I'm a little stuck on if a SPARQL query is possible for what I want to do:
I get that
?human wdt:P31 wd:Q5
would give me all items that are an instance of human.
Is there a similar way to find all items that are an instance of a place (e.g., town, city, country, river, continent, museum, building, etc.)?
The trick will likely be to find Wikidata class which is a good proxy for what you consider "place". The statement
?item wdt:P31/wdt:P279* wd:Q618123 .
will give you all the instances of "geographical objects" and its subclasses which might be a good starting point to explore.
Related
I'm doing small task on Sparql Query. I want to get the number of entities and number of instances. I have basic knowledge of Sparql and rdf. So I wrote sparql query to get the number of entities but i'm not 100% sure it's right. The endpoint i'm using is Dbpedia. Here's the query.
#Number of Entities
SELECT (count(?entity) AS ?Entities)
WHERE{ ?entity rdf:type ?type.
}
-----------
Output:
113715893
The output above me gives me big number. I'm just wondering is that the right query to get the number of entities?
Also I have to get the number of Instances. I'm not sure what 'instances' means. I assume that is the subclass or something.
Can anyone help me out with the task?
Hey the problems with the terms entity and instance is they are used often in different meanings. I assume Entity means every uri that can be an subject. While instance means every entity which is an instance of an owl:Class.
For the entities the query would be:
SELECT (count(distinct ?entity) AS ?Entities)
WHERE{ ?entity ?p ?o}
For instances i would write the following query:
select distinct count(distinct ?instance) where {?instance a ?class . ?class a owl:Class}
Maybe you mention the distinct before the variable i want to count? This is very important for you. Because to stick with your try an entity can have multiple types. For each of this types you will get an binding for the combination of entity & type variable. This at least leads to the fact that you will count the entity for each type you found in your query. So an entity with two types is counted twice. But I assume you want to count the entity only once - so you need to use the distinct keyword for the variable you want to count. This ensures that you only count different entities that are bound to this variable.
I am novice with SPARQL and DBpedia.
I would like to get knowledge of building simple SPARQL queries.
Could you please help me to build answer for such questions as:
Hometown of footballer (any one), List of Artists, List of Oscar winners (any year)
I think this question is probably too broad, but in case it's useful, it might make sense to describe how to approach this type of problem. For one of the problems, here's what I did.
List of Oscar winners (any year)
In this case, I started by visting the DBpedia entry for an Academy Award winner, Brad Pitt. There you'll see the property dcterms:subject category:Producers_who_won_the_Best_Picture_Academy_Award.
That category has property
skos:broader
category:Best_Picture_Academy_Award_winners which, in turn, has
skos:broader
category:Academy_Award_winners. So you could look for things that have a dcterms:subject value of some category that's connected by a path of skos:broader links to the Academy_Award_winners category. That will actually turn up some things that aren't persons, because those categories are categories of articles, not classes of entities, so you'll also want to filter down to those things which are Persons. That's probably going to give you a list of Academy Award winners, though it's possible that some are just in that category because they have some other relationship to the category:
select ?person where {
?person a dbpedia-owl:Person ;
dcterms:subject/skos:broader* category:Academy_Award_winners .
}
SPARQL results
I am trying to map DBPedia types to Wikipedia Categories, a simple example would be the following SPARQL query
select distinct ?cat where {
?s a dbpedia-owl:LacrossePlayer; dcterms:subject ?cat . filter(regex(?cat,'players','i') )
} limit 100
SPARQL Result
But this is highly inefficient as it has to first map the DBpedia types to DBpedia Named Entities(resources) and then extract their corresponding Wikipedia categories. I am trying to do this mapping for a lot of other DBpedia types.
Is there a direct or more efficient way to do this?
Improving the filter may help…
As an initial note, you may get some speedup if you remove or improve your filter. You can, of course, just remove it, but you could also make it more efficienct, since you're not really using any special regular expressions. Just do
filter contains(lcase(str(?cat)),'players')
to check whether the URI for ?cat contains the string players. It might even be better (I'm not sure) to grab the English rdfs:label of ?cat and check that, since you wouldn't have to do the case or string conversions.
… but there are lots of results.
But this is highly inefficient as it has to first map the DBpedia
types to DBpedia Named Entities(resources) and then extract their
corresponding Wikipedia categories. I am trying to do this mapping for
a lot of other DBpedia types. Is there a direct or more efficient way
to do this?
I'm not sure exactly what's inefficient in this. The only way that DBpedia types and categories are associated is that resources have types (via rdf:type) and have categories (via dcterms:subject). If you want to find the connections, then you'll need to find the instances of the type and the categories to which they belong. There may be some possibility that you can look into whether any particular infoboxes provide categories to articles and are used in the infobox mapping to provide DBpedia types. That's the only way to get category/DBpedia-types directly, without going through instances that I can think of, and I don't know whether the current dataset has that kind of information.
In general, since Wikipedia categories are not a type hierarchy, there will be lots of categories with which instances of any particular type are associated. For instance, we can count the number of categories associated with the types Fish and LacrossePlayer with a query like this:
select ?type (count(distinct ?category) as ?nCategories) where {
values ?type { dbpedia-owl:Fish dbpedia-owl:LacrossePlayer }
?type ^a/dcterms:subject ?category
}
group by ?type
SPARQL results
type nCategories
http://dbpedia.org/ontology/LacrossePlayer 346
http://dbpedia.org/ontology/Fish 2375
That query responds pretty quickly, and you can even get those categories pretty easily, too:
select distinct ?type ?category where {
values ?type { dbpedia-owl:Fish dbpedia-owl:LacrossePlayer }
?type ^a/dcterms:subject ?category
}
order by ?type
limit 4000
SPARQL results
When you start using types that have many more instances, though, these counts get big, and the queries take a while to return. E.g., a very common type like Place:
select ?type (count(distinct ?category) as ?nCategories) where {
values ?type { dbpedia-owl:Place }
?type ^a/dcterms:subject ?category
}
group by ?type
type nCategories
http://dbpedia.org/ontology/Place 191172
I wouldn't suggest trying to pull all that data down from the remote server. If you want to extract it, you should load the data locally.
I have a burning question concerning DBpedia. Namely, I was wondering how I could search for all the properties in DBpedia per page. The URI http://nl.dbpedia.org/property/einde concerns the property "einde". I would like to get all existing property/ pages. This does not seem too hard, but I don't know anything about SPARQL, so that's why I want to ask for some help. Perhaps there is some kind of dump of it, but I honestly don't know.
Rather than asking for pages whose URLs begin with, e.g., http://nl.dbpedia.org/property/, we can express the query by asking “for which values of ?x is there a triple ?x rdf:type rdf:Property in DBpedia?” This is a pretty simple SPARQL query to write. Because I expected that there would be lots of properties in DBPedia, I first wrote a query to count how many there are, and afterward wrote a query to actually list them.
There are 48292 things in DBpedia declared to be of rdf:type rdf:Property, as reported by this SPARQL query, run against one of DBpedia's SPARQL endpoints:
select COUNT( ?property ) where {
?property a rdf:Property
}
SPARQL Results
You can get the list by selecting ?property instead of COUNT( ?property ):
select ?property where {
?property a rdf:Property
}
SPARQL Results
I second Joshua Taylor's answer, however if you want to limit the properties to the Dutch DBpedia, you need to change the default-graph-uri query parameter to nl.dbpedia.org and set the SPARQL endpoint to nl.dbpedia.org/sparql, as in the following query. You will get a result-set of just above 8000 elements.
SELECT DISTINCT ?pred WHERE {
?pred a rdf:Property
}
ORDER BY ?pred
run query
These are the Dutch translations of the properties that have been mapped from Wikipedia so far. The full English list is also available. According to mappings.dbpedia.org, there are ~1700 properties with missing Dutch translations.
I've forgotten all I once new about DBpedia and SPARQL and find all the examples too complex and hard to understand when I Google for them.
What I wish to do is pass in two or three Wikipedia pages and get back the set of Wikipedia categories that all of the pages are members of.
This seems that it should be utterly simple in SPARQL so I would appreciate a very minimal example to get me started.
This is actually a variation of your earlier question about getting all pages belonging to two categories. The only difference is that this time, you want two/three subjects rather than objects, so you cannot use a comma-separated enumeration of values, but instead have to write out the triple pattern that you want to match.
For example, to get back all categories that both Spain and Portugal belong to, you could simply do a query like this:
SELECT ?cat
WHERE {
<http://dbpedia.org/resource/Spain> dcterms:subject ?cat .
<http://dbpedia.org/resource/Portugal> dcterms:subject ?cat .
}
what this query does is select all triple patterns that have the same value of ?cat for the dcterms:subject relation for the subjects 'Spain' and 'Portugal'. In other words, it retrieves precisely those categories that both resources are a member of.
The trick is to think in terms of a graph, or triples with connected subjects and objects. It's a bit of a mental shift but once you've got that, query writing becomes a lot easier.
The mapping between wikipedia and dbpedia URI's is as follows:
For
http://en.wikipedia.org/wiki/Spain
DBPedia uri is:
http://dbpedia.org/resource/Spain
So to find out the categories for the above
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?categoryUri ?categoryName
WHERE {
<http://dbpedia.org/resource/Spain> dcterms:subject ?categoryUri.
?categoryUri rdfs:label ?categoryName.
FILTER (lang(?categoryName) = "en")
}