The OWLGrEd ontology editor allows graphical visualization and authoring of OWL 2.0 ontologies using a compact yet intuitive presentation that combines UML class diagram notation with textual Manchester syntax for class expressions. Here we show, how to integrate OWLGrEd with ontology module mechanism from OWL API to obtain on-demand ontology fragment visualization that is essential for many existing large ontologies that do not fit in a single reasonably perceivable UML class diagram.
Intuitive ontology visualization is a key for their learning, exchange, as well as their
use in conceptual modeling and semantic database schema design. A number of tools
and approaches exist for rendering and/or editing OWL [
The main focus of this demo is on using the compact UML-style notation, offered by OWLGrEd, on large ontologies that do not fit within any reasonably-sized class diagram, or whose rendering appears to be too complicated due to a kind of “spider web” effect produced by many classes and relations. Its key idea consists in splitting the ontology into meaningful fragments of conceivable size and then visualizing each of the fragments in a separate diagram .
OWLGrEd already has the means to partition ontology into sub-diagrams (fragments) when authoring or reengineering an existing ontology. But there was no way to automatically partition an ontology that is imported into OWLGrEd for visualization. In this demo we will present an extension to OWLGrEd visualization capabilities, that allows automatic partitioning of an ontology into logical fragments. The addition is based on Automatic Decomposition [11] that was recently implemented in the OWL API1. The decomposition is based on signatures, i.e. for each fragment a user selects some entities that should be included in the fragment. Then the fragment is extended with all the logically relevant axioms for these entities. Finally all the fragments are rendered graphically in the OWLGrEd editor.
The demonstration shows (i) working with OWLGrEd tool to render and author OWL ontologies (ii) OWLGrEd extension to automatically partition ontology into logical overlapping fragments based on fragment signatures. 2
OWLGrEd1 provides a complete graphical notation for OWL 2 [
• fields in associations and attributes for equivalent, disjoint and super properties and fields for property characteristics, e.g., functional, transitive, etc.; • anonymous classes containing equivalent class expression but no name (we show graphically only anonymous classes that need to have graphic representation in order to be able to describe other ontology concepts in the diagram); • connectors (as lines) for visualizing binary disjoint, equivalent, etc. axioms; • boxes with connectors for n-ary disjoint, equivalent, etc. axioms; • connectors (lines) for visualizing object property restrictions some, only, exactly, as well as cardinality restrictions.
OWLGrEd provides option to specify class expressions in compact textual form rather than using separate graphical element for each logical item within class expression. If an expression is referenced in multiple places, it can optionally be shown as an anonymous class. An anonymous class is also used as a base for property domain/range specification, if this domain/range is not a named class.
Figure 1 illustrates some basic OWLGrEd constructs on a simple mini-University
ontology, including different notation options for EquivalentClasses assertion, object
property restriction and a comment. The notation is explained in more detail in [
name:string{func}
<<Comment>> "All persons, including teachers and students"
Professor <<equivalent>> AcademicStaff =Teacher
Person
"Al persons, including teachers
and students"
key = personID
personName:string{<name}
personID:string[
AcademicProgram programName:string{<name} belongsTo enrolled {>takes o belongsTo} includes relates coursCeNoaumrsee:string {<name}
isTakenBy takes {<relates} 1..10
isTaughtBy teaches {<relates} {<>takes}
<teaches some MandatoryCourse teaches some [1..*] MandatoryCourse
The OWGrEd editor offers ontology interoperability (import/export) functionality
with the Protégé 4.2 ontology editor [
Protégé to analyze and possibly submit it to other ontology processing tools) - ontology visualization (an ontology that is imported from Protégé is displayed graphically to obtain a comprehensible visual view on it). 3 Visualizing Fragments of Ontology The graphical form is ideal for understanding small ontologies, but for large ontologies it fast becomes overwhelming because of too many line crossings. For visualization of the ontology in the form of fragments an issue is to describe the fragments to be visualized since manual enumeration of all axioms to be included into a fragment would clearly be infeasible. Recently there has been work on signaturebased automatic decomposition [11] of ontologies that allows specify ontology modules just in terms of their “core” terms/entities. The decomposition then finds all the axioms that are logically relevant for the given entities.
We have extended OWLGrEd editor with the Automatic Decomposition feature. A user can specify either a single ontology fragment, or a list of fragments covering the whole ontology that is to be visualized. The automatic decomposition then finds all the relevant axioms for each specified fragment thus allowing OWLGrEd showing the fragments visually in a graphical form.
As an example consider the schema.org ontology. It consists of about 300 classes, 110 object properties, 70 data properties and 310 subclass assertions. The ontology is clearly too large to be easily perceived as a single diagram. However, it would be feasible as well as meaningful to visualize fragments of the. For example, in the Figure 2 is shown a fragment that is centered on entities “Event”, “Product” and “Person”. Once the user has specified such an entity list, the tool automatically finds the relevant axioms for these entities and then shows this fragment graphically. It is possible to specify any number of such fragment signatures at a time and the tool will create visualization for each of them.
The experiments we have performed allows us to judge that the offered approach of combining of the traditional OWLGrEd ontology visualization means with ontology decomposition techniques would be a useful tool for the semantic technology community in ontology schema structure representation.
Thing{owl}
model Product itemOfered productID brand manufacturer performers at endees homeLocation alumniOf workLocation worksFor af iliation nationality memberOf
subEvents superEvent endDateEvent
startDate events founders editor actors musicGroupMember il ustrator producer alumni employees director
EducationEvent BusinessEvent SportsEvent SocialEvent VisualArtsEvent TheaterEvent DanceEvent
Festival UserInteraction LiteraryEvent ChildrensEvent MusicEvent ComedyEvent Fig. 2. Automatically extracted fragment of schema.org ontology based on a signature “Event, Product, Person”.