Issue No. 02 - February (2009 vol. 58)

ISSN: 0018-9340

pp: 287

DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/TC.2008.173

R. M. Hierons , Brunel University, Uxbridge, Middlesex

H. Ural , University of Ottawa, Ottawa

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 sequenceThe corrected algorithm of [

^{1}] returns the checking sequenceof 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.

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