ACM Policy on Prior Publication and Simultaneous Submissions The technical contributions appearing in ACM conference proceedings and journals are normally original papers that have not been previously published in a refereed or formally reviewed publication. Issuing the paper as a technical report, posting the paper on a web site, or presenting the paper at a workshop or conference that does not publish formally reviewed proceedings does not disqualify it from appearing in an ACM publication. Workshops and conferences are encouraged to indicate in their calls for papers whether or not they will publish formally reviewed proceedings so that authors can determine whether or not submission will jeopardize ACM publication. Authors may submit to ACM conferences and journals revised versions of papers that appeared previously in refereed or formally reviewed publications or under consideration for such publication elsewhere if: the paper has been substantially revised (this generally means that at least 25% of the paper is material not previously published; however, this is a somewhat subjective requirement that is left up to each publication to interpret); upon submission, the author notifies the Editor-in-Chief(s) or Program Chair(s) that the paper has been previously published or simultaneously submitted; and the published policies of the publications or conferences involved do not prohibit this. The ACM Publications Board discourages the following activities, even when the papers are substantially revised: submission of papers previously published in refereed journals to ACM conferences and journals; and submission of papers previously published in formally reviewed conference proceedings to ACM conferences. Editors-in-Chief and Program Chairs have substantial discretion in determining if special circumstances warrant republication or simultaneous submission of a paper. In some cases, conferences may specifically authorize simultaneous submission of identical papers to related conferences with overlapping submission periods. In addition, some journals may invite papers from certain conferences for special journal issues. This may lead to acceptance without substantial revision. Editors and Program Chairs may authorize republication of papers without substantial revision under other special circumstances as well, for example, republication of a historically significant paper as part of a retrospective. In any case where a paper is republished without substantial revision, any prior publication should be noted on the title page of the paper. Explicit permission must be obtained from the copyright holder before papers not copyrighted by ACM may be republished.