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Learning Concept Lengths Accelerates Concept Learning in ALC

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Part of the Lecture Notes in Computer Science book series (LNCS,volume 13261)


Concept learning approaches based on refinement operators explore partially ordered solution spaces to compute concepts, which are used as binary classification models for individuals. However, the number of concepts explored by these approaches can grow to the millions for complex learning problems. This often leads to impractical runtimes. We propose to alleviate this problem by predicting the length of target concepts before the exploration of the solution space. By these means, we can prune the search space during concept learning. To achieve this goal, we compare four neural architectures and evaluate them on four benchmarks. Our evaluation results suggest that recurrent neural network architectures perform best at concept length prediction with a macro F-measure ranging from 38% to 92%. We then extend the CELOE algorithm, which learns ALC concepts, with our concept length predictor. Our extension yields the algorithm CLIP. In our experiments, CLIP is at least 7.5\(\times \) faster than other state-of-the-art concept learning algorithms for ALC—including CELOE—and achieves significant improvements in the F-measure of the concepts learned on 3 out of 4 datasets. For reproducibility, we provide our implementation in the public GitHub repository at


  • Concept learning
  • Concept length
  • Structured machine learning
  • Description logic
  • Learning from examples
  • Prediction of concept lengths

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  • DOI: 10.1007/978-3-031-06981-9_14
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Fig. 1.
Fig. 2.


  1. 1.

    Also called class expression learning (CEL) [13]. See Sect. 2 for a formal definition.

  2. 2.

    The implementations of OCEL and ELTL in the DL-Learner framework, which we used for our experiments, fail to consider the set threshold accurately. Hence, Table 7 contains values larger than 2 min for these two algorithms.

  3. 3.

    Note that we ran OCEL with its default settings and F1 scores are not available.


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This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860801. This work has been supported by the German Federal Ministry of Education and Research (BMBF) within the project DAIKIRI under the grant no 01IS19085B and by the German Federal Ministry for Economic Affairs and Climate Action (BMWK) within the project RAKI under the grant no 01MD19012B. The authors gratefully acknowledge the funding of this project by computing time provided by the Paderborn Center for Parallel Computing (PC2).

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Kouagou, N.J., Heindorf, S., Demir, C., Ngomo, AC.N. (2022). Learning Concept Lengths Accelerates Concept Learning in ALC. In: , et al. The Semantic Web. ESWC 2022. Lecture Notes in Computer Science, vol 13261. Springer, Cham.

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