K-Comma Codes and Their Generalizations

  • Authors:

  • Bo Cui;Lila Kari;Shinnosuke Seki

  • Affiliations:

  • (Correspd.) Department of Computer Science, University of Western Ontario, London, Ontario, Canada, N6A 5B7 bcui2@csd.uwo.ca/ lila@csd.uwo.ca/ sseki@csd.uwo.ca;Department of Computer Science, University of Western Ontario, London, Ontario, Canada, N6A 5B7 bcui2@csd.uwo.ca/ lila@csd.uwo.ca/ sseki@csd.uwo.ca;Department of Computer Science, University of Western Ontario, London, Ontario, Canada, N6A 5B7 bcui2@csd.uwo.ca/ lila@csd.uwo.ca/ sseki@csd.uwo.ca

  • Venue:
  • Fundamenta Informaticae
  • Year:
  • 2011

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Abstract

In this paper, we introduce the notion of k-comma codes - a proper generalization of the notion of comma-free codes. For a given positive integer k, a k-comma code is a set L over an alphabet Σ with the property that LΣ kL ∩ Σ +LΣ + = ∅. Informally, in a k-comma code, no codeword can be a subword of the catenation of two other codewords separated by a “comma” of length k. A k-comma code is indeed a code, that is, any sequence of codewords is uniquely decipherable. We extend this notion to that of k-spacer codes, with commas of length less than or equal to a given k. We obtain several basic properties of k-comma codes and their generalizations, k-comma intercodes, and some relationships between the families of k-comma intercodes and other classical families of codes, such as infix codes and bifix codes. Moreover, we introduce the notion of n-k-comma intercodes, and obtain, for each k ≥ 0, several hierarchical relationships among the families of n-k-comma intercodes, as well as a characterization of the family of 1-k-comma intercodes.