COMMUNICATIONS OF THE ACM
Trusted insights for computing’s leading professionals.
Communications of the ACM is the leading monthly print and online magazine for the computing and information technology fields.
Communications is recognized as the most trusted and knowledgeable source of industry information for today’s computing professional.
Communications brings its readership in-depth coverage of emerging areas of computer science, new trends in information technology,
and practical applications. Industry leaders use Communications as a platform to present and debate various technology implications,
public policies, engineering challenges, and market trends. The prestige and unmatched reputation that Communications of the ACM
enjoys today is built upon a 50-year commitment to high-quality editorial content and a steadfast dedication to advancing the arts,
sciences, and applications of information technology.
P
LEASE RECYCL
E
T
HIS M A GAZIN
E
ACM, the world’s largest educational
and scientific computing society, delivers
resources that advance computing as a
science and profession. ACM provides the
computing field’s premier Digital Library
and serves its members and the computing
profession with leading-edge publications,
conferences, and career resources.
Executive Director and CEO
Vicki L. Hanson
Deputy Executive Director and COO
Patricia Ryan
Director, Office of Information Systems
Wayne Graves
Director, Office of Financial Services
Darren Ramdin
Director, Office of SIG Services
Donna Cappo
Director, Office of Publications
Scott E. Delman
ACM COUNCIL
President
Cherri M. Pancake
Vice-President
Elizabeth Churchill
Secretary/Treasurer
Yannis Ioannidis
Past President
Alexander L. Wolf
Chair, SGB Board
Jeff Jortner
Co-Chairs, Publications Board
Jack Davidson and Joseph Konstan
Members-at-Large
Gabriele Anderst-Kotis; Susan Dumais;
Claudia Bauzer Mederios; Elizabeth D. Mynatt;
Pamela Samuelson; Theo Schlossnagle;
Eugene H. Spafford
SGB Council Representatives
Sarita Adve; Jeanna Neefe Matthews
BOARD CHAIRS
Education Board
Mehran Sahami and Jane Chu Prey
Practitioners Board
Terry Coatta and Stephen Ibaraki
REGIONAL COUNCIL CHAIRS
ACM Europe Council
Chris Hankin
ACM India Council
Abhiram Ranade
ACM China Council
Wenguang Chen
PUBLICATIONS BOARD
Co-Chairs
Jack Davidson; Joseph Konstan
Board Members
Phoebe Ayers; Ed ward A. Fox;
Chris Hankin; Xiang-Yang Li;
Sue Moon; Michael L. Nelson;
Sharon Oviatt; Eugene H. Spafford;
Stephen N. Spencer; Robert Walker;
Julie R. Williamson
ACM U.S. Public Policy Office
Adam Eisgrau,
Director of Global Policy and Public Affairs
1701 Pennsylvania Ave N W, Suite 300,
Washington, DC 20006 USA
T (202) 659-9711; F (202) 667-1066
Computer Science Teachers Association
Jake Baskin
Executive Director
STAFF
DIRECTOR OF PUBLICATIONS
Scott E. Delman
cacm-publisher@cacm.acm.org
Executive Editor
Diane Crawford
Managing Editor
Thomas E. Lambert
Senior Editor
Andrew Rosenbloom
Senior Editor/News
Lawrence M. Fisher
Web Editor
David Roman
Rights and Permissions
Deborah Cotton
Editorial Assistant
Jade Morris
Art Director
Andrij Borys
Associate Art Director
Margaret Gray
Assistant Art Director
Mia Angelica Balaquiot
Production Manager
Bernadette Shade
Advertising Sales Account Manager
Ilia Rodriguez
Columnists
David Anderson; Michael Cusumano;
Peter J. Denning; Mark Guzdial;
Thomas Haigh; Leah Hoffmann; Mari Sako;
Pamela Samuelson; Marshall Van Alstyne
CONTACT POINTS
Copyright permission
permissions@hq.acm.org
Calendar items
calendar@cacm.acm.org
Change of address
acmhelp@acm.org
Letters to the Editor
letters@cacm.acm.org
WEBSITE
http://cacm.acm.org
WEB BOARD
Chair
James Landay
Board Members
Marti Hearst; Jason I. Hong;
Jeff Johnson; Wendy E. MacKay
AUTHOR GUIDELINES
http://cacm.acm.org/about-
communications/author-center
ACM ADVERTISING DEPARTMENT
2 Penn Plaza, Suite 701, New York, N Y
10121-0701
T (212) 626-0686
F (212) 869-0481
Advertising Sales Account Manager
Ilia Rodriguez
ilia.rodriguez@hq.acm.org
Media Kit acmmediasales@acm.org
Association for Computing Machinery
(ACM)
2 Penn Plaza, Suite 701
New York, N Y 10121-0701 USA
T (212) 869-7440; F (212) 869-0481
EDITORIAL BOARD
EDITOR-IN-CHIEF
Andrew A. Chien
eic@cacm.acm.org
Deputy to the Editor-in-Chief
Lihan Chen
cacm.deputy.to. eic@gmail.com
SENIOR EDITOR
Moshe Y. Vardi
NEWS
Co-Chairs
William Pulleyblank and Marc Snir
Board Members
Monica Divitini; Mei Kobayashi;
Michael Mitzenmacher; Rajeev Rastogi;
François Sillion
VIEWPOIN TS
Co-Chairs
Tim Finin; Susanne E. Hambrusch;
John Leslie King; Paul Rosenbloom
Board Members
Stefan Bechtold; Michael L. Best; Judith Bishop;
Andrew W. Cross; Mark Guzdial; Haym B. Hirsch;
Richard Ladner; Carl Landwehr; Beng Chin Ooi;
Francesca Rossi; Loren Terveen;
Marshall Van Alstyne; Jeannette Wing;
Susan J. Winter
PRAC TICE
Co-Chairs
Stephen Bourne and Theo Schlossnagle
Board Members
Eric Allman; Samy Bahra; Peter Bailis;
Terry Coatta; Stuart Feldman; Nicole Forsgren;
Camille Fournier; Jessie Frazelle;
Benjamin Fried; Tom Killalea; Tom Limoncelli;
Kate Matsudaira; Marshall Kirk McKusick;
Erik Meijer; George Neville-Neil;
Jim Waldo; Meredith Whittaker
CONTRIBUTED ARTICLES
Co-Chairs
James Larus and Gail Murphy
Board Members
William Aiello; Robert Austin; Kim Bruce;
Alan Bundy; Peter Buneman; Carl Gut win;
Yannis Ioannidis; Gal A. Kaminka;
Ashish Kapoor; Kristin Lauter; Igor Markov;
Bernhard Nebel; Lionel M. Ni; Adrian Perrig;
Marie-Christine Rousset; Krishan Sabnani;
m.c. schraefel; Ron Shamir; Alex Smola;
Josep Torrellas; Sebastian Uchitel;
Hannes Werthner; Reinhard Wilhelm
RESEARCH HIGHLIGHTS
Co-Chairs
Azer Bestavros and Shriram Krishnamurthi
Board Members
Martin Abadi; Amr El Abbadi; Sanjeev Arora;
Michael Backes; Maria-Florina Balcan;
David Brooks; Stuart K. Card; Jon Crowcroft;
Alexei Efros; Bryan Ford; Alon Halevy;
Gernot Heiser; Takeo Igarashi; Sven Koenig;
Greg Morrisett; Tim Roughgarden;
Guy Steele, Jr.; Robert Williamson;
Margaret H. Wright; Nicholai Zeldovich;
Andreas Zeller
SPECIAL SECTIONS
Co-Chair
Sriram Rajamani
Board Members
Tao Xie; Kenjiro Taura; David Padua
ACM Copyright Notice
Copyright © 2018 by Association for
Computing Machinery, Inc. (ACM).
Permission to make digital or hard copies
of part or all of this work for personal
or classroom use is granted without
fee provided that copies are not made
or distributed for profit or commercial
advantage and that copies bear this
notice and full citation on the first
page. Copyright for components of this
work owned by others than ACM must
be honored. Abstracting with credit is
permitted. To copy other wise, to republish,
to post on servers, or to redistribute to
lists, requires prior specific permission
and/or fee. Request permission to publish
from permissions@hq.acm.org or fax
(212) 869-0481.
For other copying of articles that carry a
code at the bottom of the first or last page
or screen display, copying is permitted
provided that the per-copy fee indicated
in the code is paid through the Copyright
Clearance Center; www.copyright.com.
Subscriptions
An annual subscription cost is included
in ACM member dues of $99 ($40 of
which is allocated to a subscription to
Communications); for students, cost
is included in $42 dues ($20 of which
is allocated to a Communications
subscription). A nonmember annual
subscription is $269.
ACM Media Advertising Policy
Communications of the ACM and other
ACM Media publications accept advertising
in both print and electronic formats. All
advertising in ACM Media publications is
at the discretion of ACM and is intended
to provide financial support for the various
activities and services for ACM members.
Current advertising rates can be found
by visiting http://www.acm-media.org or
by contacting ACM Media Sales at
(212) 626-0686.
Single Copies
Single copies of Communications of the
ACM are available for purchase. Please
contact acmhelp@acm.org.
COMMUNICATIONS OF THE ACM
(ISSN 0001-0782) is published monthly
by ACM Media, 2 Penn Plaza, Suite 701,
New York, N Y 10121-0701. Periodicals
postage paid at New York, NY 10001,
and other mailing offices.
POSTMASTER
Please send address changes to
Communications of the ACM
2 Penn Plaza, Suite 701
New York, N Y 10121-0701 USA
Printed in the USA.