On Restricted-Focus-of-Attention Learnability of Boolean Functions

  • Authors:
  • Andreas Birkendorf;Eli Dichterman;Jeffrey Jackson;Norbert Klasner;Hans Ulrich Simon

  • Affiliations:
  • Universität Dortmund, Fachbereich Informatik, D-44221 Dortmund, Germany. E-mail: birkendo@lmi.ruhr-uni-bochum.de;Department of Mathematics, London School of Economics, Houghton Street, London WC2A 2AE, UK. And, Department of Computer Science, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK. E ...;Math and Computer Science Department, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, USA. E-mail: jackson@mathcs.duq.edu;Universität Dortmund, Fachbereich Informatik, D-44221 Dortmund, Germany. E-mail: klasner@lmi.ruhr-uni-bochum.de;Universität Dortmund, Fachbereich Informatik, D-44221 Dortmund, Germany. E-mail: simon@lmi.ruhr-uni-bochum.de

  • Venue:
  • Machine Learning - Special issue on the ninth annual conference on computational theory (COLT '96)
  • Year:
  • 1998

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Abstract

In the k-Restricted-Focus-of-Attention (k-RFA) model, only k of the nattributes of each example are revealed to the learner, although the set ofvisible attributes in each example is determined by the learner. While thek-RFA model is a natural extension of the PAC model, there arealso significant differences. For example, it was previously known thatlearnability in this model is not characterized by the VC-dimension and thatmany PAC learning algorithms are not applicable in the k-RFAsetting.In this paper we further explore the relationship between the PAC andk-RFA models, with several interesting results. First, wedevelop an information-theoretic characterization of k-RFAlearnability upon which we build a general tool for proving hardnessresults. We then apply this and other new techniques for studying RFAlearning to two particularly expressive function classes,k-decision-lists (k-DL) and k-TOP,the class of thresholds of parity functions in which each parity functiontakes at most k inputs. Among other results, we prove a hardness result for k-RFA learnability of k-DL,k ≤ n-2. In sharp contrast, an (n-1)-RFAalgorithm for learning (n-1)-DL is presented. Similarly, weprove that 1-DL is learnable if and only if at least half of the inputs arevisible in each instance. In addition, we show that there is auniform-distribution k-RFA learning algorithm for the class ofk-DL. For k-TOP we show weak learnability by ak-RFA algorithm (with efficient time and sample complexity forconstant k) and strong uniform-distribution k-RFAlearnability of k-TOP with efficient sample complexity for constant k. Finally, by combining some of our k-DLand k-TOP results, we show that, unlike the PAC model, weaklearning does not imply strong learning in thek-RFA model.