Archive for » February, 2009 «

Wednesday, February 25th, 2009 | Author:

Clarisse Kagoyire today defended her MSc thesis at the International Institute for Geo-Information Science and Earth Observation (ITC) in Enschede. She explored the application of XML database technology for distributed spatial data processing using web services. The idea is that XML database technology, if equipped with spatial support, can avoid development and run-time overhead by working directly on exchanged GML data compared to typical relational SDI*-based solutions as it allows you to stay in the XML-domain. Clarisse implemented a soil erosion scenario involving 5 independent XML database servers using MonetDB/XQuery as XML database platform. MonetDB/XQuery’s support for XRPC proved important and powerful for realizing the distributed query processing. Furthermore, Clarisse used and helped specify the recently implemented XQuery spatial functionality. The research shows that XML database technology is suitable for implementing web services and that the preliminary unoptimized spatial support in MonetDB/XQuery is already sufficient for certain distributed spatial data processing tasks.
(*) SDI = Spatial Data Infrastructure

Tuesday, February 17th, 2009 | Author:

Last week (11 – 13 February) we held a Pathfinder project meeting. 20 people attended from 6 institutes (Uni.Tübingen, CWI, Uni.Twente, NFI Den Haag, Uni.Konstanz, ETH Zürich). We discussed about scalability, multiple front- and backends, full-text support, porting to MonetDB5, etc. Regarding the latter, we decided to indeed invest in porting Pathfinder to MonetDB5 starting in April. There were also a number of presentations. I presented the first attempts in adding spatial support to Pathfinder and Riham presented our ROX run-time join optimization approach for XQuery.

Friday, February 06th, 2009 | Author:

The project description for Tjitze Rienstra’s Msc project has been finalized. The project is being supervised by me and Paul van der Vet.

Dealing with uncertainty in the Semantic Web
The notion of data integration is essential to the Semantic Web. Its real advantage is that it enables us to gather data from different sources, reason over this data and get results that may otherwise not have been easy to find.
However, data integration can lead to conflicts. Different sources may provide contradicting information about the same real world objects. The result is uncertainty. The technologies of the Semantic Web are assertional, which means that they cannot deal with uncertainty very well.

The essential standards (RDF, RDFS, OWL, SPARQL) will be extended in order to deal with uncertainty. We will first make clear what is required in terms of expressiveness. We then specify an extension by formalizing a ‘possible world’ semantics for RDF. It will be necessary to consider what the consequences are for RDFS and OWL. Finally, querying with SPARQL must be adapted to work with this possible world model, while at the same time be computationally efficient. Validation will be done by testing a prototype against a movie database, containing conflicting data from different sources.