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Issue No.10 - October (2007 vol.19)
pp: 1448
Published by the IEEE Computer Society
Manolis Koubarakis , IEEE Computer Society
In the above-cited paper, which appeared in the IEEE Transactions on Knowledge and Data Engineering, vol. 19, no. 8, pp. 1116-1130, Aug. 2007, some information appeared incorrectly. We apologize for the error. Please see the list of corrections:

    • On p. 1118 in [ 1], in the paragraph above Definition 1, "follows:." should have been "follows:"

    • On p. 1122, right column, line -16 from the bottom, " $b E\!\!:\!\!B\;a$ " should have been " $b\; E\!\!:\!\!B\;a$ ."

    • On p. 1123, the display equation in Proposition 2 appeared incorrectly.

    Instead of appearing as:

$$\eqalign{&R_{11}^{\leftarrow}\!:\!\cdots\!:\!R_{1k}^{\leftarrow} \circ R_{21}qq^{\leftarrow}\!:\!\cdots\!:\!R_{2m}^{\leftarrow} =\cr& f(N^{\leftarrow}, W^{\leftarrow}, S^{\leftarrow}, E^{\leftarrow}, B) = f(W, S, E, N, B).}$$

    It should have appeared as:

$$\eqalign{&R_{11}^{\leftarrow}\!:\!\cdots\!:\!R_{1k}^{\leftarrow} \circ R_{21}^{\leftarrow}\!:\!\cdots\!:\!R_{2m}^{\leftarrow} =\cr& f(N^{\leftarrow}, W^{\leftarrow}, S^{\leftarrow}, E^{\leftarrow}, B) = f(W, S, E, N, B).}$$

    • On p. 1126, right column, line -7 from the bottom, the following equation:

$$R_{1}\circ R_{2}:\subseteq Combine(R_{11}\circ R_{2}, \ldots, R_{1k}\circ R_{2})$$

    should have appeared as:

$$R_{1}\circ R_{2}\; Combine(R_{11}\circ R_{2}, \ldots, R_{1k}\circ R_{2}).$$

    • On p. 1129, the Acknowledgments section was left out. It should have appeared as shown below:

    Acknowledgments. This work has been partially supported by PENED 03, a project cofunded by the European Social Fund (75 percent) and the General Secretariat of Research and Technology (25 percent).

    S. Skiadopoulos is with the Department of Computer Science and Technology, University of Peloponnese, Karaiskaki Street, 22100, Tripoli, Hellas. E-mail:

    N. Sarkas is with the Department of Computer Science, University of Toronto, 10 King's College Road, M5S 3G4, Toronto, ON, Canada.


    T. Sellis is with the School of Electrical and Computer Engineering, Computer Science Division, National Technical University of Athens, 9, Iroon Polytechneiou Street, GR-15773 Zographou, Athens, Hellas.


    M. Koubarakis is with the Department of Informatics and Telecommunications, National and Kapodistrian University of Athens, Panepistimiopolis, Ilisia, Athens 15784, Greece. E-mail:

For information on obtaining reprints of this article, please send e-mail to:, and reference IEEECS Log Number TKDE-0081-0206.


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