Over the past 15 years, the volume, richness and quality of data collected from the combined social networking platforms has increased beyond all expectation, providing researchers from a variety of disciplines to use it in their research. Perhaps more impactfully, it has provided the foundation for a range of new products and services, transforming industries such as advertising and marketing, as well as bringing the challenges of sharing personal data into the public consciousness. But how to make sense of the ever-increasing volume of big social data so that we can better understand and improve the user experience in increasingly complex, data-driven digital systems. This link with usability and the user experience of data-driven system bridges into the wider field of human-computer interaction (HCI), attracting interdisciplinary researchers as we see the demand for consumer technologies, software and systems, as well as the integration of social networks into our everyday lives. The fact that the data largely posted on social networks tends to be textual, provides a further link to linguistics, psychology and psycholinguistics to better understand the relationship between human behaviours offline and online. I would like to dedicate this thesis to my father, who always believed in me and pushed me forward towards my goals, his guidance and encouragement were always invaluable, I am forever grateful to him (may his soul rest in peace). My sincere thanks to my mother, her prayer to me is what sustained me thus far. My brothers (Hossam and Ahmed) and sisters (Hala and Heba) and all my family members for their continuing support during my PhD journey.Last but not least, words cannot express how grateful I am to my beloved wife Marwa and my two darling daughters, I cannot thank her enough for her sacrifices, companionship, love, support and encouragement you have provided in every minute of this journey. I am beyond grateful to you -without your precious support it would not be possible to finally complete this chapter of my life.