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Issue No.02 - February (2009 vol.58)
pp: 287
R. M. Hierons , Brunel University, Uxbridge, Middlesex
H. Ural , University of Ottawa, Ottawa
ABSTRACT
This paper describes corrections to a previous paper, Reduced Length Checking Sequecnes, that appeared in IEEE Transactions on Computers in 2002 (51 9, pp.1111-1117).
The paper [ 1] describes improvements on the algorithm from [ 2], which produces a checking sequence from a finite state machine that has a known distinguishing sequence . However, while the improvements described in [ 1] are valid, the final step of the checking sequence generation algorithm was not included and we outline this step here.
The algorithm in [ 1] produces a directed graph and then generates a tour of such that contains certain edges. Checking sequence generation is thus represented in terms of the rural Chinese postman problem. The checking sequence is produced by starting at vertex . However, in contrast to [ 2], in doing this we may fail to check the final transition in the tour and, if this is the case, then we need to add a distinguishing sequence to the end of the sequence produced by [ 1]. We can thus produce a checking sequence from in the following way: We choose an edge from such that represents a transition test for a transition that ends at the initial state of . We replace by the corresponding sequence of edges from to form a tour . Let denote a walk produced by starting with and let be the label of . We return the input/output sequence that forms our checking sequence.
Although both [ 1] and [ 2] correctly state that the algorithm of [ 2] should start a tour at the vertex , instead, in the examples, [ 1] started it at . As a result, [ 1] did not apply the algorithm of [ 2] correctly to the example and should have given the checking sequence

The corrected algorithm of [ 1] returns the checking sequence

of length 64 (rather than one of length 61 reported).

R.M. Hierons is with the School of Information Systems, Computing, and Mathematics, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK.

E-mail: rob.hierons@brunel.ac.uk.

H. Ural is with the School of Information Technology and Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada.

E-mail: ural@site.uottawa.ca, ural@sci.uottawa.ca.

Manuscript received 13 Nov. 2006; accepted 23 Jan. 2007; published online 15 Sept. 2008.

Recommended for acceptance by B. Bose.

For information on obtaining reprints of this article, please send e-mail to: tc@computer.org, and reference IEEECS Log Number TC-0432-1106.

Digital Object Identifier no. 10.1109/TC.2008.173.