From Hopfield nets to recursive networks to graph machines: numerical machine learning for structured data

  • Authors:
  • Aurélie Goulon-Sigwalt-Abram;Arthur Duprat;Gérard Dreyfus

  • Affiliations:
  • Laboratoire d'Électronique, ESPCI-Paristech, Paris, France;Laboratoire de Chimie Organique, ESPCI-Paristech, Paris, France;Laboratoire d'Électronique, ESPCI-Paristech, Paris, France

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2005

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Abstract

The present paper is a short survey of the development of numerical learning from structured data, an old problem that was first addressed by the end of the years 1980, and has recently undergone exciting developments, both from a theoretical point of view and for applications. Traditionally, numerical machine learning deals with unstructured data, in the form of vectors: neural networks, graphical models, support vector machines, handle vectors of features that are assumed to be relevant for solving the problem at hand (classification or regression). It is often the case, however, that data is structured, i.e. is in the form of graphs; three examples will be described here: prediction of the properties of molecules, image analysis, and natural language processing. The traditional approach consists in handcrafting a vector representation of the structured data (features describing the molecules, "bag of words" for language processing), and subsequently training a machine to perform the task from that representation. By contrast, we describe here a family of approaches (RAAMs, LRAAMs, recursive or folding networks, graph machines) that are specifically designed to learn from structured data. We show that, despite the apparent diversity, two basic principles underlie the recent approaches: first, use structured machines to learn structured data; second, learn representations instead of handcrafting them; although neither principle is really new, they proved very successful for handling structured data, to the point of generating a novel branch of numerical machine learning.