Chronos: A Tool for Handling Temporal Ontologies in Protégé

1. Chronos: A Tool for Handling TemporalOntologies in Protégé AlexandrosPreventis, PolyxeniMarki, Euripides G.M. Petrakis, Sotirios Batsakis Dept. of Electronic and Computer Engineering Technical University of Crete (TUC)

2. OWL • OWL (Web Ontology Language) is a language that can be used to describe the classes and relations between them. • more expressive than XML, RDF and RDF-S • allows to reason about the entities and check whether or not all statements and definitions are mutually consistent • OWL directly supports binary relations.

3. Dynamic Ontologies • Represent concepts that occur and evolve in time • A company will be established, hire personnel and develop products • The relation “employs" and its inverse are ternary.

4. OWL-Time Ontology • OWL-Time is an OWL ontology of temporal concepts. It provides a vocabulary for describing: • topological relations between temporal entities (instants, intervals) • information about durations • It provides no means of representing information that changes in time.

5. Temporal Representations • Models for representing temporal information: • Temporal Description Logics (TDLs) • Versioning • Reification • 4D-Fluents (Welty 2006 & Batsakis 2011) • N-ary Relations

6. N-ary Example

7. Protégé • Protégé is a free, open-source editor platform for handling ontologies: • enables users to build ontologies for the Semantic Web, in particular in the W3C's Web Ontology Language (OWL) • Can be extended by means of a plug-in architecture and a Java-based Application Programming Interface (API) for building knowledge-based tools and applications

8. Problem • The creation of a temporal ontology, or the conversion of a static ontology to temporal can be a very complex, time-consuming and error-prone procedure. • Involves intermediate relations and properties • The temporal properties in N-ary apply on intermediate relations • The user must have very good knowledge of the underlying (N-ary in our work) representation model. • There is no tool for crafting temporal concepts in ontologies easily (i.e., similarly to static ontologies).

9. Chronos • We present Chronos, a Plug-In for the Protégé editor (version 4.1,supporting OWL 2.0) that: • handles temporal ontologies similarly to static ones • supports restriction checking on temporal properties, classes and individuals • supports reasoning over temporal ontologies using the Pellet reasoner with Protégé • its interface is consistent with the layout of the default Protégé tabs • The user need not be familiar with the N-ary model

10. Modified entities • Although it is feasible to create a temporal ontology using the standard Protégé tabs, it is difficult to define temporal properties and restrictions. • Changes that are applied during the conversion of: • Object Properties • Data Properties • Individuals • Classes

11. Object Properties • The changes that will take place in order to convert an object property to temporal are: • Property domain and range • Event class is related to the Interval with the object property during

12. Data properties • The changes that will take place in order to convert a data property to temporal are: • Property domain • creation of an object property (named by the data property, and followed by “OP") which will relate the static data property's domain to the Event class. • Event class is related to the Interval with the object property during

13. Individuals • When a property is converted to temporal, all its instances have to be converted as well.

14. Value constraints • owl:allValuesFrom Company employs only Programmer In the case where `employs' is temporal object property, the constraint is: • Company employs only (Event and (employs only Programmer)) • owl:someValuesFrom Company employs some Programmer In the case where `employs' is temporal object property, the constraint is: • Company employs some (Event and (employs some Programmer))

15. Cardinality Constrains (1/2) • owl:maxCardinality Company employs max 2 Employee • owl:minCardinality Company employs min 2 Employee • owl:cardinality Company employs exactly 2 Employee • owl:FunctionalProperty A functional property is a property that can have only one (unique) value y for each instance x, i.e. there cannot be two distinct values y1 and y2 such that the pairs (x, y1) and (x, y2) are both instances of this property. • John worksFor Apple • A temporal functional property can have only one value in each time interval during which the property holds. This is implemented by adding a SWRL rule to the ontology (Batsakis2012).

16. Cardinality Constrains(2/2) • owl:inverseFunctionalProperty If we state that P is an owl:InverseFunctionalProperty, then this asserts that a value y can only be the value of P for a single instance x, i.e. there cannot be two distinct instances x1 and x2 such that both pairs (x1, y) and (x2, y) are instances of P. • Apple employs John • When a temporal property is inverse-functional the object uniquely determines the subject for each time instant. • If a temporal property P is transitive and (x, y, interval1) is an instance of P and (y, z, interval2) is an instance of P, then we can infer that (x, z, interval1 ⋂ interval2) is also an instance of P. In our implementation the transitivity between instances of a temporal property takes place only if those instances hold for same time intervals

17. Class Conversions • Chronos provides a convenient way to convert multiple object and data properties to temporal. This function converts: • the object and data properties that relate members of the selected class • the object and data properties where this class appears as a Domain • the restrictions where one of these object or data properties appear in

18. User Interface

19. Conclusions • Chronos, is a tab plug-in for Protege editor that facilitates the creation and editing of temporal OWL 2.0 ontologies. • The temporal concepts as well as the properties that evolve over time are represented by means of the N-ary Relations model, that is a W3C recommendation. • It applies on restrictions on temporal properties, which have different semantic meaning than those applied on static properties. • The user does not have to be familiar with the peculiarities of the temporal representation model, thus making the manipulation of temporal entities as easy as if they were static. • Available at: www.intelligence.tuc.gr/prototypes

20. Thank You Questions?