A System for Web Widget Discovery Using Semantic Distance between User Intent and Social Tags -- An Automated Multiscale Map of Conversations: Mothers and Matters -- How Influential Are You: Detecting Influential Bloggers in a Blogging Community -- A Simulation Model Using Transaction Cost Economics to Analyze the Impact of Social Media on Online Shopping -- Predicting Group Evolution in the Social Network -- Interpolating between Random Walks and Shortest Paths: A Path Functional Approach -- Dynamic Targeting in an Online Social Medium -- Connecting with Active People Matters: The Influence of an Online Community on Physical Activity Behavior -- Detecting Overlapping Communities in Location-Based Social Networks -- CrowdLang: A Programming Language for the Systematic Exploration of Human Computation Systems -- Experiments in Cross-Lingual Sentiment Analysis in Discussion Forums -- Quality Assessment of User Comments on Mobile Platforms Considering Channel of Activation and Platform Design -- A Method Based on Congestion Game Theory for Determining Electoral Tendencies -- A Model to Represent Human Social Relationships in Social Network Graphs -- C4PS - Helping Facebookers Manage Their Privacy Settings -- Dynamic "Participative Rules" in Serious Games, New Ways for Evaluation? -- Mobile Phones, Family and Personal Relationships: The Case of Indonesian Micro-entrepreneurs -- An Analysis of Topical Proximity in the Twitter Social Graph -- A Foresight Support System to Manage Knowledge on Information Society Evolution -- How Many Answers Are Enough? Optimal Number of Answers for Q&A Sites -- Analysis and Support of Lifestyle via Emotions Using Social Media -- A Computational Analysis of Joint Decision Making Processes -- Collaboratively Constructing a VDL-Based Icon System for Knowledge Tagging -- A Multi-dimensional and Event-Based Model for Trust Computation in the Social Web -- On Recommending Hashtags in Twitter Networks -- A Framework for the Design and Synthesis of CoordinatedSocial Systems -- Swayed by Friends or by the Crowd? -- Are Twitter Users Equal in Predicting Elections? A Study of User Groups in Predicting 2012 U.S. Republican Presidential Primaries.-Web Page Recommendation Based on Semantic Web Usage Mining -- Scalable Analysis for Large Social Networks: The Data-Aware Mean-Field Approach -- A Survey of Recommender Systems in Twitter -- Multi-view Content-Based User Recommendation Scheme for Following Users in Twitter -- Spam Fighting in Social Tagging Systems -- The Multidimensional Study of Viral Campaigns as Branching Processes -- Models of Social Groups in Blogosphere Based on Information about Comment Addressees and Sentiments -- Dark Retweets: Investigating Non-conventional Retweeting Patterns.-Studying Paths of Participation in Viral Diffusion Process -- Paradox of Proximity - Trust and Provenance within the Context of Social Networks and Policy -- Namelings: Discover Given Name Relatedness Based on Data from the SocialWeb -- SocialTrends: A Web Application for Monitoring and Visualizing Users in Social Media -- Demonstration of Dynamic Targeting in an Online Social Medium -- Navigating between Chaos and Bureaucracy: Backgrounding Trust in Open-Content Communities.-.

This book constitutes the proceedings of the 4th International Conference on Social Informatics, SocInfo 2012, held in Lausanne, Switzerland, in December 2012. The 21 full papers, 18 short papers  included in this volume were carefully reviewed and selected from 61 submissions. The papers are organized in topical sections named: social choice mechanisms in the e-society,computational models of social phenomena, social simulation, web mining and its social interpretations, algorithms and protocols inspired by human societies, socio-economic systems and applications, trust, privacy, risk and security in social contexts.