Chronos: A Tool for Handling Temporal Ontologies in Protégé Alexandros Preventis, Polyxeni Marki, Euripides G.M. Petrakis, Sotirios Batsakis Dept. of Electronic and Computer Engineering Technical University of Crete (TUC)

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.

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.

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.

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

N-ary Example

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

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).

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

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

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

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

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

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))

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).

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

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

User Interface

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

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