Optimization techniques play a significant role in improving description logic reasoners covering the Web Ontology Language (OWL). These techniques are essential to speed up these reasoners. Many of the optimization techniques are based on heuristic choices. Optimal heuristic selection makes these techniques more effective. The FaCT++ OWL reasoner and its Java version JFact implement an optimization technique called ToDo list which is a substitute for a traditional top-down approach in tableau-based reasoners. The ToDo list mechanism allows one to arrange the order of applying different rules by giving each a priority. Compared to a top-down approach, the ToDo list technique has a better control over the application of expansion rules. Learning the proper heuristic order for applying rules in ToDo lis will have a great impact on reasoning speed. We use a binary SVM technique to build our learning model. The model can help to choose ontology-specific order sets to speed up OWL reasoning. On average, our learning approach tested with 40 selected ontologies achieves a speedup of two orders of magnitude when compared to the worst rule ordering choice.
Several research efforts have been conducted on learning different factors that have an impact on improving reasoning speed for reasoners. First, @cite_14 applied supervised machine learning to learn the feature behavior for predicting the performance of OWL reasoners. Later, @cite_7 came up with more relevant features for the reasoning performance of ontologies. The results show the hardness of predicting OWL reasoners' performance due to the complexity of ontologies. However, it confirms that considering the correlation of ontologies' features or metrics thereof improves the predictions. Another study investigates the usefulness of different features by categorizing them while expanding the works of the previously mentioned papers @cite_6 .
@cite_14 @cite_6 @cite_7
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A key issue in semantic reasoning is the computational complexity of inference tasks on expressive ontology languages such as OWL DL and OWL 2 DL. Theoretical works have established worst-case complexity results for reasoning tasks for these languages. However, hardness of reasoning about individual ontologies has not been adequately characterised. In this paper, we conduct a systematic study to tackle this problem using machine learning techniques, covering over 350 real-world ontologies and four state-of-the-art, widely-used OWL 2 reasoners. Our main contributions are two-fold. Firstly, we learn various classifiers that accurately predict classification time for an ontology based on its metric values. Secondly, we identify a number of metrics that can be used to effectively predict reasoning performance. Our prediction models have been shown to be highly effective, achieving an accuracy of over 80 . We propose a novel approach for performance prediction of OWL reasoners that selects suitable, small ontology subsets, and then extrapolates reasoner's performance on them to the whole ontology. We investigate intercorrelation of ontology features using PCA and discuss various error measures for performance prediction.