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Clustered graph visualization techniques are an easy to understand way of hiding complex parts of a visualized graph when they are not needed by the user. When visualizing RDF, there are several situations where such clusters are defined in a very natural way. Using this techniques, we can give the user optional access to some detailed information without unnecessarily occupying space in the basic...
The state of the art in semi-structured data processing (and XML in particular) and Semantic Web repositories correspond to each other: the non-scalability of pilot implementations, the inability of optimizations, and the cost of the fully native implementation. Although there are successful implementations in each of the approaches, none of the methods may be considered universal. The Bobox framework...
Graph visualization is one of the popular ways to present RDF data. But all practical RDF visualizers have to somehow deal with the problem of the size of the data. Not only can the total number of triples in RDF data be very large, but even degrees of the nodes of the graph can be very high. This article discusses some problems and solution related to visualization and exploration of such data, usually...
One family of visualization tools for the semantic Web are those that directly display the underlying RDF data. Most of them use the inherent graph structure of RDF data and present the user with some drawing of the graph. While it is usually sufficient to give the user with decent understanding of data, there are some features of RDF that could be used to improve the visualization, for instance the...
One way to see the semantic Web is to think of it as a set of all-knowing technologies that respond to whatever the user asks. The other view is that it is a set of standards and tools that help build better Web applications. Since the latter is probably more realistic at the moment, it means that a lot of software has to be developed before we start actually seeing the semantic Web in widespread...
There have been many attempts to create software that would allow the users to design SQL queries visually, even though it is not very natural to handle relations and relational algebra (the theoretical background of SQL) this way. But the RDF data format is based on directed labeled graphs, whose visual representation is very natural. We have created an RDF visualizer and tried to extend it to support...
There are already several tools available that are capable of visualizing RDF data. The problem with RDF data is that they tend to be very large. To handle the data, the visualizers cannot display the whole data but rather need to use some kind of navigation. We have designed and implemented such visualizer. This paper describes our approach to the navigation, which was designed specifically with...
The two basic problems of graph drawing - drawing of nodes and drawing of edges - are often handled by one algorithm that finds suitable positions for both nodes and edges. However, there are situations where positions of nodes are fixed, for instance if they were defined by the user or the exact position of the nodes is somehow significant. In these cases we need an algorithm that draws only the...
The semantic Web is not widespread as it has been expected by its founders. This is partially caused by lack of standard and working infrastructure for the semantic Web. We have built a working, portable, stable, high-performance infrastructure for the semantic Web. This enables various experiments with the semantic Web in the real world.
Since many XML documents do not contain any schema definition, we expected that there will be also RDF documents without RDF schema or ontology. Then the data can only be viewed as a general labeled directed graph and the idea to present the data to the user by drawing the graph seems natural. Because the data can be extremely large, it is impossible to display the whole graph at one time. Only a...
The semantic Web is not widespread as it has been expected by its founders. This is partially caused by lack of standard and working infrastructure for the semantic Web. We have built a working, portable, stable, high-performance infrastructure for the semantic Web. This paper is focused on tasks performed by the infrastructure.
Software testing efforts account for a large part of software development costs. However, as educators, we struggle to properly prepare students to perform software testing activities. This struggle is caused by multiple factors: (1) it is challenging to effectively incorporate software testing into an already over-packed curriculum, (2) ad-hoc efforts to teach testing generally happen too late in...
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