Advanced UML Style Visualization of OWL Ontologies Jūlija Ovčiņņikova*, Kārlis Čerāns julija.ovcinnikova@lumii.lv, karlis.cerans@lumii.lv Institute of Mathematics and Computer Science, University of Latvia Raina blvd. 29, Riga, LV-1459, Latvia Abstract. The OWLGrEd ontology editor allows graphical visualization and au- thoring of OWL 2.0 ontologies using a compact yet intuitive presentation that combines UML class diagram notation with textual OWL Manchester syntax for expressions. We describe here the approaches available for ontology presentation fine tuning within the OWLGrEd editor, namely the ontology visualization op- tion framework and the editor plug-in mechanism together with concrete plug- ins aimed to enhance the ontology presenting and editing experience. Keywords: OWL, OWLGrEd, UML-style ontology visualization, ontology vis- ualization options 1 Introduction Presenting OWL ontologies [1] in a comprehensible form is important for ontology designers and their users alike. The graphical form in general and UML class diagram notation in particular offers an option of basic visual ontology construct presentation that allows linking together constructs that are related in the ontology (e.g. an object property can be depicted as a line connecting its domain and range class boxes). UML class diagrams need to be extended to cope with full OWL 2.0 construct modeling. This is solved in different graphical notations in different ways. So, ODM [2], defines a UML profile for ontology presentation and OWLGrEd [3] and TopBraid Composer [4] integrate OWL Manchester Syntax [5] for presenting advanced OWL constructs in tex- tual form. The uniqueness of OWLGrEd lies in its combined ability to lay out an ontol- ogy that is imported or created in the editor in a compact graphical UML-style form, and make further manual ontology editing/adjustment. VOWL [6] visualizes ontologies by another approach using graphical primitives both for object and data property presentation, so obtaining a more uniform ontology presentation in a dynamic, yet read- only, graph-like form. The VOWL presentation of the same ontology will also typically require more graphical elements, than OWLGrEd. The real strength of ontology presentation in an editor like OWLGrEd comes from the user’s ability to fine-tune the ontology diagram after its automated rendering to obtain documentation-ready ontology presentations. Such a fine tuning may involve the * Supported, in part, by Latvian State Research program NexIT project No.1 “Technologies of ontologies, semantic web and security”. 136 Advanced UML Style Visualization of OWL Ontologies diagram object repositioning, as well as its re-structuring up to full ontology editing facilities available in the tool (including e.g. manual deletion of irrelevant information). In order to achieve a high quality ontology presentation in the tool, even in the pres- ence of manual fine tuning options available, the quality of first ontology diagram cre- ated upon the import of the ontology into the tool still remains very important. Since the UML diagrams, as well as the OWLGrEd notation allow for different presentations of the same semantic elements (e.g. a graphical and textual one), and different ontolo- gies may correspond to different desirable ontology presentation options, we describe here a re-factored ontology visualization option framework offering a number of choices that the user can make already before importing the ontology into the tool. We describe here also a number of OWLGrEd plugins that can be used for diagram refactoring services, as well as its structural and semantics extensions. This part of work extends the earlier authors’ work on domain specific ontology visualizations [7,8] (this paper describes new re-factoring services plug-in, as well as reviews the plug-in mech- anism and concrete plugin architecture from the ontology visual presentation perspec- tive). The editor plugins described here are included in the OWLGrEd tool download and can be activated on-demand for concrete projects. The OWLGrEd editor with pre- installed configuration, as described here, is available at http://owlgred.lumii.lv/pp. 2 OWLGrEd Notation and Editor OWLGrEd (http://owlgred.lumii.lv/) provides a graphical notation for OWL 2 [1], based on UML class diagrams. OWL classes are typically visualized as UML classes, data properties as class attributes, object properties as association roles, individuals as objects, cardinality restrictions on association domain class as UML cardinalities, etc. The UML class diagrams are enriched with new extension notations, e.g. (cf. [3,9]):  fields in classes for equivalent class, superclass and disjoint class expressions writ- ten in Manchester OWL syntax [5];  fields in association roles 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;  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. Fig. 1 contains a simple demonstration fragment of Latvian Medicine Registries ontol- ogy [10] in OWLGrEd notation, illustrating the class, data and object property, as well as subclass, sub-property and object property restriction notation, different ways of dis- joint classes notations, class-level inline comments and ontology level annotations. The OWLGrEd tool allows both for ontology authoring (with option to save the on- tology in a standard textual format) and ontology visualization that includes automated ontology diagram formation and layouting step, followed by optional manual diagram fine tuning to obtain the highest quality rendering of the ontology. 137 Advanced UML Style Visualization of OWL Ontologies treatedIllnessCase IllnessCase <> IllnessTreatment "Illness case Person and patient patient personID:string ontology {disjoint} dateOfBirth:dateTime diabPatient {> only DiabetesTreatment Fig. 1. Demo fragment of Latvian Medicine Registries Ontology 3 Ontology Visualization Parameters The UML notation provides several options for presenting its semantic elements in dif- ferent visual ways. This principle is kept also in OWLGrEd by including both graphical and textual notations for such semantic elements as subclass relations, object property relations, annotations and object properties as association roles or as attributes. The automatic ontology visualization in OWLGrEd by default shall use the graphical notation, if there is no clear reason for switching to textual one. Fig. 2 shows a larger fragment of Medicine Registries Ontology in a graphical notation for all object proper- ties and object property restrictions, and with separate disjoint classes axiom rendering. treatedIl lnessCase IllnessCase Person personID:string patient treatingD octor dateOfBirth:dateTime diabPatient {> traumaPatient cancerPatient illnessR egDoctor Doctor {> only treatedIl lnessCase only Trauma MedicalEstablishement <> estNam e:string estType :string treatme ntPlace IllnessTreatment traumaD iagnosis cancerD iagnosis treatedD iagnosis {> diabDia gnosis {> diagnDe scr:string traumaTrDiagnosis {> personID:string illnessR egDoctor:Docto r treatingD octor:Doctor Diagnosis dateOfBirth:dateTime illnessD iagnosis:Diagn osis treatme ntPlace:Medica lEstablishemen t diagnCo de:string patient:Person treatedD iagnosis:Diagn osis diagnDe scr:string treatedIl lnessCase:Illne ssCase Trauma {disjoint} {disjoint} traumaR egDoctor:Doctor{> cancerTrDiagnosis:Dia gnosis{> Doctor Diabetes doctorN ame:string diabReg Doctor:Doctor{> {disjoint} traumaR egDoctor:Doctor{> cancerR egDoctor:Docto r{> diabReg Doctor:Doctor{