1 Intr oduction
Semantic wikis extend the idea of collaborative content editing (made popular by
systems such as Wikipedia) to the realm of semantically-enriched representations and
formal knowledge models. While a conventional wiki includes structured text and
untyped hyperlinks, a semantic wiki is based on the representation of metadata
elements. Semantic MediaWiki (SMW) [
Despite their potential value as collaborative knowledge editing systems, semantic
wikis often present a number of usability issues for human end users. This is due, at
least in part, to the complexity of the knowledge representation formalisms associated
with languages such as OWL. How can we enable users to create and edit structured
knowledge content (in the form of RDF models and OWL ontologies) without
reneging on the kind of simple user interaction mechanisms that makes conventional
wiki systems, such as Wikipedia, so popular? One answer to this question is to
capitalize on the availability of controlled natural languages (CNLs) that provide
support for ontology model development. CNLs such as Rabbit [
In this paper, we present our efforts to develop a CNL interface for semantic wikis using the Rabbit CNL. Our main contributions are: 1) An extensible platform for CNL interface for semantic wikis with potential to support multiple CNLs; 2) An OWL meta model for knowledge representation on semantic wiki; 3) A prototype implementation for form-based ontology authoring and controlled natural language generation in Rabbit English.
Due to space limitation, complete features of the system are given in a technical
report [
high portability and accessability that many desktop-based tools lack. In particular, the semantic wiki-based approach allows both formal and informal descriptions of knowledge, thus may cover more life cycle phases of knowledge engineering. Finally, as the key components of our system (CNL verbalizers, the OWL meta model, and form-based editor) are themselves stored as wiki pages, the system is highly transparent and easier to extend.
We have implemented a prototype semantic wiki system based on the system architecture presented in Figure 1 (see http://tw.rpi.edu/proj/cnl/). The system enables users to create and edit knowledge models using a form-based interface and it renders semantic content as embedded CNL statements using the Rabbit CNL.
In order to accommodate CNLs, such as Rabbit, within a semantic wiki system, we need to address a number of expressivity constraints associated with conventional semantic wiki systems, such as SMW. SMW does not provide full support for OWL modeling formalisms, and this introduces a mismatch between the kind of knowledge statements that can be represented in Rabbit and the kind of knowledge statements that can be created in SMW.
In order to address this limitation, we developed a meta-model extension to SMW, called SMW-mOWL. SMW-mOWL represents an OWL ontology using a set of ‘semantic templates1’, each of which encodes information about a particular type of ontology element (i.e. classes, properties and individuals). The Template:Class template thus encodes information about OWL classes, while the Template:Property and Template:Individual templates encode information about OWL properties and OWL individuals, respectively. Each of the various axioms and expressions associated with an ontology element (such as a class) is also represented as an instance of a specific semantic template. Thus, the template Template:Some represents the owl:somesValuesFrom restriction, while the template Template:ClassRelation can be used to represent the rdfs:subclassOf axiom. The motivation behind this meta-modeling approach is based on a number of design considerations. These include the following: • Cor r espondence to the OWL Abstr act Syntax (OWL-AS): SMW-mOWL is intended to have a direct correspondence to OWL-AS. Ontology elements, axioms and class expressions in SMW-mOWL are all represented as corresponding wiki templates. For example, the class:
Class(Rabbit partial Animal restriction(eats someValuesFrom(FreshVegetable))) is represented in the semantic wiki as a page using the Template:Class, Template:ClassRelation and Template:Some templates. This results in the following meta-model representation of the aforementioned class:
{{Class|label=Rabbit|plural=Rabbits}} 1 A semantic template extends the usual wiki template with the ability to turn wiki script into semantic annotations with a predefined skeleton, or to control look-and-feel of pages that use the template. • • {{ClassRelation|type=subClassOf|class=Animal}} {{Some|on property=eats|on class=FreshVegetable}} This correspondence between OWL-AS and SMW-mOWL has a couple of advantages. Firstly, OWL-AS can be used as an intermediate syntax for knowledge exchange between SMW and other tools. Secondly, it provides an extensible framework for supporting multiple CNLs within the SMW environment.
UI Cor r espondences: The design of SMW-mOWL is intended to have a direct correspondence to the SMW knowledge editing system. By utilizing what are called ‘semantic forms’ within SMW, each template can be edited using a formbased interface. Having an OWL meta-model thus provides us with a low-cost solution to the problem of implementing a full OWL ontology editor within the SMW environment.
Quer y Convenience: The use of a template-based mechanism for SMW-mOWL allows us to store the OWL ontology in the SMW database and to use SMW-QL (the query language for SMW) to retrieve information from the model.
At the present time, the meta-modeling approach described above provides a significant fragment of representational support for OWL. The form-based interface, however, does impose limits on what kinds of expression a user can create within the system. The user cannot create class expressions of arbitrary complexity, for example, class expressions where the value of a quantifier restriction is itself a complex expression rather than a named class. The following class cannot therefore be created within the semantic wiki system using the form-based interface:
Class(Rabbit partial Animal restriction(eats someValuesFrom(intersectionOf(Vegetable restriction(isFresh value(true))))))
Our future work on the form-based interface, as well as the CNL interface (see section 2), will aim to address this shortcoming.
This paper summarizes our initial efforts to develop a generic CNL interface for semantic wiki systems. Thus far we have specified a system architecture to support the collaborative editing of community knowledge using semantic wikis. We have also developed a set of meta-model extensions to SMW in order to accommodate the expressivity features of OWL-compliant CNLs, like Rabbit. Finally, we have implemented a prototype system (see http://tw.rpi.edu/proj/cnl/) that combines a form-based editor with a CNL generation capability. This system enables users to create/edit ontologies within the SMW environment and to view the contents of those ontologies as embedded CNL (i.e. CNL statements embedded within a semantic wiki page).
Future work will focus on the development of enhanced editing and parsing capabilities. For example, we are currently working on a better user interface to support the direct entry of Rabbit sentences. We also aim to extend the semantic template system in order to accommodate multiple CNLs (e.g. Rabbit, SOS, ACE, etc.) within a single semantic wiki system. This integrative approach to CNLmediated knowledge content creation will, we suggest, surmount some of the usability issues associated with semantic wiki systems and make large-scale collaborative knowledge modeling on the Semantic Web more accessible to a variety of user communities.