
FEBRUARY 2009 (Vol. 58, No. 2) pp. 287287
00189340/09/$31.00 © 2009 IEEE
Published by the IEEE Computer Society
Published by the IEEE Computer Society
Correction to "Reduced Length Checking Sequences"
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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.
Email: rob.hierons@brunel.ac.uk.
• H. Ural is with the School of Information Technology and Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada.
Email: 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 email to: tc@computer.org, and reference IEEECS Log Number TC04321106.
Digital Object Identifier no. 10.1109/TC.2008.173.
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