457 research outputs found
Evaluation a of a layered approach to question answering over linked data
No full textWalter S, Unger C, Cimiano P, Bär D. Evaluation a of a layered approach to question answering over linked data. Presented at the The 11th International Semantic Web Conference (ISWC 2012), Boston, USA.We present a question answering system architecture which processes natural language questions in a pipeline consisting of five steps: i) question parsing and query template generation, ii) lookup in an inverted index, iii) string similarity computation, iv) lookup in a lexical database in order to find synonyms, and v) semantic similarity computation. These steps are ordered with respect to their computational effort, following the idea of layered processing: questions are passed on along the pipeline only if they cannot be answered on the basis of earlier processing steps, thereby invoking computationally expensive operations only for complex queries that require them. In this paper we present an evaluation of the system on the dataset provided by the 2nd Open Challenge on Question Answering over Linked Data (QALD-2). The main, novel contribution is a systematic empirical investigation of the impact of the single processing components on the overall performance of question answering over linked data
Automatic Acquisition of Adjective Lexicalizations of Restriction Classes: a Machine Learning Approach
No full textWalter S, Unger C, Cimiano P. Automatic Acquisition of Adjective Lexicalizations of Restriction Classes: a Machine Learning Approach. Journal on Data Semantics. 2016;6(3):113-123
Speeding Up Multilingual Grammar Development by Exploiting Linked Data to Generate Pre-terminal Rules
No full textWalter S, Unger C, Cimiano P. Speeding Up Multilingual Grammar Development by Exploiting Linked Data to Generate Pre-terminal Rules. In: Natural Language Processing and Information Systems. Lecture Notes in Computer Science. Vol 8455. Springer; 2014: 242-245
Vitalistic information systems in the South African public health system : a transactional analysis perspective
No full textIncludes bibliographical references
A corpus-based approach for the induction of ontology lexica
No full textWalter S, Unger C, Cimiano P. A corpus-based approach for the induction of ontology lexica. Presented at the 18th International Conference on Application of Natural Language to Information Systems (NLDB 2013).While there are many large knowledge bases (e.g. Freebase, Yago, DBpedia) as well as linked data sets available on the web, they typically lack lexical information stating how the properties and classes are realized lexically. If at all, typically only one label is attached to these properties, thus lacking any deeper syntactic information, e.g. about syntactic arguments and how these map to the semantic arguments of the property as well as about possible lexical variants or paraphrases. While there are lexicon models such as \emph{lemon} allowing to define a lexicon for a given ontology, the cost involved in creating and maintaining such lexica is substantial, requiring a high manual effort. Towards lowering this effort, in this paper we present a semi-automatic approach that exploits a corpus to find occurrences in which a given property is expressed, and generalizing over these occurrences by extracting dependency paths that can be used as a basis to create lemon lexicon entries. We evaluate the resulting automatically generated lexica with respect to DBpedia as dataset and Wikipedia as corresponding corpus, both in an automatic mode, by comparing to a manually created lexicon, and in a semi-automatic mode in which a lexicon engineer inspected the results of the corpus-based approach, adding them to the existing lexicon if appropriate
Exploiting ontology lexica for generating natural language texts from RDF data
No full textCimiano P, Lüker J, Nagel D, Unger C. Exploiting ontology lexica for generating natural language texts from RDF data. Presented at the 14th European Workshop on Natural Language Generation (ENLG 2013) at ACL
Multilingual question answering over linked data (QALD-3): Lab overview
No full textCimiano P, Lopez V, Unger C, Cabrio E, Ngomo A-CN, Walter S. Multilingual question answering over linked data (QALD-3): Lab overview. In: Information Access Evaluation. Multilinguality, Multimodality, and Visualization. Lecture Notes in Computer Science. Vol 8138. Springer; 2013: 321-332
A lemon lexicon for DBpedia
No full textUnger C, McCrae J, Walter S, Winter S, Cimiano P. A lemon lexicon for DBpedia. In: Sebastian H, Agata F, Caroline B, Pablo M, Dimitris K, eds. Proceedings of 1st International Workshop on NLP and DBpedia, co-located with the 12th International Semantic Web Conference (ISWC 2013), October 21-25, Sydney, Australia. NLP & DBpedia 2013. CEUR Workshop Proceedings; 2013
On-line load balancing made simple: Greedy strikes back
No full textWe provide a new approach to the on-line load balancing problem in the case of restricted assignment of temporary weighted tasks. The approach is very general and allows us to derive on-line algorithms whose competitive ratio is characterized by some combinatorial properties of the underlying graph G representing the problem: in particular, the approach consists in applying the greedy algorithm to a suitably constructed subgraph of G. In the paper, we prove the NP-hardness of the problem of computing an optimal or even a c-approximate subgraph, for some constant c > 1. Nevertheless, we show that, for several interesting problems, we can easily compute a subgraph yielding an optimal on-line algorithm. As an example, the effectiveness of this approach is shown by the hierarchical server model introduced by Bar-Noy et al. (2001). In this case, our method yields simpler algorithms whose competitive ratio is at least as good as the existing ones. Moreover, the algorithm analysis turns out to be simpler. Finally, we give a sufficient condition for obtaining, in the general case, O (sqrt(n))-competitive algorithms with our technique: this condition holds in the case of several problems for which a Ω (sqrt(n)) lower bound is known. © 2006 Elsevier B.V. All rights reserved
Online load balancing made simple: Greedy strikes back
No full textWe provide a new simpler approach to the on-line load balancing problem in the case of restricted assignment of temporary weighted tasks. The approach is very general and allows to derive on-line distributed algorithms whose competitive ratio is characterized by some combinatorial properties of the underlying graph representing the problem. The effectiveness of our approach is shown by the hierarchical server model introduced by Bar-Noy et al '99. In this case, our method yields simpler and distributed algorithms whose competitive ratio is at least as good as the existing ones. Moreover, the resulting algorithms and their analysis turn out to be simpler. Finally, in all cases the algorithms are optimal up to a constant factor. Some of our results are obtained via a combinatorial characterization of those graphs for which our technique yields O(rootn)-competitive algorithms
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