Markus Stocker

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In this paper, we formalize the problem of Basic Graph Pattern (BGP) optimization for SPARQL queries and main memory graph implementations of RDF data. We define and analyze the characteristics of heuristics for selectivity-based static BGP optimization. The heuristics range from simple triple pattern variable counting to more sophisticated selectivity(More)
This research explores three SPARQL-based techniques to solve Semantic Web tasks that often require similarity measures, such as semantic data integration, ontology mapping, and Semantic Web service matchmaking. Our aim is to see how far it is possible to integrate customized similarity functions (CSF) into SPARQL to achieve good results for these tasks.(More)
In this paper, we present PelletSpatial, a qualitative spatial reasoning engine implemented on top of Pellet. PelletSpatial provides consistency checking and query answering over spatial data represented with the Region Connection Calculus (RCC). It supports all RCC-8 relations as well as standard RDF/OWL semantic relations, both represented in RDF/OWL. As(More)
We present Owlgres, a DL-Lite reasoner implementation written for PostgreSQL, a mature open source database. Owlgres is an OWL reasoner that provides consistency checking and conjunctive query services, supports DL-LiteR as well as the OWL sameAs construct, and is not limited to PostgreSQL. We discuss the implementation with special focus on sameAs and the(More)
The vision of semantic business processes is to enable the integration and inter-operability of business processes across organizational boundaries. Since different organizations model their processes differently, the discovery and retrieval of similar semantic business processes is necessary in order to foster inter-organizational collaborations. This(More)
Query engines for ontological data based on graph models mostly execute user queries without considering any optimization. Especially for large ontologies, optimization techniques are required to ensure that query results are delivered within reasonable time. OptARQ is a first prototype for SPARQL query optimization based on the concept of triple pattern(More)
This poster describes three static SPARQL optimization approaches for in-memory RDF graphs: (1) a selectivity estimation index (SEI) for single query triple patterns; (2) a query pattern index (QPI) for joined triple patterns; and (3) a hybrid optimization approach that combines both indexes. Using the Lehigh University Benchmark (LUBM), we show that the(More)
In environmental engineering, sensor measurement is a process undertaken with respect to an environmental domain, i.e. an area of interest, to measure a domain property. Knowledge of a domain, meaning its concepts and relations that hold among them, can be formally represented by means of ontology. Therefore, given an ontology for an environmental domain,(More)
Information systems that build on sensor networks often process data produced by measuring physical properties. These data can serve in the acquisition of knowledge for real-world situations that are of interest to information services and, ultimately, to people. Such systems face a common challenge, namely the considerable gap between the data produced by(More)
A recurrent problem in applications that build on environmental sensor networks is that of sensor data organization and interpretation. Organization focuses on, for instance, resolving the syntactic and semantic heterogeneity of sensor data. The distinguishing factor between organization and interpretation is the abstraction from sensor data with(More)