Re: [dotNetRDF-Support] Ontology API example

[Rob V. <rv...@vd...>]

Hi Ian

Thanks for the feedback, I have updated the example to note that 
Ontology.rdf is an example filename and you should substitute your own 
filename there.

The NullReferenceException on the GetTriplesWithSubjectPredicate() call is 
due to the fact that someclass2 is populated using the GetUriNode() method 
which returns null if there is no such node in the Graph, either check 
someclass2 for null as I have done in the updated example or use 
CreateUriNode() instead.

With regards to the formatter parameter that should be optional, INode's 
have an overload of ToString() which takes the formatter parameter to allow 
you to control exactly how the Node is converted into a String.  But they 
should also have the default ToString() method which all .Net objects have. 
 Not sure if this is some VB compiler specific issue as I do all my coding 
in C# these days and the C# compiler doesn't insist on the formatter 
parameter, will look into this and get back to you.

In the meantime if the compiler insists on the formatter parameter I would 
use an NTriplesFormatter e.g.

Dim   formatter  As   VDS.RDF.Writing.Formatting.INodeFormatter
formatter = new VDS.RDF.Writing.Formatting.NTriplesFormatter();

If you have any further questions/issues please let me know

Rob Vesse

----------------------------------------
From: "Ian R Fry" <ia...@fr...>
Sent: 10 April 2011 11:33
To: dot...@li...
Subject: SPAM-LOW:  [dotNetRDF-Support] Ontology API example 

In the second version (showing detail Graphs and Triples) I am getting some 
errors. 
Note I have used VB.Net for a web applicaiton 
  
a)   	Console.WriteLine("Super Class: " + t.Object.ToString());
  	The tostring requires a "formatter" parameter which I have never seen 
before  
  
b) foreach (Triple t in g.GetTriplesWithSubjectPredicate(someClass, 
subClassOf))
 
gives  
Object reference not set to an instance of an object.  


I have imported all the classes.


Here is the code
 

 Dim   g1 =  New   Graph() 
 

FileLoader.Load(g, Server.MapPath( "data/Ontology.rdf"  )) 
 

 Dim   someclass2, subclassof  As   INode 
 

someclass2 = g.GetUriNode( New   Uri( "http://example.org/someClass"  )) 
 

 Dim   t1, t2  As   Triple 
 

 Dim   formatter  As   VDS.RDF.Writing.Formatting.INodeFormatter 


subclassof = g.CreateUriNode( New   Uri(NamespaceMapper.RDFS +  
"subClassOf"  )) 
 

 For    Each   t1  In   g.GetTriplesWithSubjectPredicate(someclass2, 
subclassof)  <---- error  
 

Response.Write( "<br>Super Class: "   + t1.Object.ToString(formatter)) 
<---- compiler complains if no formatter  
 

 For    Each   t2  In   g.GetTriplesWithPredicateObject(subclassof, 
someclass) 
 

Response.Write( "<br>Sub Class: "   + t2.Subject.ToString(formatter)) 
 

 Next  
 

 Next  


   


love the product though  


   


Ian Fry  


Fry Systems