A survey of Twitter research: data model, graph structure, sentiment analysis and attacksA survey of Twitter research: data model, graph structure, sentiment analysis and attacks Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2023-02-022021enThis work has been supported by the European project CONCORDIA, with grant number 830927 (EUROPEAN COMMISSION Directorate - General Communications Networks, Content and Technology).Twitter is the third most popular worldwide Online Social Network (OSN) after Facebook and Instagram. Compared to other OSNs, it has a simple data model and a straightforward data access API. This makes it ideal for social network studies attempting to analyze the patterns of online behavior, the structure of the social graph, the sentiment towards various entities and the nature of malicious attacks in a vivid network with hundreds of millions of users. Indeed, Twitter has been established as a major research platform, utilized in more than ten thousands research articles over the last ten years. Although there are excellent review and comparison studies for most of the research that utilizes Twitter, there are limited efforts to map this research terrain as a whole. Here we present an effort to map the current research topics in Twitter focusing on three major areas: the structure and properties of the social graph, sentiment analysis and threats such as spam, bots, fake news and hate speech. We also present Twitter’s basic data model and best practices for sampling and data access. This survey also lays the ground of computational techniques used in these areas such as Graph Sampling, Natural Language Processing and Machine Learning. Along with existing reviews and comparison studies, we also discuss the key findings and the state of the art in these methods. Overall, we hope that this survey will help researchers create a clear conceptual model of Twitter and act as a guide to expand further the topics presented.http://creativecommons.org/licenses/by/4.0/Expert Systems with Applications164 Antonakaki Despoina Fragopoulou, Paraskevi Ioannidis Sotirios Ιωαννιδης Σωτηριος Elsevier Social networks Twitter Survey Social graph Sentiment analysis Spam Bots Fake news Hate speech