1. Department of Information Science, College of Humanities and Social Sciences, King Saud University, Riyadh P.O. Box 11451, Saudi Arabia
2. School of Informatics, The University of Edinburgh, 10 Crichton St., Edinburgh EH8 9AB, UK
3. Department of Computer Science, College of Computer and Information Sciences, King Saud University, Riyadh P.O. Box 11451, Saudi Arabia
4. Computer Science Department, Community College, King Saud University, Riyadh P.O. Box 11451, Saudi Arabia