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The publication of freely available and machine-readable information has increased significantly in the last years. Especially the Linked Data initiative has been receiving a lot of attention. Linked Data is based on the Resource Description Framework (RDF) and anybody can simply publish their data in RDF and link it to other datasets. The structure is similar to the World Wide Web where individual HTML documents are connected with links. Linked Data entities are identified by URIs which are dereferenceable to retrieve information describing the entity. Additionally, so called SPARQL endpoints can be used to access the data with an algebraic query language (SPARQL) similar to SQL. By integrating multiple SPARQL endpoints it is possible to create a federation of distributed RDF data sources which acts like one big data store.
In contrast to the federation of classical relational database systems there are some differences for federated RDF data. RDF stores are accessed either via SPARQL endpoints or by resolving URIs. There is no coordination between RDF data sources and machine-readable meta data about a source- data is commonly limited or not available at all. Moreover, there is no common directory which can be used to discover RDF data sources or ask for sources which offer specific data. The federation of distributed and linked RDF data sources has to deal with various challenges. In order to distribute queries automatically, suitable data sources have to be selected based on query details and information that is available about the data sources. Furthermore, the minimization of query execution time requires optimization techniques that take into account the execution cost for query operators and the network communication overhead for contacting individual data sources. In this thesis, solutions for these problems are discussed. Moreover, SPLENDID is presented, a new federation infrastructure for distributed RDF data sources which uses optimization techniques based on statistical information.
Im Rahmen dieser Arbeit soll eine Methodik erarbeitet werden, die englische, keyword-basierte Anfragen in SPARQL übersetzt und bewertet. Aus allen generierten SPARQL-Queries sollen die relevantesten ermittelt und ein Favorit bestimmt werden. Das Ergebnis soll in einer Nutzerevaluation bewertet werden.
Einfluss eines Ausrichtungswerkzeugs auf die Bedienbarkeit in unbeaufsichtigten Eyetrackingsystemen
(2015)
Eye gaze trackers are devices that can estimate the direction of gaze of a person. Among usability testing eye tracking also allows persons with decreased limb mobility to control or to interact with the computer. The quality and availability of eye tracking equipment has been increasing while costs have been decreasing. This development leads to entering new markets by using eye tracking as an additional input dimension for a variety of applications. Up to now eye tracking has been supervised by qualified experts, who assured that the important conditions like position in front of the eye tracking device, calibration and light conditions has been kept, while using.
This thesis examines an adjustment tool, which is helping the user to adjust in front of the eye tracker and helping to keep this position during the experiment. Furthermore the accuracy while moving the head has been analysed. In this experiment an remote eye gaze tracker has been used to control a game character in the video game called 'Schau Genau!'. The goal was to determine whether the game is playable without the barrier of adjusting and calibration. The results show that adjusting in front of an eye tracker is not a problem, keeping this position is. Small changes of the head position after the calibration process leads to a lack of accuracy. Giving up the calibration and using someone else calibration shows way bigger deviation. Additional head movement increases error rate and makes controlling more difficult.