Browsing Linked Data with Fenfire
Tuukka Hastrup

Richard Cyganiak

Uldis Bojārs

University of Jyväskylä
Jyväskylä, Finland

Digital Enterprise ResearchInstituteNational University of Ireland,
GalwayDigital Enterprise ResearchInstituteNational University of Ireland,
Galwayrichard.cyganiak@deri.org

uldis.bojars@deri.org

Tuukka.Hastrup@iki.fi

ABSTRACT
A wealth of information has recently become available asbrowsable RDF data on the Web, but the selection of client
applications to interact with this Linked Data remains limited. We show how to browse Linked Data with Fenfire,a Free and Open Source Software RDF browser and editor
that employs a graph view and focuses on an engaging andinteractive browsing experience. This sets Fenfire apart fromprevious table- and outline-based Linked Data browsers.

1.

INTRODUCTION

Linked Data [1] is Semantic Web data that emphasises thegraph of relations between resources while recognising thatthe data comes from Semantic Web documents that need tobe retrievable using standard conventions. Domain-specificapplications can crawl Linked Data to pull together and display information from various sources. However, there is aneed for generic Linked Data browsers as well, as they help
data producers to check what they publish and data consumers to check what is available.
One generic Linked Data browser is Tabulator [2], but it
does not provide a graph view. Karger and schraefel provide insights on why graph views often are not the best viewsof Semantic Web data [4], but they acknowledge that graphviews have a high “cool factor” and a niche. We considera case that lies in this niche: we want to show the graphdata as directly as possible. We apply a Free and Open
Source Software rich desktop application, Fenfire1 , and its
graph view to Linked Data browsing because unlike otherbrowsers, this is a visually appealing, engaging and interactive demonstration of the Semantic Web’s capabilities. Agraph view is a good way to explore a web of information,and it is close to the nature of Linked Data as a heterogeneous, web-like environment with little high-level structure.
In the following, we demonstrate how the Fenfire applica1

http://fenfire.org/

Copyright is held by the author/owner(s).
LDOW2008, April 22, 2008, Beijing, China.

tion provides a useful Linked Data browsing experience, go
through an example, describe the implementation and conclude with some future directions.

2.

BROWSING EXPERIENCEThe Fenfire application is a generic RDF browser and editor
with features useful for Linked Data browsing. The userinterface employs the conventional graph representation ofthe RDF data model. To make the visualisations scalable
in the number of nodes in the graph and to focus on one
thing at a time, only one central node and its surroundings
are displayed concurrently. It is possible to switch between
two views implemented based on the concept: a simple listview of objects associated with the focused subject (say, acontainer), and the generic graph view from Fentwine [3].
A browsing session starts from some URI which is retrieved
for a document with RDF data. This URI will be the initial focus unless the document has a foaf:primaryTopic
defined, in which case the primary topic URI will be chosen
as the initial focus.
For the surroundings, the generic graph view shows to theleft of the focus all triples that have the focus as an object,
and to the right all triples that have the focus as a subject.
Each triple is shown as a predicate connecting the subject
to the object. This view is applied recursively to each displayed node until, with distance, the graph fades away to thebackground. If the node has an rdfs:label, it is displayed
instead of the URI.
Graph navigation can be done entirely via keyboard by rotating the surrounding nodes around the centre and moving
focus to the node immediately to the left or right of the centre. While there is limited space for the surrounding nodes,
all nodes can be navigated to via the rotation.
To enable browsing of Linked Data, Fenfire dereferences theURI of the focused node and retrieves any rdfs:seeAlso
related to this node whenever instructed to do so. For example, in Figure 1 a user has loaded the FOAF profile ofone person, followed a foaf:knows link to another person
and retrieved the FOAF profile of this person.
As an important alleviation of incompletely linked data,
Fenfire adds triples asserting that the graph retrieved contains information about all of its disconnected components.

Figure 1: Starting from Tim Berners-Lee, a user has followed FOAF data to a document about Henry Story.

3.

USE CASES

We target two audiences primarily:• Semantic Web researchers, application developers anddata producers need to explore available data on thelevel of individual triples. Fenfire provides a convenient alternative to manually downloading graph documents, reading the serialisation formats, and trying
to match URIs to discover the links in the data.
• People who want to learn about or demonstrate theSemantic Web and what data is available benefit froma visual presentation that truthfully shows the networked nature of the data. Here it is highly advantageous that Linked Data documents that follow theguidelines include an rdfs:label for each node.

Some Linked Data browsers can edit the data as well. Fenfire
can edit RDF graphs, but we need to implement remotepublishing interfaces in addition to the current feature ofsaving to local files.
Information display and navigation can be enhanced if there
is knowledge about the user interaction requirements for a
specific domain. Thus, Fenfire should have some automatic
ontology-awareness and more should be configurable withsettings and plug-ins.

6.

7.
4.

IMPLEMENTATION

Fenfire has its origins in ZigZag [6], which is a system for
managing interlinked, distributed data and is completely independent of the World Wide Web standards. Fentwine [3]incorporated Semantic Web standards and became a graphview RDF browser, as did its sibling BuoyOING [5] (BuoyOriented Interface, Next Generation) user interface, whichadds spatial navigation and concentrates on it.
Fenfire is implemented in the Haskell programming language
to achieve high programmer productivity while meeting performance requirements for real-time animation and for browsing large graphs. It uses the Raptor library of the Redland
project for RDF parsing, the GTK library for the standard
graphical user interface elements and the Cairo library forthe animated, vector-graphics based visualisations.
A major part of the architecture is the key-frame and identitybased visualisation and animation system that provides theuser continuous feedback on how the navigation and theswitching between alternative views change what is visible.

5.

CONCLUSIONS

We applied Fenfire to the task of browsing Linked Data witha graph view and highlighted the use cases of exploring,learning about and demonstrating Semantic Web data.

ACKNOWLEDGEMENTS

The implementation of Fenfire in Haskell was initially developed by Benja Fallenstein and Tuukka Hastrup.

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