Web Ontologies with Protégé

First Steps

• Download the Protégé ontology editor. Do not use WebProtégé.
• Download the DBPedia ontology (DBO) and store it in a .owl file (e.g. dbo.owl).
• Open Protégé and click on the menu item File > Open, to open the .owl file. In the “Active ontology” tab, in the “Ontology metrics” panel, you should see statistics about DBO (~1400 classes, ~800 object properties and ~1100 datatype properties, among others).

As shown in this panel, OWL definitions are called axioms. Axioms can apply to classes or properties. In OWL, a difference is made between object properties and data properties. Object properties are properties with a URI as value; data properties are properties with a literal as value. For instance, in the following two triples, op is an object property and dp is a data property: <s> <op> <o> ; <dp> "o" .

• Click on the menu item File > Save as … and choose "Turtle Syntax" to save DBO in a .ttl file.

Exploring the DBpedia Ontology

• Move to the “Entities” tab. The left panel shows the class hierarchy defined in DBO. Using the "Search..." button in the top right corner of the Protégé window, search for dbo:University. After clicking on the correct entity, you should see information about this class in the right panels ("Annotations", "Description").

• In the "Class hierarchy" panel, you should see two classes called "university". What is their full URI? Is there a difference between the two, in ontological terms?
• dbo:University is aligned with concepts from Wikidata and schema.org. Give the URI of these external concepts. Is the Wikidata concept ontologically equivalent to the schema.org concept?
• In the "Annotations" panel, you should see a list of key/value pairs, such as multilingual labels (rdfs:label) and provenance data (prov:wasDerivedFrom). Give the Turtle equivalent of these key/value pairs. You can look up the answer in the .ttl file you previously created or click on the rightmost button next to the key/value pair (). As to labels, report only the one in French.
• The dbo:University class was automatically generated from a Wikipedia template (University infobox). The mapping, documented here, specifies that universities can have a president. With the "Search..." button, navigate to the corresponding DBO property. Is it an object or a data property?

• In the "Description" panel of dbo:president, you should see that the range of this property is dbo:Person. Give the Turtle equivalent of this definition.
• In the same panel, you can see that the "Domains" field has no value although, by construction, the domain of the property should at least include dbo:University. Why is the class not appearing as domain of dbo:president?

Defining an Ontology

OWL is expressive enough to capture UML class diagrams and entity-relationship (ER) diagrams. In this part, you will translate an ER diagram to OWL. If you have doubts about the different OWL constructs, refer to the OWL 2 primer document.

• Translate the above diagram into OWL. Entities (blue boxes) translate to classes, relationships (diamonds) and attributes (cyan ellipses) translate to properties. Circles labeled with "d" indicate that target classes are disjoint subclasses of the source class. Make sure you take this constraint into account, as well as cardinalities and primary key constraints (underlined attributes).
• subOrganizationOf and subOrganization are in fact the same relationship (the diagram has a typo). Define them as equivalent properties in OWL.
• In the ER diagram, there is no overarching class for all organizations. Introduce a class to fill this gap. Should this class be the disjoint union of all university organizations?
• All properties of the form *DegreeFrom have the same structure: their range is a university. Add a new super-property in your ontology to properly capture this structure.
• In universities, every professor who is the head of a department is necessarily a full professor. Add an OWL axiom capturing this statement.