Web 3 vs Web 2

[tina sani]

Greetings

I want to ask how Semantic Web provides meaning to our data? How it differs
from the current web.
I will appreciate if some one provide with a simple examples: If we write
an Ontology and develop Semantic Web application, how it differs from a
simple Java application (without Semantic Web) and a traditional database
system?

Re: Sparql Update: Insert a property whose value is a calculated average

[Andy Seaborne]

On 04/06/17 18:47, Aya Hamdy wrote:

Hello,

I wanted to add a property called avgSpeed to an instance of a class called
FlowSensor. This property should be the average of the values of the
property vehicleSpeed attached to instances of the class Vehicle.

I read that SPARQL update allows doing this. However, I cannot reach the
syntax for doing the* averaging of values* or for building the *SPARQL
Update *query using jena with eclipse on the jena website.

If Jena indeed supports doing what I intend to do then can someone point
out some sources to guide me in my attempt?

Best Regards,
Aya



Calculate the average in a nested select so somethign like (you'll have 
to fix this up):


INSERT {
  :avgSpeed ?avg
   }
WHERE {
   SELECT (AVG(?speed) AS ?avg) {
   ?v rdf:type :Vehicle ;
  :vehicleSpeed ?speed
   }
}

By the way - it is better to more concrete in your description - actual 
data for example.

Sparql Update: Insert a property whose value is a calculated average

[Aya Hamdy]

Hello,

I wanted to add a property called avgSpeed to an instance of a class called
FlowSensor. This property should be the average of the values of the
property vehicleSpeed attached to instances of the class Vehicle.

I read that SPARQL update allows doing this. However, I cannot reach the
syntax for doing the* averaging of values* or for building the *SPARQL
Update *query using jena with eclipse on the jena website.

If Jena indeed supports doing what I intend to do then can someone point
out some sources to guide me in my attempt?

Best Regards,
Aya

Re: Cloning model with blank nodes

[Martin G . Skjæveland]

Thanks, this is very useful.

Martin

On 03/06/17 17:34, Andy Seaborne wrote:

Hi Martin,

There's nothing the API IIRC.

The crude way is to write out to byte array and parse it.


Here's my (limited testing) attempt: I chose to work with the Graph API 
because if you use the Model API there is both up and down casting to 
match new Statement(Resources, Predicate, RDFNode).




public static void main(String... args) {
 Model mSrc = ModelFactory.createDefaultModel();

 RDFDataMgr.read(mSrc, "some-suitable-test-data.nt");

 Model mDst = ModelFactory.createDefaultModel();

 Map map = new HashMap<>();
 Iter.asStream(mSrc.getGraph().find(Triple.ANY))
 .map(t->clone(map, t))
 .forEach(mDst.getGraph()::add);

 // The N-triples writer uses the internal ID for the label.
 RDFDataMgr.write(System.out, mSrc, Lang.NT);
 System.out.println("");
 RDFDataMgr.write(System.out, mDst, Lang.NT);
}


public static Triple clone(Map map, Triple t) {
 return Triple.create(clone(map, t.getSubject()),
  clone(map, t.getPredicate()),
  clone(map, t.getObject()));
}

public static Node clone(Map map, Node n) {
 if ( ! n.isBlank() )
 return n;
 // Just (_)-> in Java9
 return map.computeIfAbsent(n, NodeFactory::createBlankNode);
}



On 02/06/17 17:14, Martin G. Skjæveland wrote:

Hi,

I would like a method  Model clone (Model) that creates a copy of a 
model such that any blank nodes in the copy are kept apart from the 
source.


The test case below illustrates the intended use: adding the clone of 
a model back into the model should increase the size of the model, if 
the model contains blank nodes.


Is there such a method in the API, or need I invent my own? If so, any 
suggestion of an optimal way will be greatly appreciated.


I have tried by adding a model into a fresh model. My other 
suggestions are to iterate over all blank nodes in a model and replace 
all instances with a fresh node, or to use a SPARQL query CONSTRUCT { 
?s ?p ?o } WHERE { ?s ?p ?o }.


Thanks!
Martin


import static org.junit.Assert.*;

import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.ModelFactory;
import org.apache.jena.rdf.model.ResourceFactory;
import org.apache.jena.vocabulary.OWL;
import org.apache.jena.vocabulary.RDF;
import org.junit.Test;

public class ModelsTest {

   @Test
   public void shouldCloneModel () {

 // create the model:  [] a Thing .
 Model source = ModelFactory.createDefaultModel();
 source.add(ResourceFactory.createResource(), RDF.type, OWL.Thing);

 // OK
 assertEquals(1, source.size());

 // clone
 Model copy = clone(source);

 // OK
 assertEquals(1, copy.size());


 // adding cloned copy back into source
 source.add(copy);

 // Fails with current implementation
 assertEquals(2, source.size());
   }

   public Model clone (Model source) {
 Model copy = ModelFactory.createDefaultModel();
 copy.add(source);
 return copy;
   }
}