Higher Education Press and Springer-Verlag Berlin Heidelberg Posted on May 27, 2014 by SCG DR Copyright Holders: Higher Education Press and Springer-Verlag Berlin Heidelberg Self-archiving policy Conditions Accepted version: √ permission from publisher is required Published version: √ permission from publisher is required Remarks: No part of a paper which has been published by Frontiers of Computer Science may be reproduced or published elsewhere without the written permission of the publisher. Verification Date: 26.05.2014 02.06.2014