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{{{Challenges}}} +
RDF stats + VoID +
For the following sample queries, real-wor …
For the following sample queries, real-world data of sunspot observations recorded at
Kanzelh¨ohe Solar Observatory (KSO) have been used. The observatory is also a partner
in the Austrian Grid project.
The queries are shown in Fig. 2. Query 1 retrieves the first name, the last name,
and optionally the e-mail address of scientists who have done observations. Query 2
retrieves all observations ever recorded by Mr. Otruba.
observations ever recorded by Mr. Otruba. +
Performance +
Evaluate the system using a set of sample queries +
The tests were performed with the followin …
The tests were performed with the following setup: the mediator (and also the test client) where running on a 2.16 GHz Intel Core 2 Duo with 2 GB memory and a 2 MBit link to the remote endpoints. All endpoints were simulated on the same physical host running two AMD Opteron CPUs at 1.6 GHz and 2 GB memory.
D Opteron CPUs at 1.6 GHz and 2 GB memory. +
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Because ARQ is using a pipelining concept the response time is very good, even
when data has to be retrieved from a remote data source. +
1 +
In this contribution a system is presented …
In this contribution a system is presented, which provides access to distributed data sources using Semantic Web technology. While it was primarily designed for data sharing and scientific collaboration, it is regarded as a base technology useful for many other Semantic Web applications. The proposed system allows to retrieve data using SPARQL queries, data sources can register and abandon freely, and all RDF Schema or OWL vocabularies can be used to describe their data, as long as they are accessible on the Web. Data heterogeneity is addressed by RDF-wrappers like D2R-Server placed on top of local information systems. A query does not directly refer to actual endpoints, instead it contains graph patterns adhering to a virtual data set. A mediator finally pulls and joins RDF data from different endpoints providing a transparent on-the-fly view to the end-user. The SPARQL protocol has been defined to enable systematic data access to remote endpoints. However, remote SPARQL queries require the explicit notion of endpoint URIs. The presented system allows users to execute queries without the need to specify target endpoints. Additionally, it is possible to execute join and union operations across different remote endpoints. The optimization of such distributed operations is a key factor concerning the performance of the overall system. Therefore, proven concepts from database research can be applied.
pts from database research can be applied. +
Querying Distributed RDF Data Sources +
In this contribution a mediator-based syst …
In this contribution a mediator-based system for virtual data integration based on SemanticWeb technology has been presented. The system is primarily developed for sharing scientific data, but because of its generic architecture, it is supposed to be used for many other Semantic Web applications. In this paper query federation based on SPARQL and Jena/ARQ has been demonstrated in detail and several concepts for query optimization which is currently on the agenda have been discussed. Additional contributions can be expected after the implementation of additional features mentioned before.
n of additional features mentioned before. +
Other future work will be the support for …
Other future work will be the support for DESCRIBE-queries and IRIs as subjects. In
future, the mediator should also use an OWL-DL reasoner to infer additional types for
subject nodes specified in the query pattern. Currently, types have to be explicitly specified
for each BGP (more precisely for the first occurrence: the algorithm caches already
known types). OWL-DL constraints like for example a qualified cardinality restriction
on obs:byObserver with owl:allValuesFrom obs:Observer would allow
the mediator to deduce types of other nodes in the query pattern.
types of other nodes in the query pattern. +
not available. +
{{{Motivation}}} +
Jena +
Open source +
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Jena +
{{{Methodology}}} +
Creation date
"Creation date" is a predefined property that corresponds to the date of the first revision of a subject and is provided by Semantic MediaWiki.
09:53:11, 26 March 2018 +
Has processing error
"Has processing error" is a predefined property provided by Semantic MediaWiki and represents errors that appeared in connection with improper value annotations or input processing.
Last editor is
"Last editor is" is a predefined property that contains the page name of the user who created the last revision and is provided by Semantic MediaWiki.
Modification date
"Modification date" is a predefined property that corresponds to the date of the last modification of a subject and is provided by Semantic MediaWiki.
19:52:56, 11 July 2018 +
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