• James Abello

Congratulations to Prof. Abello and his co-authors for receiving the European Symposia on Algorithms (ESA) Test-of-Time Award 2017 for the following paper:

James Abello, Adam L. Buchsbaum, and Jeffery R. Westbrook
A Functional Approach to External Graph Algorithms
Proceedings ESA'98, pp. 332-343, also in: Algorithmica 32 (2002) 437-458

The ESA Test-of-Time Award (ToTA) recognizes excellent papers in algorithms research that were published in the ESA proceedings 19-21 years ago and which are still influential and stimulating for the field today. For the 2017 award, papers from ESA'96 to ESA'98 were considered. The award committee selected the paper for the ESA ToTA 2017. The paper stands out as a classic in the algorithms field and continues to be cited as an exemplary study in its field.

The paper deals with the design of algorithms that operate on massive data sets in external memory. Building on the well-known I/O model of complexity by Aggarwal and Vitter, the authors introduce a novel design principle for external algorithms based purely on functional transformations of the data, which facilitates standard checkpointing and program optimization techniques. Illustrated on a variety of graph problems, their approach is proved to be elegant and versatile in the design of both deterministic and randomized external algorithms while the resulting I/O complexities remain competitive. Functional algorithms are also designed for semi-external problems, in which the nodes fit in main memory but the connecting edges are abundant and only available in external memory. The paper is an excellent illustration of how general principles of functional program design and model-based complexity can remain in harmony in the field of external algorithms.

Award Committee: Giuseppe F. Italiano (Rome), Mike Paterson (Warwick), Jan van Leeuwen (Utrecht)