Ontologies continuously become larger and more complex, and therefore more and more di cult to maintain, to edit and to develop by one single person or a small group of experts. The basic principle of Web 2.0, on the other hand, is to use the willingness and knowledge of a huge community of users to create rich user-generated content. The obvious idea that comes to mind is to combine the technologies of the Semantic Web with the trend of the Web 2.0. We present UbisEditor 3.0, an easy-to-use web tool for the creation and manipulation of structured collective knowledge represented as ontologies. This web ontology editor is realized as part of the UbisWorld project and already supports ontology editing techniques like adding new concepts, renaming and deleting, but also the creation of personalized ontology views.
The characterization of Web 3.0 used in this paper is based
on [
With the increasing importance of ontologies, several
ontology editors have been developed. Two of the currently
most popular ones are Protege [
The idea behind UbisEditor is the following (see Figure 2):
Our basic ontology is created and edited by an ontology
expert, who can use either a common ontology editor like
Protege 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
conicting concepts. Another feature of UbisEditor is to allow
an individual ontology user to create a personalized ontology
segment.
The UbisEditor 3.0 itself is part of the UbisWorld project,
which focuses its research on ubiquitous user modeling [
All the trees can be browsed in a very e cient way by using
Ajax technologies [
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 tree browsing.
UbisEditor 3.0 uses the same graphical user interface as the UbisWorld ontology browser, but with additional features enabled like check boxes, a context menu and editable tree node labels.
Figure 4 shows the basic architecture of the UbisEditor 3.0 and the ontology browser. Both the developers of our group and our user community can use the UbisEditor to manipulate the di erent ontologies. When committing changes, a script stores the appropriate data in the database and a script for building the ontology trees sends the updated information back to the client. With this technology, we are able to overcome the performance issues that appeared in the context of web ontology editors so far.
The UbisEditor 3.0 already supports the most important functionalities for editing an ontology: creating new classes or instances, renaming and deleting objects as well as changing a node's parent via drag&drop. By using a context menu, we provide an e cient and easy to use way of performing these editor actions. Right mouse button click opens the context menu and highlights the selected node in the tree (Fig. 5). This context menu is adaptive to the rights of the user, which depend on the user's role. This means that only users belonging to a certain role can delete objects, for example. label according to a situation-aware strategy.
In order to make a multilingual labeling of the concepts of the di erent ontologies possible, we provide an additional method to edit the UbisLabel of an object. When selecting a node of an ontology tree, a grid appears on the right hand side of the UbisWorld webpage (Fig. 6). This grid has two columns (Language and Label) where the di erent labels that already exist for this concept are shown together with the corresponding language. Further translations of the concept's name can be added by rst selecting a language out of a combo box containing the di erent iso 639 language codes and entering the appropriate name into a text editor eld afterwards. This feature facilitates a collective generation of multilingual ontology concepts. When the editing process is nished, the user has to push a button to commit those changes to the server. Then a script executes the actions corresponding to the type of the changes. By changing only those values in the database that really have changed, the updated tree can be reloaded and displayed immediately to the user.
For each editing process performed with UbisEditor we store
the identi er of the registered user who is responsible for the
appropriate changes. By doing so, we are able to nd out
whether a user constantly inserts low quality content. In
addition, UbisWorld already has a ve-star rating system
available, with which our user community can help to
ensure the quality and integrity of our content [
UbisLabel is our approach to de ne multilingual labels in identi ers for semantic web and ubiquitous computing. We use UbisLabels to denote concepts in our ontologies. The basic idea is to use only ASCII characters in names, even if selected special characters are allowed. The syntax of the UbisLabel approach is described below. [D] UbisLabel ::= SimpleLabel | LanguageLabel | MultiLabel [D] SimpleLabel ::= UbisToken [D] LanguageLabel ::= (LanguageCode)+ ".." UbisToken [D] MultiLabel ::= UbisLabel ("..." UbisLabel)+ [D] LanguageCode ::= ISO_639_1 | "ME" [D] ISO_639_1 ::= "EN" | "DE" | "IT" | "JP" | "YI" | ...
So this approach not only enables multiple labels for any concept from the knowledge representation point of view, but also allows the adaptive selection and presentation of a
The idea to facilitate a collaborative ontology editing raises
several issues. One important task is the implementation of
a transaction management to avoid problems when multiple
users edit the ontologies and commit their changes
simultaneously. However, since our system stores the di erent
ontologies in a database back end, the concurrency control
will probably be solved on the database level. In addition,
we think about implementing a locking mechanism on the
subtree or ontology module level to avoid inconsistencies.
When di erent members of a community collectively extend
an ontology, di erent opinions inevitably can cause con icts
to occur. Consequently, a con icts resolution is an
essential functionality. We plan to solve this problem using a
combined approach consisting of a community-based and a
role-based con icts resolution strategy similar to the one
proposed by Li et al. in [
In order to avoid dublicated concepts, we already implemented a search engine for the UbisWorld system, which can be used to nd classes, instances and properties of the UbisOntology. This is a very important feature with regard to the editing process using UbisEditor. When a user plans to insert a new element into the UbisWorld ontology, but is not sure whether an appropriate concept already exists, the UbisSearch can be used to remove ambiguity.
In the near future we plan to develop a change management
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
each ontology concept can be displayed on the right side of
the website helping the user to understand the evolution of
the ontology. Our user community can help do discuss and
decide whether performed changes to the ontology should be
kept or reverted. In this context, the availability of tagging
and annotation facilities as supported by Collaborative
Protege [
Another important feature supported by UbisEditor 3.0 is the possibility to create ontology views, i.e. to extract only those parts of the ontology that are relevant for the scenario on hand. In editor-mode, the ontology trees are displayed with a check box on the left-hand side of each node. So the user can easily select the needed concepts and create a personalized ontology view by pushing the appropriate button. Then an OWL- le is provided for download.
We always integrate the direct and indirect superclasses of the selected concepts traversing the hierarchy tree upwards until the top node of the ontology. In addition, we let the user decide whether only the selected concepts (and the appropriate superclasses) shall be included in the ontology view or also their subclasses. At the moment, the UbisWorld does not provide functionalities to de ne and display ontological restrictions and axioms. Consequently, we do not consider classes contained in these de nitions for the creation of ontology segments so far. However, we plan to do so in the near future.
We have presented UbisEditor 3.0, a Web tool which provides lightweight functionalities for e cient collaborative ontology editing and the generation of personalized ontology views. Besides, our tool can be used to collectively generate multilingual ontology concepts. The central idea of our approach is to facilitate the distributed extension of our basic ontologies, that were created by experts, performed by our ontology community.
UbisEditor 3.0 is part of the UbisWorld 3.0 tool set that can be tested online at www.ubisworld.org. Our initial research results are currently transferred to the domain of distributed technology enhanced learning in the EU project GRAPPLE. In the near future, we plan to extend the functionality of UbisEditor 3.0 in order to support the de nition of ontological axioms, the creation of properties and the user-driven merging of ontologies. Concerning the support of collaborative ontology development, mechanisms for concurrency control, con icts resolution and change management are essential. Additionally, we are going to perform an extensive evaluation of the editor features and of our ontology visualization techniques.
This work has partly been supported by the EU funded FP7 project GRAPPLE (215434).
Special thanks to Francesca Carmagnola.