UbisEditor 3.0: Collaborative Ontology Development on the Web Matthias Loskyll Dominikus Heckmann Ichiro Kobayashi Saarland University DFKI GmbH Ochanomizu University 66123 Saarbrücken, Germany 66123 Saarbrücken, Germany Ohtsuka Bunkyo-ku Tokyo matthias@xantippe.cs.uni- heckmann@dfki.de 112-8610, Japan sb.de koba@is.ocha.ac.jp ABSTRACT methods. Ontologies continuously become larger and more complex, With the increasing importance of ontologies, several on- and therefore more and more difficult to maintain, to edit tology editors have been developed. Two of the currently and to develop by one single person or a small group of most popular ones are Protégé [7] and Swoop [3]. However, experts. The basic principle of Web 2.0, on the other hand, there are only few online editors for ontologies available. is to use the willingness and knowledge of a huge community Recently, a web-based version of Protégé called WebProtégé of users to create rich user-generated content. The obvious [11] was released. An evaluation of different tools for col- idea that comes to mind is to combine the technologies of the laborative ontology development during the CKC challenge Semantic Web with the trend of the Web 2.0. We present [6] showed that users prefer Web interfaces for editing tools. UbisEditor 3.0, an easy-to-use web tool for the creation and Our prototype called UbisEditor uses Ajax technologies to manipulation of structured collective knowledge represented load and send required data on demand such that it provides as ontologies. This web ontology editor is realized as part of a lightweight and efficient way of performing ontology edit- the UbisWorld project and already supports ontology editing ing on the Web. Other differences of our approach compared techniques like adding new concepts, renaming and deleting, with related work are: our ontology is stored in a database but also the creation of personalized ontology views. structure, editing can be performed using a context menu, we already have a role-based rights management, and we Categories and Subject Descriptors provide multilingual renaming of concepts. M.1 [Knowledge Engineering Methodologies] ; H.5 [Information Interfaces and Presentation]: User Interfaces General Terms Semantic Web, Web 2.0 Keywords online ontology editing, collaborative ontology building, on- tology views 1. INTRODUCTION The characterization of Web 3.0 used in this paper is based on [12], in which Wahlster and Dengel define Web 3.0 as the Figure 1: The trend of Web 3.0 combining Web 2.0 integration of Semantic Web technologies with the princi- and Semantic Web ples of Web 2.0. UbisEditor 3.0 perfectly fits to this defini- tion of Web 3.0 because it combines ontology development, Ontology segmentation or the creation of ontology views which forms the backbone of Semantic Web, together with is an important issue. Since many ontologies constantly the community approach of Web 2.0 (see Figure 1). Re- grow in size and are therefore more and more difficult to cently, the meaning of Web 3.0 has been extended to an understand, maintain and edit, ontology segmentation shall intelligent web by also adding further artificial intelligence help to extract only those parts of a large ontology that are relevant for a certain scenario and to create a stand-alone ontology out of these concepts. Seidenberg and Rector com- pare and evaluate several algorithms for extracting relevant segments in [9]. The key approach is to let the user se- lect some relevant concepts and to automatically add super- classes, subclasses and other related concepts (e.g. classes contained in axioms and restrictions) to the ontology view. We implemented a similar, lightweight online approach as part of the UbisEditor. UbisEditor 3.0 uses the same graphical user interface as the UbisWorld ontology browser, but with additional features 2. THE WEB ONTOLOGY EDITOR enabled like check boxes, a context menu and editable tree The idea behind UbisEditor is the following (see Figure 2): node labels. Our basic ontology is created and edited by an ontology expert, who can use either a common ontology editor like Protégé or UbisEditor to perform this task. Our ontology community, on the other hand, extends the basic ontology via UbisEditor with the possible issue of dublicated and con- flicting concepts. Another feature of UbisEditor is to allow an individual ontology user to create a personalized ontology segment. Figure 3: Part of the UbisEarth ontology tree 2.1 Architecture of UbisEditor 3.0 Figure 4 shows the basic architecture of the UbisEditor 3.0 Figure 2: Collaborative Ontology Engineering in the and the ontology browser. Both the developers of our group Web 3.0 era with UbisEditor and our user community can use the UbisEditor to manip- ulate the different ontologies. When committing changes, The UbisEditor 3.0 itself is part of the UbisWorld project, a script stores the appropriate data in the database and a which focuses its research on ubiquitous user modeling [1] script for building the ontology trees sends the updated in- and Web 3.0. The latest tool set version UbisWorld 3.0 inte- formation back to the client. With this technology, we are grates Web 2.0-like services and Semantic Web technologies. able to overcome the performance issues that appeared in The knowledge base of the system is built out of two on- the context of web ontology editors so far. tologies: GUMO (General User Modeling Ontology) [2] and UbisOntology. These ontologies are represented as foldable trees whose nodes consist of classes and instances whereby the conversion from ontologies usually represented as graphs to ontology trees is performed by using multiple heritage. In addition, several external ontologies (e.g. SUMO, DOLCE, OpenCyc) and taxonomies (e.g. the Amazon.com category tree) have been parsed and integrated into the UbisWorld. At the moment, further OWL ontologies can only be im- ported by our team, but we plan to provide a functionality to allow users to import and edit their own ontologies any- time soon. All the trees can be browsed in a very efficient way by using Ajax technologies [5]. This means that the data needed to display the layer of a tree is sent to the client not before the user has opened the corresponding parent node. Using this visualization technique we are basically able to display arbitrary large trees. In the UbisEarth ontology tree (our largest ontology with about 28 million nodes), depicted in Figure 3, we are already able to display roles and properties as tree nodes, too. This very useful feature shall also be implemented for the rest of the UbisWorld. Furthermore, this tree emphasizes the strength of our visualization by displaying limitation nodes, which subsume large numbers of nodes in ten thousand or hundred packets, respectively. These nodes add additional structure to the tree hierarchy and facilitate an easy-to-use Figure 4: Abstract architecture of the UbisEditor tree browsing. 3.0 and visualization system 2.2 Editing Process and Quality Control label according to a situation-aware strategy. The UbisEditor 3.0 already supports the most important In order to make a multilingual labeling of the concepts of functionalities for editing an ontology: creating new classes the different ontologies possible, we provide an additional or instances, renaming and deleting objects as well as chang- method to edit the UbisLabel of an object. When selecting ing a node’s parent via drag&drop. By using a context a node of an ontology tree, a grid appears on the right hand menu, we provide an efficient and easy to use way of perform- side of the UbisWorld webpage (Fig. 6). This grid has two ing these editor actions. Right mouse button click opens the columns (Language and Label) where the different labels context menu and highlights the selected node in the tree that already exist for this concept are shown together with (Fig. 5). This context menu is adaptive to the rights of the corresponding language. Further translations of the con- the user, which depend on the user’s role. This means that cept’s name can be added by first selecting a language out of only users belonging to a certain role can delete objects, for a combo box containing the different iso 639 language codes example. and entering the appropriate name into a text editor field afterwards. This feature facilitates a collective generation of multilingual ontology concepts. Figure 5: The Context Menu Before Inserting a New Figure 6: Grid for Multilingual Label Editing Class When the editing process is finished, the user has to push 2.4 Aspects of Collaborative Ontology Devel- a button to commit those changes to the server. Then a opment script executes the actions corresponding to the type of the The idea to facilitate a collaborative ontology editing raises changes. By changing only those values in the database that several issues. One important task is the implementation of really have changed, the updated tree can be reloaded and a transaction management to avoid problems when multiple displayed immediately to the user. users edit the ontologies and commit their changes simul- For each editing process performed with UbisEditor we store taneously. However, since our system stores the different the identifier of the registered user who is responsible for the ontologies in a database back end, the concurrency control appropriate changes. By doing so, we are able to find out will probably be solved on the database level. In addition, whether a user constantly inserts low quality content. In we think about implementing a locking mechanism on the addition, UbisWorld already has a five-star rating system subtree or ontology module level to avoid inconsistencies. available, with which our user community can help to en- When different members of a community collectively extend sure the quality and integrity of our content [8]. A possible an ontology, different opinions inevitably can cause conflicts extension could be to make it possible to rate the raters, to occur. Consequently, a conflicts resolution is an essen- too. tial functionality. We plan to solve this problem using a combined approach consisting of a community-based and a 2.3 Multilingual Editing of Labels role-based conflicts resolution strategy similar to the one UbisLabel is our approach to define multilingual labels in proposed by Li et al. in [4]. identifiers for semantic web and ubiquitous computing. We In order to avoid dublicated concepts, we already imple- use UbisLabels to denote concepts in our ontologies. The mented a search engine for the UbisWorld system, which basic idea is to use only ASCII characters in names, even if can be used to find classes, instances and properties of the selected special characters are allowed. The syntax of the UbisOntology. This is a very important feature with regard UbisLabel approach is described below. to the editing process using UbisEditor. When a user plans to insert a new element into the UbisWorld ontology, but is [D] UbisLabel ::= SimpleLabel | LanguageLabel | MultiLabel not sure whether an appropriate concept already exists, the [D] SimpleLabel ::= UbisToken UbisSearch can be used to remove ambiguity. [D] LanguageLabel ::= (LanguageCode)+ ".." UbisToken [D] MultiLabel ::= UbisLabel ("..." UbisLabel)+ In the near future we plan to develop a change management [D] [D] LanguageCode ::= ISO_639_1 | "ME" ISO_639_1 ::= "EN" | "DE" | "IT" | "JP" | "YI" | ... system for UbisEditor and to extend the rating system such that performed ontology editing operations can be rated. By doing so, the change history and versioning information of So this approach not only enables multiple labels for any each ontology concept can be displayed on the right side of concept from the knowledge representation point of view, the website helping the user to understand the evolution of but also allows the adaptive selection and presentation of a the ontology. Our user community can help do discuss and decide whether performed changes to the ontology should be gumo revisited for future web 2.0 extensions. In kept or reverted. In this context, the availability of tagging P. Bouquet, J. Euzenat, C. Ghidini, D. L. and annotation facilities as supported by Collaborative Pro- McGuinness, L. Serafini, P. Shvaiko, and H. Wache, tégé [10] becomes essential. The UbisWorld already provides editors, C&O:RR, volume 298 of CEUR Workshop a simple tagging functionality, but more advanced features Proceedings. CEUR-WS.org, 2007. for annotating and discussing ontology concepts and changes [3] A. Kalyanpur, B. Parsia, E. Sirin, B. C. Grau, and are needed. J. Hendler. Swoop: A web ontology editing browser. Web Semantics: Science, Services and Agents on the 2.5 Personalized Ontology Views World Wide Web, 4(2):144–153, June 2006. Another important feature supported by UbisEditor 3.0 is [4] M. Li, D. Wang, X. Du, and S. Wang. Ontology the possibility to create ontology views, i.e. to extract only construction for semantic web: A role-based those parts of the ontology that are relevant for the scenario collaborative development method. pages 609–619. on hand. In editor-mode, the ontology trees are displayed 2005. with a check box on the left-hand side of each node. So the [5] M. Loskyll. Ontological and Ajax-based Extension of user can easily select the needed concepts and create a per- UbisWorld. Bachelor thesis, 2007. Chair for Artifical sonalized ontology view by pushing the appropriate button. Intelligence, Prof. Dr. Dr. h.c. mult. Wahlster, Then an OWL-file is provided for download. Saarland University. We always integrate the direct and indirect superclasses of [6] N. F. Noy, A. Chugh, and H. Alani. The ckc challenge: the selected concepts traversing the hierarchy tree upwards Exploring tools for collaborative knowledge until the top node of the ontology. In addition, we let the construction. Intelligent Systems, 23(1):64–68, 2008. user decide whether only the selected concepts (and the ap- [7] N. F. Noy, M. Crubezy, R. W. Fergerson, propriate superclasses) shall be included in the ontology H. Knublauch, S. W. Tu, J. Vendetti, and M. A. view or also their subclasses. At the moment, the Ubis- Musen. Protégé-2000: an open-source World does not provide functionalities to define and display ontology-development and knowledge-acquisition ontological restrictions and axioms. Consequently, we do environment. AMIA ... Annual Symposium proceedings not consider classes contained in these definitions for the / AMIA Symposium. AMIA Symposium, 2003. creation of ontology segments so far. However, we plan to [8] P. Recktenwald. A Web 2.0 Rating System for do so in the near future. UbisWorld. Bachelor thesis, 2007. Chair for Artifical Intelligence, Prof. Dr. Dr. h.c. mult. Wahlster, 3. CONCLUSIONS AND FUTURE WORK Saarland University. We have presented UbisEditor 3.0, a Web tool which pro- [9] J. Seidenberg and A. Rector. Web Ontology vides lightweight functionalities for efficient collaborative Segmentation: Analysis, Classification and Use, 2006. ontology editing and the generation of personalized ontology [10] T. Tudorache, N. Noy, S. Tu, and M. Musen. views. Besides, our tool can be used to collectively generate Supporting collaborative ontology development in multilingual ontology concepts. The central idea of our ap- protégé. pages 17–32. 2008. proach is to facilitate the distributed extension of our basic [11] T. Tudorache, J. Vendetti, and N. F. Noy. ontologies, that were created by experts, performed by our Web-protege: A lightweight owl ontology editor for ontology community. the web. In C. Dolbear, A. Ruttenberg, and UbisEditor 3.0 is part of the UbisWorld 3.0 tool set that can U. Sattler, editors, OWLED, volume 432 of CEUR be tested online at www.ubisworld.org. Our initial research Workshop Proceedings. CEUR-WS.org, 2008. results are currently transferred to the domain of distributed [12] W. Wahlster and A. Dengel. Web 3.0: Convergence of technology enhanced learning in the EU project GRAPPLE. Web 2.0 and the Semantic Web. Telekom Technology In the near future, we plan to extend the functionality of Radar II, Juni, pages 1–23, 2006. UbisEditor 3.0 in order to support the definition of ontolog- ical axioms, the creation of properties and the user-driven merging of ontologies. Concerning the support of collabo- rative ontology development, mechanisms for concurrency control, conflicts resolution and change management are es- sential. Additionally, we are going to perform an extensive evaluation of the editor features and of our ontology visual- ization techniques. Acknowledgments This work has partly been supported by the EU funded FP7 project GRAPPLE (215434). Special thanks to Francesca Carmagnola. 4. REFERENCES [1] D. Heckmann. Ubiquitous User Modeling. Berlin: Akademische Verlagsgesellschaft Aka GmbH, 2006. [2] D. Heckmann, E. Schwarzkopf, J. Mori, D. Dengler, and A. Kröner. The user model and context ontology