem)}.
I assume naively that the bind does not create much overhead, thus the above solution probably o.k.
Would the same approach work for searching when the language codes are different my previous question
The only thing allowed in a triple pattern are variables, URIs, literals (in object) and bnodes. Hence instead of the pattern ?lu :xx (str(?lem)), you will need to use a BIND or projection to convert the variable to a string. Taking the first example:
WHERE {
?lu :xx ?langLem .
BIND(str(?langLem) AS ?lem)
}
Or, using projection:
SELECT (str(?langLem) AS ?lem)
WHERE {
?lu :xx ?langLem .
}
I assume you are trying to use the VALUES statement in value ?lems {str(?lem)}. VALUES is normally used to bind variables to a set of values, e.g.:
VALUES ?lem { :Euclid :Gauss }
?lem rdfs:label ?label .
...binds ?lem to :Euclid and :Gauss and executes the query, returning the union of results. I.e. it is the same as:
{ :Euclid rdfs:label ?label }
UNION
{ :Gauss rdfs:label ?label }
I want to RDFising data, I need construct with a SPARQL query (I'm using SPIN) an object (Book) with two properties (Title and Author). All books have "Title" but sometime haven't "Author".
When this happens, it doesn't create this "Book", and I want create it with "Title".
I'm using GraphDB and this is the query:
prefix spif: <http://spinrdf.org/spif#>
prefix pres: <http://example.com/pruebardf/>
CONSTRUCT {
?rdfIRI a pres:Book ;
pres:Author ?author .
}
WHERE {
SERVICE <http://localhost:7200/rdf-bridge/1683716393221> {
?bookRow a <urn:Row> ;
<urn:col:Author> ?author ;
<urn:col:Title> ?title .
}
BIND(IRI(CONCAT("http://example.com/", spif:encodeURL(?title))) AS ?rdfIRI)
}
Is there a solution? I can use other SPARQL syntax.
Use OPTIONAL in the SERVICE part to make the pattern not fail when <urn:col:Author> is missing.
The CONSTRUCT will then simply not put in the ?rdfIRI pres:Author ?author triple but will include ?rdfIRI a pres:Book.
If you want to set ?author when it is missing in the data, look at using COALESCE.
I have the following federated SPARQL query that works as I expect in TopBraid Composer Free Edition (version 5.1.4) but does not work in Apache Fuseki (version 2.3.1):
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX dcterms: <http://purl.org/dc/terms/>
SELECT ?s WHERE {
SERVICE <http://data.linkedmdb.org/sparql> {
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
SERVICE <http://dbpedia.org/sparql?timeout=30000> {
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
}
}
I monitor the sub SPARQL queries that are being executed under the hood and notice that TopBraid correctly executes the following query to the http://dbpedia.org/sparql endpoint:
SELECT *
WHERE
{ ?s ?p ?o
FILTER regex(str(?s), replace("Paul Reubens", " ", "_"))
}
while Apache Fuseki executes the following sub query:
SELECT *
WHERE
{ ?s ?p ?o
FILTER regex(str(?s), replace(?actorName, " ", "_"))
}
Notice the difference; TopBraid replace the variable ?actorName with a particular value 'Paul Reubens', while Apache Fuseki does not. This results in an error from the http://dbpedia.org/sparql endpoint because the ?actorName is used in the result set but not assigned.
Is this a bug in Apache Fuseki or a feature in TopBraid? How can I make Apache Fuseki correctly execute this Federated query.
update 1: to clarify the behaviour difference between TopBraid and Apache Fuseki a bit more. TopBraid executes the linkedmdb.org subquery first and then executes the dbpedia.org subquery for each result of the linkedmdb.org query )(and substitutes the ?actorName with the results from the linkedmdb.org query). I assumed Apache Fuseki behaves similar, but the first subquery to dbpedia.org fails (because ?actorName is used in the result set but not assigned) and so it does not continue. But now I am not sure if it actually want to execute the subquery to dbpedia.org multiple times, because it never gets there.
update 2: I think both TopBraid and Apache Fuseki use Jena/ARQ, but I noticed that in stack traces from TopBraid the package name is something like com.topbraid.jena.* which might indicate they use a modified version of Jena/ARQ?
update 3: Joshua Taylor says below: "Surely you wouldn't expect the second service block to be executed for each one of them?". Both TopBraid and Apache Fuseki use exactly this method for the following query:
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX dcterms: <http://purl.org/dc/terms/>
SELECT ?film ?label ?subject WHERE {
SERVICE <http://data.linkedmdb.org/sparql> {
?film a movie:film .
?film rdfs:label ?label .
?film owl:sameAs ?dbpediaLink
FILTER(regex(str(?dbpediaLink), "dbpedia", "i"))
}
SERVICE <http://dbpedia.org/sparql> {
?dbpediaLink dcterms:subject ?subject
}
}
LIMIT 50
but I agree that in principle they should execute both parts once and join them, but maybe for performance reasons they chose a different strategy?
Additionally, notice how the above query works on Apache Fuseki, while the first query of this post does not. So, Apache Fuseki is actually behaving similarly to TopBraid in this particular case. It seems to be related to using an URI variable (?dbpediaLink) in two triple patterns (which works in Fuseki) compared to using a String variable (?actorName) from a triple pattern in a FILTER regex function (which does not work in Fuseki).
Updated (Simpler) Response
In the original answer I wrote (below), I said that the issue was that SPARQL queries are executed innermost first. I think that that still applies here, but I think the problem can be isolated even more easily. If you have
service <ex1> { ... }
service <ex2> { ... }
then the results have to be what you'd get from executing each query separately on the endpoints and then joining the results. The join will merge any results where the common variables have the same values. E.g.,
service <ex1> { values ?a { 1 2 3 } }
service <ex2> { values ?a { 2 3 4 } }
would execute, and you'd have two possible values for ?a in the outer query (2 and 3). In your query, the second service can't produce any results. If you take:
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
and execute it at DBpedia, you shouldn't get any results, because ?actorName isn't bound, so the filter will never succeed. It appears that TopBraid is performing the first service first and then injecting the resulting values into your second service. That's convenient, but I don't think it's correct, because it returns different results than what you'd get if the DBpedia query had been executed first and the other query executed second.
Original Answer
Subqueries in SPARQL are executed inner-most first. That means that a query like
select * {
{ select ?x { ?x a :Cat } }
?x foaf:name ?name
}
Would first find all the cats, and would then find their names. "Candidate" values for ?x are determined first by the subquery, and then those values for ?x are made available to the outer query. Now, when there are two subqueries, e.g.,
select * {
{ select ?x { ?x a :Cat } }
{ select ?x ?name { ?x foaf:name ?name } }
}
the first subquery is going to find all the cats. The second subquery finds all the names of everything that has a name, and then in the outer query, the results are joined to get just the names of the cats. The values of ?x from the first subquery aren't available during the execution of the second subquery. (At least in principle, a query optimizer might be able to figure out that some things should be restricted.)
My understanding is that service blocks have the same kind of semantics. In your query, you have:
SERVICE <http://data.linkedmdb.org/sparql> {
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
SERVICE <http://dbpedia.org/sparql?timeout=30000> {
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
}
You say that tracing shows that TopBraid is executing
SELECT *
WHERE
{ ?s ?p ?o
FILTER regex(str(?s), replace("Paul Reubens", " ", "_"))
}
If TopBraid already executed the first service block and got a unique solution, then that might be an acceptable optimization, but what if, for instance, the first query had returned multiple bindings for ?actorName? Surely you wouldn't expect the second service block to be executed for each one of them? Instead, the second service block is executed as written, and will return a result set that will be joined with the result set from the first.
The reason that it probably "doesn't work" in Jena is because the second query doesn't actually bind any variables, so it's pretty much got to look at every triple in the data, which is obviously going to take a long time.
I think that you can get around this by nesting the service calls. If nested service are all launched by the "local" endpoint (i.e., nesting a service call doesn't ask a remote endpoint to make another remote query), then you might be able to do:
SERVICE <http://dbpedia.org/sparql?timeout=30000> {
SERVICE <http://data.linkedmdb.org/sparql> {
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
}
That might get you the kind of optimization that you want, but that still seems like it might not work unless DBpedia has some efficient ways of figuring out which triples to retrieve based on computing the replace. You're asking DBpedia to look at all its triples, and then to keep the ones where the string form of the subject matches a particular regular expression. It'd probably be better to construct that IRI manually in a subquery and then search for it. I.e.,
SERVICE <http://dbpedia.org/sparql?timeout=30000> {
{ select ?actor {
SERVICE <http://data.linkedmdb.org/sparql> {
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
bind(iri(concat("http://dbpedia.org/resource",
replace(?actorName," ","_")))
as ?actor)
} }
?actor ?p ?o
}
(long comment)
Consider:
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX dcterms: <http://purl.org/dc/terms/>
SELECT ?s WHERE {
{
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
{
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
}
}
that is the same query but with no SERVICE calls.
?actorName is not in a pattern of the inner second {}.
As join is a commutative operation, this has the same answers as the first query.
SELECT ?s WHERE {
{
?s ?p ?o .
FILTER(regex(str(?s), replace(?actorName, " ", "_"))) .
}
{
<http://data.linkedmdb.org/resource/film/1> movie:actor ?actor .
?actor movie:actor_name ?actorName .
}
}
The SERVICE version highlights this because the parts are executes separately on different machines.
The join of the two parts happens on the results of each part.
I need a Sparql query to recover the Type of a specific DBpedia resource. Eg.:
pt.DBpedia resource: http://pt.dbpedia.org/resource/Argentina
Expected type: Country (as can be seen at http://pt.dbpedia.org/page/Argentina)
Using pt.DBpedia Sparql Virtuoso Interface (http://pt.dbpedia.org/sparql) I have the query below:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
select ?l ?t where {
?l rdfs:label "Argentina"#pt .
?l rdf:type ?t .
}
But it is not recovering anything, just print the variable names. The virtuoso answer.
Actually I do not need to recover the label (?l) too.
Anyone can fix it, or help me to define the correct query?
http in graph name
I'm not sure how you generated your query string, but when I copy and paste your query into the endpoint and run it, I get results, and the resulting URL looks like:
http://pt.dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fpt.dbpedia.org&sho...
However, the link in your question is:
http://pt.dbpedia.org/sparql?default-graph-uri=pt.dbpedia.org%2F&should-sponge...
If you look carefully, you'll see that the default-graph-uri parameters are different:
yours: pt.dbpedia.org%2F
mine: http%3A%2F%2Fpt.dbpedia.org
I'm not sure how you got a URL like the one you did, but it's not right; the default-graph-uri needs to be http://pt.dbpedia.org, not pt.dbpedia.org/.
The query is fine
When I run the query you've provided at the endpoint you've linked to, I get the results that I'd expect. It's worth noting that the label here is the literal "Argentina"#pt, and that what you've called ?l is the individual, not the label. The individual ?l has the label "Argentina"#pt.
We can simplify your query a bit, using ?i instead of ?l (to suggest individual):
select ?i ?type where {
?i rdfs:label "Argentina"#pt ;
a ?type .
}
When I run this at the Portuguese endpoint, I get these results:
If you don't want the individual in the results, you don't have to select it:
select ?type where {
?i rdfs:label "Argentina"#pt ;
a ?type .
}
or even:
select ?type where {
[ rdfs:label "Argentina"#pt ; a ?type ]
}
If you know the identifier of the resource, and don't need to retrieve it by using its label, you can even just do:
select ?type where {
dbpedia-pt:Argentina a ?type
}
type
==========================================
http://www.w3.org/2002/07/owl#Thing
http://www.opengis.net/gml/_Feature
http://dbpedia.org/ontology/Place
http://dbpedia.org/ontology/PopulatedPlace
http://dbpedia.org/ontology/Country
http://schema.org/Place
http://schema.org/Country
I'm working with the following SPARQL query, which is an example on the web-based end of my institution's SPARQL endpoint;
SELECT ?building_number ?name ?occupants WHERE {
?site a org:Site ;
rdfs:label "Highfield Campus" .
?building spacerel:within ?site ;
skos:notation ?building_number ;
rdfs:label ?name .
OPTIONAL {
?building soton:buildingOccupants ?occ .
?occ rdfs:label ?occupants .
} .
} ORDER BY ?name
The problem is that as well as getting data from 'Buildings and Places', the Dataset I'm interested in, and would expect the example to use, it also gets data from the 'Facilities and Equipment' dataset, which isn't relevant. You should see this if you follow the link.
I suspect the example may pre-date the addition of the Facilities and Equipment dataset, but even with the research I've done into SPARQL, I can't see a clear way to define which datasets to include.
Can anyone recommend a starting point to limit it to just show 'Buildings', or, more specifically, results from the 'Buildings and Places' dataset.
Thanks
First things first, you really need to use SELECT DISTINCT, as otherwise you'll get repeated results.
To answer your question, you can use GRAPH { ... } to filter certain parts of a SPARQL query to only match data from a specific dataset. This only works if the SPARQL endpoint is divided up into GRAPHs (this one is). The solution you asked for isn't the best choice, as it assumes that things within sites in the 'places' dataset will always be resticted to buildings... That's risky -- as it might end up containing trees and signposts at some time in the future.
Step one is to just find out what graphs are in play:
SELECT DISTINCT ?g1 ?building_number ?name ?occupants WHERE {
?site a org:Site ;
rdfs:label "Highfield Campus" .
GRAPH ?g1 { ?building spacerel:within ?site ;
skos:notation ?building_number ;
rdfs:label ?name .
}
OPTIONAL {
?building soton:buildingOccupants ?occ .
?occ rdfs:label ?occupants .
} .
} ORDER BY ?name
Try it here: http://is.gd/WdRAGX
From this you can see that http://id.southampton.ac.uk/dataset/places/latest and http://id.southampton.ac.uk/dataset/places/facilities are the two relevant ones.
To only look for things 'within' a site according to the "places" graph, use:
SELECT DISTINCT ?building_number ?name ?occupants WHERE {
?site a org:Site ;
rdfs:label "Highfield Campus" .
GRAPH <http://id.southampton.ac.uk/dataset/places/latest> {
?building spacerel:within ?site ;
skos:notation ?building_number ;
rdfs:label ?name .
}
OPTIONAL {
?building soton:buildingOccupants ?occ .
?occ rdfs:label ?occupants .
} .
} ORDER BY ?name
Alternate solutions:
Using rdf:type
Above I've answered your question, but it's not the answer to your problem. This solution is more semantic as it actually says 'only give me buildings within the campus' which is what you really mean.
Instead of filtering by graph, which is not very 'semantic' you could also restrict ?building to be of class 'building' which research facilities are not. They are still sometimes listed as 'within' a site. Usually when the uni has only published what campus they are on but not which building.
?building a rooms:Building
Using FILTER
In extreme cases you may not have data in different GRAPHS and there may not be an elegant relationship to use to filter your results. In this case you can use a FILTER and turn the building URI into a string and use a regular expression to match acceptable ones:
FILTER regex(str(?building), "^http://id.southampton.ac.uk/building/")
This is bar far the worst option and don't use it if you have to.
Belt and Braces
You can use any of these restictions together and a combination of restricting the GRAPH plus ensuring that all ?buildings really are buildings would be my recommended solution.