OntoWiki: A Tool for Social, Semantic Collaboration

We present OntoWiki, a tool providing support for agile, distributed knowledge engineering scenarios. OntoWiki facilitates the visual presentation of a knowledge base as an information map, with different views on instance data. It enables intuitive authoring of semantic content, with an inline editing mode for editing RDF content, similar to WYSIWYG for text documents. It fosters social collaboration aspects by keeping track of changes, allowing to comment and discuss every single part of a knowledge base, enabling to rate and measure the popularity of content and honoring the activity of users. Ontowiki enhances the browsing and retrieval by offering semantic enhanced search strategies. All these techniques are applied with the ultimate goal of decreasing the entrance barrier for projects and domain experts to collaborate using semantic technologies. In the spirit of the Web 2.0 OntoWiki implements an ”architecture of participation” that allows users to add value to the application as they use it. It is available as open-source software and a demonstration platform can be accessed at http://3ba.se. We present a tool supporting agile Knowledge Engineering in a pure Web environment. It is called OntoWiki since it is close in the spirit to existing Wiki systems. Technologically however, the OntoWiki design is independent and complementary to conventional Wiki technologies. As such, the OntoWiki approach differs from recently emerged strategies to integrate Wiki systems and the Semantic Web (cf. [6,5,8,11,12]). In these works it is proposed to integrate RDF triples into Wiki texts in a special syntax. It is a straightforward combination of existing Wiki systems and the Semantic Web knowledge representation paradigms. However, we see the following obstacles: – Usability: The main advantage of Wiki systems is their unbeatable usability. Adding more and more syntactic possibilities counteracts ease of use for editors. – Redundancy: To allow the answering of real-time queries to the knowledge base statements have to be stored additionally in a triple store. This introduces a redundancy complicating the implementation. – Scalability: Knowledge base changes which involve statements with different subjects will scale very bad since all corresponding Wiki texts have to be parsed and changed. The OntoWiki strategy presented in this paper, on the contrary, does not try to mix text editing with knowledge engineering, instead it applies the Wiki paradigm of “making it easy to correct mistakes, rather than making it hard to make them”[9] to collaborative knowledge engineering. The main goal of the OntoWiki approach thus is to rapidly simplify the presentation and acquisition of instance data from and for end users. This is achieved by regarding knowledge bases as ”information maps”. Each node at the information map is represented visually and intuitively for end users in a generic but configurable way and interlinked to related digital resources. Users are further enabled to enhance the knowledge schema incrementally as well as to contribute instance data agreeing on it as easy as possible to provide more detailed descriptions and modelings. Consequently, the following requirements have been determined for OntoWiki: – Intuitive display and editing of instance data should be provided in generic ways, yet enabling means for domains specific views. – Semantic views allow the generation of different views and aggregations of the knowledge base. – Versioning and Evolution provides the opportunity to track, review and selectively roll-back changes. – Semantic search facilitates easy-to-use full-text searches on all literal data, search results can be filtered and sorted (using semantic relations). – Community support enables discussions about small information chunks. Users are encouraged to vote about distinct facts or prospective changes. – Online statistics interactively measures the popularity of content and activity of users. – Semantic syndication supports the distribution of information and their integration into desktop applications. In the remainder of the paper we propose strategies on how to put these requirements into effect in a real-life system and report about implementation in a prototypical OntoWiki on the basis of Powl [1], a framework for Semantic Web application development. To stress the generic character of OntoWiki, the figures in this paper show screenshots of the OntoWiki prototype with a knowledge base collaboratively developed and containing information about scientific conferences, as well as another publicly available knowledge base containing information about research projects, people and publications at a research institute. 3 at http://3ba.se 4 http://www.aifb.uni-karlsruhe.de/viewAIFB OWL.owl 1 Visual Representation of Semantic Content The compromise of, on the one hand, providing a generic user interface for arbitrary RDF knowledge bases and, on the other hand, aiming at being as intuitive as possible is tackled by regarding knowledge bases as ”information maps”. Each node at the information map, i.e. RDF resource, is represented as a Web accessible page and interlinked to related digital resources. These Web pages representing nodes in the information map are divided into three parts: a left sidebar, a main content section and a right sidebar. The left sidebar offers the selection of content to display in the main content section. Selection opportunities include the set of available knowledge bases, a class hierarchy browser and a full-text search. Once a selection is made, the main content section will arrange matching content in a list view linking to individual views for individual instances (cf. 1). The right sidebar offers tools and complementary information specific to the selected content. Figure 1. List view (left) and view of an individual instance with expanded inline reference view (right). List views allow to view a selection of several instances in a combined view. The selection of instances to display can be either based on class membership or on the result of a selection by facet or full-text search. OntoWiki identifies those properties used in conjunction with the instances of the selection. The display of the corresponding property values for each instance can be switched on, thus resulting in a tabular view. Furthermore, each individual instance displayed is linked to an individual view of that instance. Individual views combine all the properties attached to an particular instance. Property values pointing to other individuals are rendered as HTML links to the corresponding individual view. Alternatively, to get information about the referenced individual without having to load the complete individual view it is possible to expand a short summary (loaded per AJAX) right where the reference is shown. The right sidebar provides additionally information about similar instances (of the same type) and incoming links (i.e. references from other instances). Different Views on Instance Data The OntoWiki prototype facilitates different views on instance data. Such views can be either domain specific or generic. Domain specific views have to be implemented as plug-ins. Generic views provide visual representations of instance data according to certain property values. The following views are currently implemented: Figure 2. Map view (left) and calendar view (right) of instance data. Map View. If the selected data (either a single instance or a list of instances) contains property values representing geographical information (i.e. longitude and latitude coordinates) a map view provides information about the geographical location of the selected data (cf. Figure 2). Technically, this view is realized by integrating the Google Maps API. However, the integration is bi-directional, since objects displayed in the map can be expanded and instance details are dynamically fetched from the knowledge base and displayed directly within the map view. The selection of instances to be displayed can be furthermore the result of a facet-based filtering (cf. Section 4). Calendar View. Instances having property values with the associated datatype xsd:date can be displayed in a calendar view (cf. Figure 2). As for the map view the selection of instances displayed in the calendar view can be the result of a facet-based filtering. Each item displayed is linked to the individual view of 5 http://www.google.com/apis/maps/ the corresponding instance. The sidebar offers a link to export calendar items in iCal format, which enables to import the selected calendar items into a desktop calender application. 2 Collaborative Authoring To enable users to edit information presented by the OntoWiki system as intuitively as possible, the OntoWiki approach supports two complementary edit strategies for the knowledge base: – Inline editing, the smallest possible information chunks (i.e. statements) presented in the OntoWiki user interface are editable for users. – View editing, common combinations of information (such as an instance of a distinct class) are editable in one single step. Both editing strategies are supported by a mixed client and server side concept identification and reuse technology and a library of generic editing widgets. In the remainder of this section the editing strategies and their supporting technologies are presented in more detail.