Removing individuals & properties from RDF

owlrdfrowlexsemantic-web

I have a RDF file in my semantic web project and I use Rowlex for manipulating it.
I've needed to remove an individual from RDF, so I used

<RDFDoc instance>.RemoveIndividual(new OwlThing(<individual URI>, <RDFDoc instance>));

With this code, I had my individual gone, but it's properties still remained. So I figured out that I should remove it's properties first. Besides I didn't find a command for removing all properties together. So, Question1: is there a way to remove an individual with all it's properties? or, can I remove all properties in one line of code and not one by one? And how can I remove properties with multiple values. For instance three StudyLists, in example down page.

On the other hand, when I tried to remove a property, for example 'useSudyList' from student individual, by this code:

student.RemoveuseStudyList(student.useStudyList);

I found my RDF file:

<Ontologyowl:Student rdf:about="ehsanm">
//other properties
    <Ontologyowl:useStudyList>
        <Ontologyowl:StudyList rdf:about="stdl184516"/>
    </Ontologyowl:useStudyList>
</Ontologyowl:Student>

… became like this:

<Ontologyowl:Student rdf:about="ehsanm">
    //other properties  

</Ontologyowl:Student>
<Ontologyowl:StudyList rdf:about="stdl184516"/>

Thus the property was thrown out. I don't have this issue with literal properties. Question2: what's the problem?

Thanks for your attention, and help, in advance.

Best Answer

Your question has nothing to do with ROWLEX but it is a typical graph problem: if you delete a node, how far do you cascade the deletion? When you delete a property with a literal, the case is easy as there is no continuation of the graph. When you delete a property pointing to another node should you delete the node? Deletion in your example looks obvious because your graph contains neither circular reference, nor shared relationships.

Imagine the following graph: You have 3 persons: A (Adam), B (Bill), and their father F (Fred). You have fathership relationship between A - F and B - F. You delete relationship between Adam and his father. Should you delete the father node and bring Bill into an inconsistent (orphan :) state? The answer here is "no". You delete the relationship only.

In UML diagrams, you have the option in aggregation relationship to differentiate between "possessing" and "shared". It is expressed in the color (black or white) of the diamond at the end of the line. In relational databases, you can define or ignore "Cascade delete" over foreign keys. They represent the same concept. Unfortunately, RDF does not offer this extra metadata over a property. Had RDF have this information available, we could determine when and how far should we cascade deletion over the graph. But we don't. That sets the case up for the bad news: you are on your own, you can implement the deletion as you see fit.

Related Solutions

R – Some functionalities of Rowlex

1) Saving: You have various ways to persist your RdfDocument. You have 2 choices on the format: RDF/XML or N3. Based on your choices, you can invoke any the following methods:

RdfDocument rdfDoc = new RdfDocument();
// Populate the document with new individual
// ...
// Alternatives to save the document
XmlDocument xml = rdfDoc.ExportToRdfXml();
xml.Save("C:\\myRdfDoc.rdf");
// or
rdfDoc.ExportToRdfXml("C:\\myRdfDoc.rdf");
// or
rdfDoc.ExportToN3("C:\\myRdfDoc.rdf");
// or 
string n3 = rdfDoc.ToN3();
string rdfXml = rdfDoc.ToRdfXml();
// and save the strings into a text file yourself

It is important to understand: you always save the RDF document which represent your entire RDF graph. You do not save an individual!

2) Removing an individual from an RdfDocument:

RdfDocument rdfDoc = new RdfDocument();
// Let us assume that you have an ROWLEX generated class called "Car"
// Let us create a Car individual first, then remove it.
Car car = new Car("ABC-123", rdfDoc); // added
rdfDoc.RemoveIndividual(car); // removed

3) Adding/Removing/Editing properties

Car car = new Car("ABC-123", rdfDoc); 
// We inject a new triple into the document by this
car.LastMaintenance = new DateTime(2008,04,18); 
// Editing the property:
car.LastMaintenance = new DateTime(2009,05,11); 
// For removing, you need to use the full-version of 
// the generated class instead of the light-version:
Car_ sameCar = rdfDocument.GetIndividual(car.ID, Car.Uri, false) as Car_; 
sameCar.RemoveLastMainenance(sameCar.LastMaintenance);

R – Assigning multiple values to a property

For every ontology class, ROWLEX generates two .NET classes a "full" and a "light" one. The two autogenerated classes are differentiated by naming convention. If your OWL class is named "Student" than the light class will be named "Student", too. The full class is named "Student_". They are completely exchangeable with one another, the sheer purpose of having two is convenience. The full class contains every possible methods/properties you need. The light class contains only the most frequently used ones. The problem with full classes that they get really crowded. For every single OWL property you will get 10 (!) properties and methods for in your .NET class:

Add (typesafe)
Add (not typesafe)
Remove (typesafe)
Remove (not typesafe)
Replace (typesafe)
Replace (not typesafe)
Non array property (typesafe)
Non array property (not typesafe)
Array property (typesafe)
Array property (not typesafe)

If you have just 5 OWL properties to cater for, the autogenerated .NET full class will have 5x10 methods/properties. These high number of members easily defeat the usefulness of intellisense. Hence generally the use of light classes are recommended.

On the light class, you have only the non array property implemented (unless cardinality restrictions explicitly direct otherwise) and that property internally calls the replace method. In your case you need to use the full class.

This is how you get and use the full class (I did not verify the code):

Student_ student = (Student_)rdfDoc.GetIndividual(uri_stu, Student.Uri, false);
student.AddstudyMemberOf(new Project(uri_proj, rdfDoc));

Best Answer

Related Solutions

R – Some functionalities of Rowlex

R – Assigning multiple values to a property

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