LibSwb: Browsing the Entity Context?

Abstract

In this paper we are presenting ongoing work on a software library for on-the- y browsing of Semantic Web content that forms the informational context around an entity. This library is targeted to be integrated into user applications, to extend their range of functionalities in an easy-to-handle and unobtrusive way. We illustrate an application, give details on the implementation of a rst prototype, and evaluate its feasibility.

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The important fact to note is that the data displayed in the entity context is automatically retrieved and joined on-the- y. To a certain extent, approaches to the Semantic Web browsing topic are available. For example Piggy Bank [ 3 ] collects semantic data from web pages and allows users to make annotations and share them among each other. Haystack [ 6 ] is a standalone Semantic Web browser application collecting semantically annotated information from URLs and present it in a generic, content independent interface. Potluck [ 4 ] produces data mash-ups on the basis of di erent URLs provided by the user. Tabulator [ 8 ] is a well-known Semantic Web browser displaying RDF and allowing the user to follow hypertext links, if they point to another RDF document. All approaches mainly rely on URLs to information sources, thus either on a single source or a list of sources. LibSwb instead automatically retrieves information about an entity by querying for okkam identi ers in distributed data sources. Therefore it provides a richer set of information, and additionally is not as error-prone as relying on direct dereferencing of an URL.

Solution Approach

The idea behind our work is to enable Semantic Web browsing, replicating the behavior of a WWW browser hiding the complexity of the ongoing operations. Semantic Web browsing should consist in moving through the \Giant Global Graph" [ 1 ] by presenting a bounded view (a contextual subgraph) focusing on one pivot entity at each browsing step.

A brief description of the operations necessary to realize such a browsing process is presented in the following. (1) De ne starting pivot URI ; (2) Retrieve pivot URI alternatives ; (3) Retrieve information about the pivot URI by inquiring data sources as Sindice [ 9 ] looking for RDF documents including the pivot URI and its alternatives; (4) Building a partial RDF graph by merging and pruning the retrieved RDF documents.

We implemented a prototype of LibSwb aiming to de ne \proof of concept", enabling the execution of some experiments. This implementation relies on the Jena framework, combined with standard graph manipulation algorithms for RDF graph management, and the Sindice index for RDF document retrieval.

In this very early state of development, we can only provide a rough approximation about runtime behavior. LibSwb has been tested by browsing the entity context of the authors' FOAF-pro les using the authors' okkam URIs to retrieve information. Three steps of browsing have been performed as scenario involving 11 documents with 62kB and 310 RDF statements. By running this test scenario on a Pentium 4 computer (3Ghz, 3GB RAM) an average runtime of 6847ms was determined, where the machine was occupied 6827ms for downloading the RDF les, which leaves a total of 20ms for computations, i.e. in average 6.6ms per browsing step.

The results reveal that the most time expensive activity in realizing on-they entity-centric browsing is downloading of RDF les. Hence, we will focus on reducing download time on the one hand and use more sophisticated and complex algorithms for merging and pruning to improve results on the other hand. 3

Conclusion

As previously stated, the work described in this article is in an early stage of development. While improving performance, e.g. by parallelizing processes and avoiding le reloading through caching, we are also going to extend LibSwb in the direction of contextual representation and management 1, to lay the foundations for several context-related aspects, including the limitations of graph merging, provenance and quality of data, as well as contextual visual representation of information. The next evolution will not rely on Sindice alone, but provide a pluggable architecture for information sources like Falcon [ 5 ], Microformats2 1 Context-sensitivity of RDF data has been addressed on several levels, we refer the reader to [ 7 ] and the contained Related Work section. 2 http://microformats.org/ and emering sources. Additionally, we will consider references to further RDF data embedded in documents. In this way, we are moving towards the vision of the W3C Semantic Web research group about RDF browsing3.

This highly exible architecture will make LibSwb easily usable within many kinds of applications that require a convenient interface to Semantic Web content, such as authoring systems that need to provide up-to-date background information about entities, or extensions to web browsers that add a navigational layer on top of document hyperlink structures. Our declared goal is to ease the development of entity-centric (Semantic) Web enabled applications and extend the functional range of networked applications. We are thus planning to make the library publicly available as soon as the most important features mentioned in the previous section are implemented and su ciently stable.

References

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[8] Tim Berners-Lee , Yuhsin Chen , Lydia Chilton, Dan Connolly, Ruth Dhanaraj, James Hollenbach, Adam Lerer, and David Sheets. Tabulator: Exploring and analyzing linked data on the semantic web . In Proceeding The 3rd International Semantic Web User Interaction Workshop November 6 , 2006 Athens, Georgia, USA, 2006 .

[9] Giovanni Tummarello , Renaud Delbru, and Eyal Oren . Sindice.com: Weaving the open linked data . In Proceedings of the 7th International Semantic Web Conference 2007 (ISWC'07) , Busan, Korea, 2007 .

3 i.e. Tabulator RDF Browser (http://www .w3.org/2005/ajar/tab)