Proceedings of the 20th international conference companion on World wide web

It is our great pleasure to welcome you to the World Wide Web Conference (WWW) held during March 28--April 1, 2011, at the Hyderabad International Convention Centre in Hyderabad, India. The WWW Conference is the premier annual forum for sharing, discussing, and debating the latest research developments on Web technologies as well as on applications. Many novel research results are presented every year at WWW and we are particularly pleased with presenting you this year with an exciting technical program. The main component of the program is represented by the research papers. We organized the submission of research papers into 12 tracks. These tracks cover all aspects of the Web from computing infrastructure and data analysis techniques to social systems and networks. The track chairs worked with us to refine each track into a number of topics. By just looking at these tracks and topics you can appreciate how many different research questions and directions exist in the area of the Web. In response to the call for papers, we received 658 research submissions. Right after the submission deadline, with help from the track chairs, we checked every submission to make sure that it was submitted to the most appropriate track. Each submission was carefully reviewed by at least three reviewers and by the first week of January 2011, the track chairs formed a rank ordering of the submissions in their respective tracks. A PC meeting was then held on January 10--11, 2011 at Yahoo! in Santa Clara (California), during which candidates for acceptance were discussed and submissions with conflicting reviews were carefully analyzed by the track chairs. All the PC meeting participants greatly contributed to the discussions and helped us in making particularly difficult decisions. The result is a research paper program consisting of 81 papers that you find in the WWW 2011 Paper Proceedings. The research paper program is complemented by the following supplemental tracks. The special research track, titled "Web for the Emerging Regions," focuses on research contributions in the problem space of extending the Web to emerging regions. The poster track received 202 submissions of which 61 were accepted; in addition, 29 papers from the research paper track were recommended for poster publication, thus resulting in a total of 90 poster papers. Continuing the tradition from last year, we have a demo track; the goal of this track is to make possible for researchers to present live demos of their systems and applications. A total of 52 demos were submitted from which 25 were selected for presentation at the conference. The technical program also includes tutorials, workshops, panels, W3C track, Industrial track, and PhD Symposium. Material corresponding to these tracks can be found in the WWW 2011 Supplemental Proceedings.