I think Drupal 7 stands a chance of being a killer semantic app, it’s the next version of a CMS with a sizeable install base and when the release is final and everyone starts upgrading suddenly tons of sites will be automatically exposing RDF in the form of embedded RDFa without any intervention on the … Read more
The first two of these, DatatypeProperty and ObjectProperty, describe what kind of values a triple with the property should have. Datatype properties relate individuals to literal data (e.g., strings, numbers, datetimes, etc.) whereas object properties relate individuals to other individuals. Something like hasAge would typically be a datatype property, since an age is a number, … Read more
Context Datatourisme is a platform that allows to publish (via the Producteur component) and to consume (via the Diffuseur component) POI-related open data. It seems you have linked to a particular application developed over Diffuseur with a help of GraphQL Voyager. The application illustrates capabilities of the GraphQL API exposed by Diffuseur. The API documentation … Read more
If you’re using Java and Jena’s ARQ, you can use ARQ’s extensions for aggregates. Your query would look something like: SELECT ?tag (count(distinct ?tag) as ?count) WHERE { ?r ns9:taggedWithTag ?tagresource. ?tagresource ns9:name ?tag } LIMIT 5000 The original SPARQL specification from 2008 didn’t include aggregates, but the current version, 1.1, from 2013 does.
I’m not entirely sure why you say SPARQL doesn’t supply ‘the basic logic operators’, because your own examples clearly show that it does: it provides logical-OR (||) and logical-AND (&&) as part of FILTER conditions, and disjunctive graph patterns using UNION (of course, conjunctive graph patterns need no special syntax). Other variations of OR-like constructs … Read more
The viewpoint of the CTO of a company that extensively uses RDF Triplestores commercially: Schema flexibility – it’s possible to do the equivalent of a schema change to an RDF store live, and without any downtime, or redesign – it’s not a free lunch, you need to be careful with how your software works, but … Read more
The best explanation is by example. Try googling for all cars advertised on the web with engines smaller than 2.0 litres that run unleaded, and have an mp3 connection and can been seen in a showroom conveniently accessible by public transport from my house. Google just won’t be able to help you with that query, … Read more
Well, the obvious first start is to look at the classes and properties present in the data. Here is how to see what classes are being used: SELECT DISTINCT ?class WHERE { ?s a ?class . } LIMIT 25 OFFSET 0 (LIMIT and OFFSET are there for paging. It is worth getting used to these … Read more
The main difference between graph databases and triple stores is how they model the graph. In a triple store (or quad store), the data tends to be very atomic. What I mean is that the “nodes” in the graph tend to be primitive data types like string, integer, date, etc. Relationships link primitives together, and … Read more