On-Line algorithms, real time, the virtue of laziness, and the power of clairvoyance

  • Authors:

  • Giorgio Ausiello;Luca Allulli;Vincenzo Bonifaci;Luigi Laura

  • Affiliations:

  • Department of Computer and Systems Science, University of Rome, “La Sapienza”, Roma, Italy;Department of Computer and Systems Science, University of Rome, “La Sapienza”, Roma, Italy;Department of Computer and Systems Science, University of Rome, “La Sapienza”, Roma, Italy;Department of Computer and Systems Science, University of Rome, “La Sapienza”, Roma, Italy

  • Venue:
  • TAMC'06 Proceedings of the Third international conference on Theory and Applications of Models of Computation
  • Year:
  • 2006

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Abstract

In several practical circumstances we have to solve a problem whose instance is not a priori completely known. Situations of this kind occur in computer systems and networks management, in financial decision making, in robotics etc. Problems that have to be solved without a complete knowledge of the instance are called on−lineproblems. The analysis of properties of on-line problems and the design of algorithmic techniques for their solution (on−linealgorithms) have been the subject of intense study since the 70-ies, when classical algorithms for scheduling tasks in an on-line fashion [22] and for handling paging in virtual storage systems [11] have been first devised. In the 80-ies formal concepts for analyzing and measuring the quality of on-line algorithms have been introduced [40] and the notion of competitiveanalysis has been defined as the ratio between the value of the solution that is obtained by an on-line algorithm and the value of the best solution that can be achieved by an optimum off-line algorithm that has full knowledge of the problem instance. Since then a very broad variety of on-line problems have been addressed in the literature [14, 19]: memory allocation and paging, bin packing, load balancing in multiprocessor systems, updating and searching a data structure (e.g. a list), scheduling, financial investment, etc.