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
contains certain edges. Checking sequence generation is thus represented in terms of the rural Chinese postman problem. The checking sequence is produced by starting
. 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
represents a transition test for a transition
that ends at the initial state
. We replace
by the corresponding sequence
of edges from
to form a tour
denote a walk produced by starting
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.
• H. Ural is with the School of Information Technology and Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada.
E-mail: firstname.lastname@example.org, email@example.com.
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: firstname.lastname@example.org, and reference IEEECS Log Number TC-0432-1106.
Digital Object Identifier no. 10.1109/TC.2008.173.