Learning Qualitative Models of Dynamic Systems

  • Authors:
  • David T. Hau;Enrico W. Coiera

  • Affiliations:
  • School of Medicine, The Johns Hopkins University, Baltimore, MD 21205, USA/ E-mail: dave@welchlink.welch.jhu.edu;Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS12 6QZ, UK/ E-mail: ewc@hplb.hpl.hp.com

  • Venue:
  • Machine Learning - special issue on inductive logic programming
  • Year:
  • 1997

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Abstract

The automated construction of dynamic system modelsis an important application area for ILP. We describe amethod that learns qualitative models from time-varying physiologicalsignals. The goal is to understand the complexity of thelearning task when faced with numerical data, what signal processing techniques are required, and how this affects learning. The qualitative representation is based on Kuipers‘ QSIM. Thelearning algorithm for model construction is based on Coiera‘s GENMODEL. We show that QSIM models are efficiently PAClearnable from positive examples only, and that GENMODEL is anILP algorithm for efficiently constructing a QSIM model. We describe bothGENMOEL which performs RLGG on qualitative states to learn aQSIM model, and the front-end processing and segmenting stagesthat transform a signal into a set of qualitative states.Next we describe results of experiments on data from six cardiac bypass patients. Useful models wereobtained, representing both normal and abnormal physiologicalstates. Model variation across time and across different levels oftemporal abstraction and fault tolerance is explored.The assumption made by many previous workers that the abstraction of examples from data can be separated from the learning task is not supported by this study. Firstly, the effects ofnoise in the numerical data manifest themselvesin the qualitative examples. Secondly, the models learned aredirectly dependent on the initial qualitative abstraction chosen.