I. INTRODUCTION
Personal social networks are big and cluttered, yet contain highly valuable information [1]. Taking Facebook along, as of 2014, its market value already exceeds 156 billion US dollar. Organizing users’ friends into circles or communities is a fundamental task in social network research [2] [3]. Social network sites like Facebook and Twitter allow users to manually categorize their friends into social circles, but this process is laborious, error-prone and inadaptable to changes.