With the growing interest in publishing data according to the Linked Data principles, it becomes more important to provide intuitive tools for users to view and interact with resources. The characteristics of Linked Data pose several challenges for user-friendly presentation of the information. In this work, we present the DBpedia Viewer as one method to address this problem. The DBpedia Viewer is the new DBpedia Linked Data user interface, which makes DBpedia data more accessible to non-experts while integrating the DBpedia service eco system as well as external Linked Data services.
This work describes DBpedia Viewer, the new DBpedia [
additional service which allows to search for DBpedia
entities using either strings or pre xes (for auto-completion).
The DBpedia mappings wiki 4 is an e ort to crowdsource the
mappings between the Wikipedia infoboxes and the
DBpedia ontology. Apart from DBpedia speci c tools, external
vizualization tools have been developed that use DBpedia,
such as RelFinder [
Such tools and services exist independently, but together form an eco system, which provides added value for the DBpedia datasets. Our new interface integrates several tools in a generic manner { partly to increase user-friendliness and partly to showcase the achievements in the Linked Data space obtained so far.
The new DBpedia Linked Data interface (DBpedia Viewer) co-exists with the previous interface which serves Linked Data content to machines and browsers without JavaScript support. While we can default to the new interface when it is supported by the visiting agent, users can easily switch between the two interfaces.
DBpedia Viewer brings several improvements on the presentation of information. In addition to many cosmetic changes, DBpedia Viewer provides improved layout choices and new functionalities that aim to make the UI more useful. The layout has been adapted to provide additional functionality as naturally as possible. As illustrated in Figure 1, several new features are added, each discussed in Section 4.2. DBpedia Viewer is provided as open source on Github5.
The architecture can be divided in three levels. The base level is the triple store, which is accessible using the SPARQL query language. The web server and server-side code are built on top of the database. The third level is the clientside code.
The old interface was implemented with server-side code that generated a very simple HTML/RDFa page. DBpedia Viewer provides two modes: A simple HTML/RDFa view for machines and clients without JavaScript support and a rich web interface for humans based on JavaScript. A switch between the two interfaces is also available. The rich web interface is based solely on client-side code to construct the web page. All SPARQL queries are executed directly from JavaScript which minimizes the page generation time and reduces the load on the web server.
Following, we provide an overview of DBpedia Viewer technology stack (Section 4.1). We elaborate on the interface features (Section 4.2) with an emphasis on the Triple Action Framework (Section 4.3). Finally, we discuss the extensibility of the tool(Section 4.4).
We use the Open Source edition of the Virtuoso server6 as our triple store. Virtuoso has a modular architecture and supports plugins. These plugins use the VSP (Virtuoso Server Pages) language to communicate with the triple store, serve web requests and provide Linked Data. The previous DBpedia interface was built as a Virtuoso plugin and the DBpedia Viewer is built on top of the existing code. Most of the new interface is client-side logic written in JavaScript. As explained above, the client-side code constructs the page by issuing SPARQL queries to the con gured endpoints. Therefore, it is easy to use the new interface for non-Virtuoso deployments by only serving the client-side code. However, in this case, the old server-generated HTML/RDFa interface is not preserved.
For the client-side logic, we used AngularJS 7, an opensource JavaScript framework that implements the Model View Controller (MVC) paradigm for web applications. For styling and layout, we used the CSS from Twitter Bootstrap8.
Following we provide an elaborate discussion of the new DBpedia Viewer features.
The pretty box (part one of Figure 1) displays important properties of the viewed entity. There is a prede ned set of facts we provide, namely: (1) a picture, (2) the title, (3) the types, (4) a short description and (5) links to other resources. These data are generated from the set of triples describing the viewed resources using prede ned mappings. The DBpedia datasets provide most of this general information for all entities. In some cases, however, the picture or links to other resources are not available. The DBpedia Viewer does not perform automatic selection of relevant properties to display. This is out of the scope of this project. Our goal was to develop a UI that is customizable to con gure relevant properties used to adapt the view.
In the top right corner of the pretty box (Figure 1), three icons trigger the entity actions. The currently available actions are links to alternate data representations (XML/RDF, n3, JSON-LD, ...) as well as links to consult the resource using alternative Linked Data browsers.
DBpedia Viewer provides search functionality with autocomplete capabilities by re-using the DBpedia Lookup service. DBpedia Lookup enables searching for DBpedia entities using strings or provides pre x-based suggestions.
The language ltering system allows the user to choose a preferred display language. This lters all literal values based on the user preferences and displays only the relevant values. This feature is helpful on dbpedia.org where labels and
abstracts exist in 12 di erent languages. In the case a literal does not exist in the preferred language, a fallback language (usually English) is chosen by default.
For entities having location information (latitude and longitude), a map is shown with its coordinates. OpenStreetMap is used for the map display.
Part four of Figure 1 highlights the triple ltering feature. Triples can be ltered using both properties and values. This is useful for the users who quickly want to nd speci c properties and values. The ltering is based on string matching and supports all literal values as well as URIs.
The shortcut box (part 5 in Figure 1) provides anchor links to some important properties of entities. However, the list of properties is currently hardcoded and contains links to categories, types, external links, etc...
When the user hovers over a DBpedia link (URI, ontology property or class) a concise, language- ltered preview is displayed. For entities, this preview contains a picture (if available), the title and a short description. Part 6 of Figure 1 shows a preview of the French Gothic architecture entity. 4.2.7
As displayed in part 8 of (Figure 1), next to each triple, different icons exist, each representing a di erent triple action. Triple actions are enabled using conditions on the triple. Thus, the set of available actions for di erent triples may be di erent. When the conditions are met, the action icon is displayed next to the triple. When the user clicks on the triple action icon, the action is executed. Below is an overview of the currently implemented user actions: Annotation { uses DBpedia Spotlight to annotate text. Only applicable to texts of certain length.
RelFinder { links to RelFinder, where the connections (including indirect ones) between the viewed entity and the value entity can be explored. Only applicable to DBpedia resources.
LodLive { opens the value entity with the LodLive browser. Only applicable to DBpedia resources. OpenLink Faceted Browser { view the value entity using OpenLink Faceted Browser. Only applicable to DBpedia resources.
Wikipedia { opens the Wikipedia page associated with the value entity. Only applicable to DBpedia resources. DBpedia template mapping { links to the DBpedia mapping associated with the DBpedia template. Only applicable to DBpedia resources under the Wikipedia template namespace.
The Triple Action Framework (TAF) aims to improve the integration of tools from the DBpedia eco system on the DBpedia website. The interface maintainer can easily add new actions or adapt existing ones for a particular deployment. TAF allows to de ne a triple action with the following core semantics, (1) bind and (2) execute.
Upon page load, for each triple, the bind method of each action is called to determine whether this action is applicable for this triple. The bind method may use any information available from the triple to decide whether the action is applicable or not. For example, the DBpedia Spotlight annotation action should only be made available for annotation of textual resources, so the bind method of this action checks whether the object of the triple is a string literal and whether it exceeds a con gurable minimum length. The execute method of an action is called when the user clicks on an action icon next to the triple. For the DBpedia Spotlight annotation action, this method uses the text in the object of the triple, sends it to the DBpedia Spotlight API for annotation and waits for a response. When the API responds, the Spotlight action changes the display value of the object of the triple to show the annotations.
In the actual implementation, TAF provides additional hooks, providing more functionality to de ne new actions with ease. Moreover, the Triple Action Framework allows to de ne locally/globally stateful actions and hidden (system-level) actions that execute upon binding and are not available to the users. Actions of the hidden type are used to detect coordinates for the map and to populate the shortcut box as well as some parts of the pretty box.
The triple action framework (TAF) promotes the extensibility of the new interface. The website maintainer can quickly de ne new actions and add them to the interface. TAF lightens adding new functionality by providing a useful abstraction where easy access to the triple is provided and displaying is already taken care of. To create a new action, one simply needs to implement the hooks with the desired action logic. We are looking for ways to make TAF action creation easier.
DBpedia is distributed in many language chapters [
RelFinder [
DBpedia Spotlight [
Another tool integrated as a triple action is LodLive [
Dadzie and Rowe [
The Marbles Linked Data browser 9 is a server-side
application that generates HTML from Semantic Web content
using Fresnel [
Pubby 10 is a server-side Java application that can be
congured to use a SPARQL endpoint and publish the data
behind it as Linked Data. It also provides a simple (static)
HTML user interface. The Graphity project 11 provides a
framework for publishing RDF data or building applications
around it. LDIF [
formation about entities from di erent datasets but does not focus on displaying data.
The DBpedia Viewer is a step towards a customizable framework for interactive, user-friendly presentation of Linked Data. The original goal was a DBpedia-speci c user interface that integrates some tools working with DBpedia. However, the Triple Action Framework also proved to be useful for de ning system actions, which allow for greater and easier customization of the interface.
The interface does not try to conceal the technical philosophy behind Linked Data. Instead, it embraces the philosophy and presents the data as it is in a visually appealing fashion, highlighting the underlying ideas and demonstrating the possibilities of the integrated tools.
The Triple Action Framework (TAF) introduced with DBpedia Viewer demonstrates a method for adding interactive functionality to Linked Data, going beyond merely serving RDF facts. Such ideas may not only inspire improvements in other Linked Data interfaces but might also evolve to a standardized framework for human interaction with data across the Semantic Web in the future.
Future versions of DBpedia Viewer will enforce a stronger
modularization between triples, actions and display, thus
following the MVC design pattern. This will generalize the
interface into a framework that can be customized for
different datasets. We also plan to add triple actions for the
incorporation of triple validation by the end users [
We would like to thank Google for sponsoring this work through the Google Summer of Code 2013 project.12 This work was also supported by grants from the European Union's 7th Framework Programme provided for the projects LOD2 (GA no. 257943) and GeoKnow (GA no. 318159).