sparqlrdfsemantic-webdbpediatriples

Sparql- Number Of Entities and Instances?

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?

Solution

  • 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.